diff --git a/tests/qemu-iotests/017 b/tests/qemu-iotests/017
index 0a4b854..585512b 100755
--- a/tests/qemu-iotests/017
+++ b/tests/qemu-iotests/017
@@ -66,7 +66,7 @@
 echo
 
 TEST_IMG=$TEST_IMG_SAVE
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo "Filling test image"
 echo
diff --git a/tests/qemu-iotests/017.out b/tests/qemu-iotests/017.out
index 8fc9241..f439d3e 100644
--- a/tests/qemu-iotests/017.out
+++ b/tests/qemu-iotests/017.out
@@ -269,7 +269,7 @@
 No errors were found on the image.
 Creating test image with backing file
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Filling test image
 
 === IO: pattern 1
diff --git a/tests/qemu-iotests/018 b/tests/qemu-iotests/018
index c69ce09..191b461 100755
--- a/tests/qemu-iotests/018
+++ b/tests/qemu-iotests/018
@@ -66,7 +66,7 @@
 echo
 
 TEST_IMG="$TEST_IMG_SAVE.orig"
-_make_test_img -b "$TEST_IMG_SAVE.base" 6G
+_make_test_img -b "$TEST_IMG_SAVE.base" -F $IMGFMT 6G
 
 echo "Filling test image"
 echo
diff --git a/tests/qemu-iotests/018.out b/tests/qemu-iotests/018.out
index 5df9667..0ab664c 100644
--- a/tests/qemu-iotests/018.out
+++ b/tests/qemu-iotests/018.out
@@ -269,7 +269,7 @@
 No errors were found on the image.
 Creating test image with backing file
 
-Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Filling test image
 
 === IO: pattern 1
diff --git a/tests/qemu-iotests/019 b/tests/qemu-iotests/019
index 813a84a..d3c1125 100755
--- a/tests/qemu-iotests/019
+++ b/tests/qemu-iotests/019
@@ -74,7 +74,7 @@
 echo
 
 TEST_IMG="$TEST_IMG_SAVE.orig"
-_make_test_img -b "$TEST_IMG_SAVE.base" 6G
+_make_test_img -b "$TEST_IMG_SAVE.base" -F $IMGFMT 6G
 
 echo "Filling test image"
 echo
@@ -98,7 +98,8 @@
     echo
     echo Testing conversion with $backing_option"$TEST_IMG.base" | _filter_testdir | _filter_imgfmt
     echo
-    $QEMU_IMG convert -f $IMGFMT -O $IMGFMT $backing_option"$TEST_IMG.base" "$TEST_IMG.orig" "$TEST_IMG"
+    $QEMU_IMG convert -f $IMGFMT -O $IMGFMT $backing_option"$TEST_IMG.base" \
+        -o backing_fmt=$IMGFMT "$TEST_IMG.orig" "$TEST_IMG"
 
     echo "Checking if backing clusters are allocated when they shouldn't"
     echo
diff --git a/tests/qemu-iotests/019.out b/tests/qemu-iotests/019.out
index 17a7c03..0fa73bd 100644
--- a/tests/qemu-iotests/019.out
+++ b/tests/qemu-iotests/019.out
@@ -269,7 +269,7 @@
 No errors were found on the image.
 Creating test image with backing file
 
-Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT.orig', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Filling test image
 
 === IO: pattern 43
diff --git a/tests/qemu-iotests/020 b/tests/qemu-iotests/020
index b488000..a078293 100755
--- a/tests/qemu-iotests/020
+++ b/tests/qemu-iotests/020
@@ -70,7 +70,7 @@
 echo
 
 TEST_IMG="$TEST_IMG_SAVE"
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo "Filling test image"
 echo
@@ -131,7 +131,7 @@
 # Filter out newlines and collapse spaces
 backing=$(echo "$backing" | tr -d '\n' | tr -s ' ')
 
-_make_test_img -b "$backing"
+_make_test_img -b "$backing" -F $IMGFMT
 
 # Just write anything so committing will not be a no-op
 $QEMU_IO -c 'writev 0 64k' "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/020.out b/tests/qemu-iotests/020.out
index 4668ac5..5936bc1 100644
--- a/tests/qemu-iotests/020.out
+++ b/tests/qemu-iotests/020.out
@@ -269,7 +269,7 @@
 No errors were found on the image.
 Creating test image with backing file
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Filling test image
 
 === IO: pattern 1
@@ -1079,7 +1079,7 @@
 Testing failing commit
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=json:{'driver': 'IMGFMT',, 'file': { 'driver': 'blkdebug',, 'inject-error': [{ 'event': 'write_aio',, 'errno': 28,, 'once': true }],, 'image': { 'driver': 'file',, 'filename': 'TEST_DIR/t.IMGFMT.base' }}}
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=json:{'driver': 'IMGFMT',, 'file': { 'driver': 'blkdebug',, 'inject-error': [{ 'event': 'write_aio',, 'errno': 28,, 'once': true }],, 'image': { 'driver': 'file',, 'filename': 'TEST_DIR/t.IMGFMT.base' }}} backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Block job failed: No space left on device
diff --git a/tests/qemu-iotests/024 b/tests/qemu-iotests/024
index e2e7662..12aceb2 100755
--- a/tests/qemu-iotests/024
+++ b/tests/qemu-iotests/024
@@ -83,7 +83,7 @@
 echo "Creating COW image"
 echo
 
-_make_test_img -b "$TEST_IMG.base_old" 1G
+_make_test_img -b "$TEST_IMG.base_old" -F $IMGFMT 1G
 io_pattern writev 0 $((4 * CLUSTER_SIZE)) 0 1 0x33
 io_pattern writev $((8 * CLUSTER_SIZE)) $((4 * CLUSTER_SIZE)) 0 1 0x33
 
@@ -109,7 +109,7 @@
 echo
 echo Rebase and test again
 echo
-$QEMU_IMG rebase -b "$TEST_IMG.base_new" "$TEST_IMG"
+$QEMU_IMG rebase -b "$TEST_IMG.base_new" -F $IMGFMT "$TEST_IMG"
 io_pattern readv $((0 * CLUSTER_SIZE)) $CLUSTER_SIZE 0 1 0x33
 io_pattern readv $((1 * CLUSTER_SIZE)) $CLUSTER_SIZE 0 1 0x33
 io_pattern readv $((2 * CLUSTER_SIZE)) $CLUSTER_SIZE 0 1 0x33
@@ -159,7 +159,7 @@
 
 TEST_IMG=$BASE_OLD _make_test_img 1M
 TEST_IMG=$BASE_NEW _make_test_img 1M
-TEST_IMG=$OVERLAY _make_test_img -b "$BASE_OLD_OREL" 1M
+TEST_IMG=$OVERLAY _make_test_img -b "$BASE_OLD_OREL" -F $IMGFMT 1M
 
 echo
 
@@ -176,11 +176,11 @@
 echo
 
 pushd "$TEST_DIR" >/dev/null
-$QEMU_IMG rebase -f "$IMGFMT" -b "$BASE_NEW_OREL" "$OVERLAY_WREL"
+$QEMU_IMG rebase -f "$IMGFMT" -b "$BASE_NEW_OREL" -F $IMGFMT "$OVERLAY_WREL"
 popd >/dev/null
 
 # Verify the backing path is correct
-TEST_IMG=$OVERLAY _img_info | grep '^backing file'
+TEST_IMG=$OVERLAY _img_info | grep '^backing file:'
 
 echo
 
diff --git a/tests/qemu-iotests/024.out b/tests/qemu-iotests/024.out
index 024dc78..973a5a3 100644
--- a/tests/qemu-iotests/024.out
+++ b/tests/qemu-iotests/024.out
@@ -33,7 +33,7 @@
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Creating COW image
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base_old
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base_old backing_fmt=IMGFMT
 === IO: pattern 0x33
 wrote 262144/262144 bytes at offset 0
 256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -146,7 +146,7 @@
 
 Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=1048576
 Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=t.IMGFMT.base_old
+Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=t.IMGFMT.base_old backing_fmt=IMGFMT
 
 wrote 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
diff --git a/tests/qemu-iotests/028 b/tests/qemu-iotests/028
index 797dae5..5d043ce 100755
--- a/tests/qemu-iotests/028
+++ b/tests/qemu-iotests/028
@@ -76,7 +76,7 @@
 echo
 
 TEST_IMG="$TEST_IMG_SAVE"
-_make_test_img -b "$TEST_IMG.base" $image_size
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $image_size
 
 echo "Filling test image"
 echo
@@ -101,7 +101,7 @@
 _check_test_img
 
 # Rebase it on top of its base image
-$QEMU_IMG rebase -b "$TEST_IMG.base" "$TEST_IMG"
+$QEMU_IMG rebase -b "$TEST_IMG.base" -F $IMGFMT "$TEST_IMG"
 
 echo
 echo block-backup
diff --git a/tests/qemu-iotests/028.out b/tests/qemu-iotests/028.out
index 37aed84..12f82c6 100644
--- a/tests/qemu-iotests/028.out
+++ b/tests/qemu-iotests/028.out
@@ -70,7 +70,7 @@
 No errors were found on the image.
 Creating test image with backing file
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294968832 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294968832 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Filling test image
 
 === IO: pattern 196
diff --git a/tests/qemu-iotests/030 b/tests/qemu-iotests/030
index 1cdd7e2..256b2bf 100755
--- a/tests/qemu-iotests/030
+++ b/tests/qemu-iotests/030
@@ -32,8 +32,12 @@
 
     def setUp(self):
         iotests.create_image(backing_img, TestSingleDrive.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, mid_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % mid_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img,
+                 '-F', 'raw', mid_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % mid_img,
+                 '-F', iotests.imgfmt, test_img)
         qemu_io('-f', 'raw', '-c', 'write -P 0x1 0 512', backing_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x1 524288 512', mid_img)
         self.vm = iotests.VM().add_drive("blkdebug::" + test_img,
@@ -199,7 +203,8 @@
         iotests.create_image(self.imgs[0], self.image_len)
         for i in range(1, self.num_imgs):
             qemu_img('create', '-f', iotests.imgfmt,
-                     '-o', 'backing_file=%s' % self.imgs[i-1], self.imgs[i])
+                     '-o', 'backing_file=%s' % self.imgs[i-1],
+                     '-F', 'raw' if i == 1 else iotests.imgfmt, self.imgs[i])
 
         # Put data into the images we are copying data from
         odd_img_indexes = [x for x in reversed(range(self.num_imgs)) if x % 2 == 1]
@@ -544,7 +549,8 @@
             qemu_io('-f', iotests.imgfmt,
                     '-c', 'write -P 0x55 0 1024', backing_img)
             qemu_img('create', '-f', iotests.imgfmt,
-                     '-o', 'backing_file=%s' % backing_img, child_img)
+                     '-o', 'backing_file=%s' % backing_img,
+                     '-F', iotests.imgfmt, child_img)
             opts.append("children.%d.file.filename=%s" % (i, child_img))
             opts.append("children.%d.node-name=node%d" % (i, i))
 
@@ -585,7 +591,9 @@
 
     def setUp(self):
         iotests.create_image(backing_img, self.backing_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img, str(self.image_len))
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img,
+                 '-F', 'raw', test_img, str(self.image_len))
         self.vm = iotests.VM().add_drive(test_img)
         self.vm.launch()
 
@@ -848,7 +856,9 @@
     def setUp(self):
         qemu_img('create', backing_img, str(TestStreamStop.image_len))
         qemu_io('-f', 'raw', '-c', 'write -P 0x1 0 32M', backing_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img,
+                 '-F', 'raw', test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x1 32M 32M', test_img)
         self.vm = iotests.VM().add_drive("blkdebug::" + test_img)
         self.vm.launch()
@@ -879,7 +889,9 @@
     def setUp(self):
         qemu_img('create', backing_img, str(TestSetSpeed.image_len))
         qemu_io('-f', 'raw', '-c', 'write -P 0x1 0 32M', backing_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img,
+                 '-F', 'raw', test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x1 32M 32M', test_img)
         self.vm = iotests.VM().add_drive('blkdebug::' + test_img)
         self.vm.launch()
diff --git a/tests/qemu-iotests/034 b/tests/qemu-iotests/034
index da4cea1..ac2d687 100755
--- a/tests/qemu-iotests/034
+++ b/tests/qemu-iotests/034
@@ -58,7 +58,7 @@
 
 TEST_IMG="$TEST_IMG_SAVE"
 
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo
 echo "== zero write with backing file =="
diff --git a/tests/qemu-iotests/034.out b/tests/qemu-iotests/034.out
index 0764ead..478205a 100644
--- a/tests/qemu-iotests/034.out
+++ b/tests/qemu-iotests/034.out
@@ -4,7 +4,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
 wrote 1048576/1048576 bytes at offset 0
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == zero write with backing file ==
 wrote 196608/196608 bytes at offset 65536
diff --git a/tests/qemu-iotests/037 b/tests/qemu-iotests/037
index e6517ac..e1187ac 100755
--- a/tests/qemu-iotests/037
+++ b/tests/qemu-iotests/037
@@ -74,7 +74,7 @@
 
 TEST_IMG="$TEST_IMG_SAVE"
 
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo
 echo "== COW in a single cluster =="
diff --git a/tests/qemu-iotests/037.out b/tests/qemu-iotests/037.out
index cd6710c..30ef989 100644
--- a/tests/qemu-iotests/037.out
+++ b/tests/qemu-iotests/037.out
@@ -514,7 +514,7 @@
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 512/512 bytes at offset 130560
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == COW in a single cluster ==
 wrote 2048/2048 bytes at offset 0
diff --git a/tests/qemu-iotests/038 b/tests/qemu-iotests/038
index 707e2d7..a253231f5 100755
--- a/tests/qemu-iotests/038
+++ b/tests/qemu-iotests/038
@@ -71,7 +71,7 @@
 
 TEST_IMG="$TEST_IMG_SAVE"
 
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo
 echo "== Some concurrent requests touching the same cluster =="
diff --git a/tests/qemu-iotests/038.out b/tests/qemu-iotests/038.out
index 0bdfb19..fe21085 100644
--- a/tests/qemu-iotests/038.out
+++ b/tests/qemu-iotests/038.out
@@ -514,7 +514,7 @@
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 65536/65536 bytes at offset 16711680
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == Some concurrent requests touching the same cluster ==
 wrote 65536/65536 bytes at offset XXX
diff --git a/tests/qemu-iotests/039 b/tests/qemu-iotests/039
index ddce48a..42f6503 100755
--- a/tests/qemu-iotests/039
+++ b/tests/qemu-iotests/039
@@ -133,7 +133,8 @@
 
 TEST_IMG="$TEST_IMG".base _make_test_img -o "compat=1.1,lazy_refcounts=on" $size
 
-_make_test_img -o "compat=1.1,lazy_refcounts=on,backing_file=$TEST_IMG.base" $size
+_make_test_img -o "compat=1.1,lazy_refcounts=on,backing_file=$TEST_IMG.base" \
+    -F $IMGFMT $size
 
 $QEMU_IO -c "write 0 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG commit "$TEST_IMG"
diff --git a/tests/qemu-iotests/039.out b/tests/qemu-iotests/039.out
index bdafa3a..e52484d 100644
--- a/tests/qemu-iotests/039.out
+++ b/tests/qemu-iotests/039.out
@@ -66,7 +66,7 @@
 
 == Committing to a backing file with lazy_refcounts=on ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Image committed.
diff --git a/tests/qemu-iotests/040 b/tests/qemu-iotests/040
index 32c82b4..f58f50d 100755
--- a/tests/qemu-iotests/040
+++ b/tests/qemu-iotests/040
@@ -80,8 +80,11 @@
 
     def setUp(self):
         iotests.create_image(backing_img, self.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, mid_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % mid_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', mid_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % mid_img,
+                 '-F', iotests.imgfmt, test_img)
         qemu_io('-f', 'raw', '-c', 'write -P 0xab 0 524288', backing_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xef 524288 524288', mid_img)
         self.vm = iotests.VM().add_drive(test_img, "node-name=top,backing.node-name=mid,backing.backing.node-name=base", interface="none")
@@ -305,10 +308,16 @@
             if exception.errno != errno.EEXIST:
                 raise
         iotests.create_image(self.backing_img_abs, TestRelativePaths.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.backing_img_abs, self.mid_img_abs)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.mid_img_abs, self.test_img)
-        qemu_img('rebase', '-u', '-b', self.backing_img, self.mid_img_abs)
-        qemu_img('rebase', '-u', '-b', self.mid_img, self.test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % self.backing_img_abs,
+                 '-F', 'raw', self.mid_img_abs)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % self.mid_img_abs,
+                 '-F', iotests.imgfmt, self.test_img)
+        qemu_img('rebase', '-u', '-b', self.backing_img,
+                 '-F', 'raw', self.mid_img_abs)
+        qemu_img('rebase', '-u', '-b', self.mid_img,
+                 '-F', iotests.imgfmt, self.test_img)
         qemu_io('-f', 'raw', '-c', 'write -P 0xab 0 524288', self.backing_img_abs)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xef 524288 524288', self.mid_img_abs)
         self.vm = iotests.VM().add_drive(self.test_img)
@@ -371,8 +380,11 @@
 
     def setUp(self):
         qemu_img('create', backing_img, str(TestSetSpeed.image_len))
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, mid_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % mid_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', mid_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % mid_img,
+                 '-F', iotests.imgfmt, test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x1 0 512', test_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xef 524288 524288', mid_img)
         self.vm = iotests.VM().add_drive('blkdebug::' + test_img)
@@ -410,9 +422,14 @@
 
     def setUp(self):
         iotests.create_image(self.img0, self.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img0, self.img1)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img1, self.img2)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % self.img2, self.img3)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % self.img0, '-F', 'raw', self.img1)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % self.img1,
+                 '-F', iotests.imgfmt, self.img2)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % self.img2,
+                 '-F', iotests.imgfmt, self.img3)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xab 0 128K', self.img1)
         self.vm = iotests.VM().add_drive(self.img3)
         self.vm.launch()
@@ -435,8 +452,12 @@
 
     def setUp(self):
         iotests.create_image(backing_img, self.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, mid_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % mid_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img,
+                 '-F', 'raw', mid_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % mid_img,
+                 '-F', iotests.imgfmt, test_img)
 
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x11 0 512k', mid_img)
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0x22 0 512k', test_img)
diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index b843f88..f0a7bf6 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -44,7 +44,8 @@
 
     def setUp(self):
         iotests.create_image(backing_img, self.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', test_img)
         self.vm = iotests.VM().add_drive(test_img, "node-name=top,backing.node-name=base")
         if iotests.qemu_default_machine == 'pc':
             self.vm.add_drive(None, 'media=cdrom', 'ide')
@@ -157,7 +158,8 @@
         self.assert_no_active_block_jobs()
 
         qemu_img('create', '-f', iotests.imgfmt, '-o', 'cluster_size=%d,backing_file=%s'
-                        % (self.image_len, backing_img), target_img)
+                        % (self.image_len, backing_img),
+                 '-F', 'raw', target_img)
         result = self.vm.qmp(self.qmp_cmd, device='drive0', sync='full',
                              mode='existing', target=self.qmp_target)
         self.assert_qmp(result, 'return', {})
@@ -227,7 +229,8 @@
 
     def setUp(self):
         TestSingleDrive.setUp(self)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, target_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', target_img)
         args = {'driver': iotests.imgfmt,
                 'node-name': self.qmp_target,
                 'file': { 'filename': target_img, 'driver': 'file' } }
@@ -312,7 +315,8 @@
 
     def setUp(self):
         iotests.create_image(backing_img, TestMirrorNoBacking.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', test_img)
         self.vm = iotests.VM().add_drive(test_img)
         self.vm.launch()
 
@@ -329,7 +333,8 @@
     def test_complete(self):
         self.assert_no_active_block_jobs()
 
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, target_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', target_img)
         result = self.vm.qmp('drive-mirror', device='drive0', sync='full',
                              mode='existing', target=target_img)
         self.assert_qmp(result, 'return', {})
@@ -344,7 +349,8 @@
     def test_cancel(self):
         self.assert_no_active_block_jobs()
 
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, target_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', target_img)
         result = self.vm.qmp('drive-mirror', device='drive0', sync='full',
                              mode='existing', target=target_img)
         self.assert_qmp(result, 'return', {})
@@ -363,7 +369,8 @@
         qemu_img('create', '-f', iotests.imgfmt, '-o', 'size=%d'
                         %(TestMirrorNoBacking.image_len), target_backing_img)
         qemu_img('create', '-f', iotests.imgfmt, '-o', 'cluster_size=%d,backing_file=%s'
-                        % (TestMirrorNoBacking.image_len, target_backing_img), target_img)
+                        % (TestMirrorNoBacking.image_len, target_backing_img),
+                 '-F', iotests.imgfmt, target_img)
 
         result = self.vm.qmp('drive-mirror', device='drive0', sync='full',
                              mode='existing', target=target_img)
@@ -382,7 +389,8 @@
 
     def setUp(self):
         iotests.create_image(backing_img, TestMirrorResized.backing_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', test_img)
         qemu_img('resize', test_img, '2M')
         self.vm = iotests.VM().add_drive(test_img)
         self.vm.launch()
@@ -528,7 +536,9 @@
         # Test COW into the target image.  The first half of the
         # cluster at MIRROR_GRANULARITY has to be copied from
         # backing_img, even though sync='top'.
-        qemu_img('create', '-f', iotests.imgfmt, '-ocluster_size=131072,backing_file=%s' %(backing_img), target_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-ocluster_size=131072,backing_file=%s' %(backing_img),
+                 '-F', 'raw', target_img)
         result = self.vm.qmp('drive-mirror', device='drive0', sync='top',
                              on_source_error='ignore',
                              mode='existing', target=target_img)
@@ -548,7 +558,8 @@
         self.vm.shutdown()
 
         # Detach blkdebug to compare images successfully
-        qemu_img('rebase', '-f', iotests.imgfmt, '-u', '-b', backing_img, test_img)
+        qemu_img('rebase', '-f', iotests.imgfmt, '-u', '-b', backing_img,
+                 '-F', 'raw', test_img)
         self.assertTrue(iotests.compare_images(test_img, target_img),
                         'target image does not match source after mirroring')
 
@@ -620,7 +631,8 @@
         self.blkdebug_file = target_img + ".blkdebug"
         iotests.create_image(backing_img, TestWriteErrors.image_len)
         self.create_blkdebug_file(self.blkdebug_file, "write_aio", 5)
-        qemu_img('create', '-f', iotests.imgfmt, '-obacking_file=%s' %(backing_img), test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-obacking_file=%s' %(backing_img), '-F', 'raw', test_img)
         self.vm = iotests.VM().add_drive(test_img)
         self.target_img = 'blkdebug:%s:%s' % (self.blkdebug_file, target_img)
         qemu_img('create', '-f', iotests.imgfmt, '-osize=%d' %(TestWriteErrors.image_len), target_img)
@@ -715,7 +727,8 @@
 
     def setUp(self):
         qemu_img('create', backing_img, str(TestSetSpeed.image_len))
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', test_img)
         self.vm = iotests.VM().add_drive(test_img)
         self.vm.launch()
 
diff --git a/tests/qemu-iotests/042 b/tests/qemu-iotests/042
index 0e85b35..e8f23a1 100755
--- a/tests/qemu-iotests/042
+++ b/tests/qemu-iotests/042
@@ -64,8 +64,8 @@
 echo
 echo "== Rebasing the image =="
 
-$QEMU_IMG rebase -u -b "$TEST_IMG.orig" "$TEST_IMG"
-$QEMU_IMG rebase -b "$TEST_IMG.orig" "$TEST_IMG"
+$QEMU_IMG rebase -u -b "$TEST_IMG.orig" -F $IMGFMT "$TEST_IMG"
+$QEMU_IMG rebase -b "$TEST_IMG.orig" -F $IMGFMT "$TEST_IMG"
 _check_test_img
 
 # success, all done
diff --git a/tests/qemu-iotests/043 b/tests/qemu-iotests/043
index b102e49..3271737 100755
--- a/tests/qemu-iotests/043
+++ b/tests/qemu-iotests/043
@@ -46,7 +46,7 @@
 
 size=128M
 _make_test_img $size
-$QEMU_IMG rebase -u -b "$TEST_IMG" "$TEST_IMG"
+$QEMU_IMG rebase -u -b "$TEST_IMG" -F $IMGFMT "$TEST_IMG"
 
 echo
 echo "== backing file references self =="
@@ -54,8 +54,8 @@
 
 _make_test_img $size
 mv "$TEST_IMG" "$TEST_IMG.base"
-_make_test_img -b "$TEST_IMG.base" $size
-$QEMU_IMG rebase -u -b "$TEST_IMG" "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $size
+$QEMU_IMG rebase -u -b "$TEST_IMG" -F $IMGFMT "$TEST_IMG.base"
 
 echo
 echo "== parent references self =="
@@ -63,12 +63,12 @@
 
 _make_test_img $size
 mv "$TEST_IMG" "$TEST_IMG.1.base"
-_make_test_img -b "$TEST_IMG.1.base" $size
+_make_test_img -b "$TEST_IMG.1.base" -F $IMGFMT $size
 mv "$TEST_IMG" "$TEST_IMG.2.base"
-_make_test_img -b "$TEST_IMG.2.base" $size
+_make_test_img -b "$TEST_IMG.2.base" -F $IMGFMT $size
 mv "$TEST_IMG" "$TEST_IMG.3.base"
-_make_test_img -b "$TEST_IMG.3.base" $size
-$QEMU_IMG rebase -u -b "$TEST_IMG.2.base" "$TEST_IMG.1.base"
+_make_test_img -b "$TEST_IMG.3.base" -F $IMGFMT $size
+$QEMU_IMG rebase -u -b "$TEST_IMG.2.base" -F $IMGFMT "$TEST_IMG.1.base"
 
 echo
 echo "== ancestor references another ancestor =="
@@ -76,17 +76,18 @@
 
 _make_test_img $size
 mv "$TEST_IMG" "$TEST_IMG.1.base"
-_make_test_img -b "$TEST_IMG.1.base" $size
+_make_test_img -b "$TEST_IMG.1.base" -F $IMGFMT $size
 mv "$TEST_IMG" "$TEST_IMG.2.base"
-_make_test_img -b "$TEST_IMG.2.base" $size
+_make_test_img -b "$TEST_IMG.2.base" -F $IMGFMT $size
 
 echo
 echo "== finite chain of length 3 (human) =="
-_img_info --backing-chain
+# Exclude backing format, since qed differs from qcow2 on what gets stored
+_img_info --backing-chain | grep -v '^backing file format:'
 
 echo
 echo "== finite chain of length 3 (json) =="
-_img_info --backing-chain --output=json
+_img_info --backing-chain --output=json | grep -v 'backing-filename-format'
 
 # success, all done
 echo "*** done"
diff --git a/tests/qemu-iotests/043.out b/tests/qemu-iotests/043.out
index 0280f99..63ecb21 100644
--- a/tests/qemu-iotests/043.out
+++ b/tests/qemu-iotests/043.out
@@ -4,20 +4,20 @@
 == backing file references self ==
 qemu-img: Backing file 'TEST_DIR/t.IMGFMT' creates an infinite loop.
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == parent references self ==
 qemu-img: Backing file 'TEST_DIR/t.IMGFMT' creates an infinite loop.
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.1.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.2.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.3.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.1.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.2.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.3.base backing_fmt=IMGFMT
 
 == ancestor references another ancestor ==
 qemu-img: Backing file 'TEST_DIR/t.IMGFMT.2.base' creates an infinite loop.
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.1.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.2.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.1.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.2.base backing_fmt=IMGFMT
 
 == finite chain of length 3 (human) ==
 image: TEST_DIR/t.IMGFMT
diff --git a/tests/qemu-iotests/046 b/tests/qemu-iotests/046
index ecbe5fc..88b3363 100755
--- a/tests/qemu-iotests/046
+++ b/tests/qemu-iotests/046
@@ -69,7 +69,7 @@
 
 mv "$TEST_IMG" "$TEST_IMG.base"
 
-_make_test_img -b "$TEST_IMG.base" 6G
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 6G
 
 echo
 echo "== Some concurrent requests touching the same cluster =="
diff --git a/tests/qemu-iotests/046.out b/tests/qemu-iotests/046.out
index 7078304..b022bcd 100644
--- a/tests/qemu-iotests/046.out
+++ b/tests/qemu-iotests/046.out
@@ -66,7 +66,7 @@
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 65536/65536 bytes at offset 2031616
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=6442450944 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == Some concurrent requests touching the same cluster ==
 blkdebug: Suspended request 'A'
diff --git a/tests/qemu-iotests/050 b/tests/qemu-iotests/050
index cdc5356..4b0a390 100755
--- a/tests/qemu-iotests/050
+++ b/tests/qemu-iotests/050
@@ -58,13 +58,13 @@
 
 TEST_IMG="$TEST_IMG_SAVE"
 
-_make_test_img -b "$TEST_IMG.old" $size
+_make_test_img -b "$TEST_IMG.old" -F $IMGFMT $size
 $QEMU_IO -c "write -z 0 1048576" "$TEST_IMG" | _filter_qemu_io
 
 echo
 echo "== Rebasing the image =="
 
-$QEMU_IMG rebase -b "$TEST_IMG.new" "$TEST_IMG"
+$QEMU_IMG rebase -b "$TEST_IMG.new" -F $IMGFMT "$TEST_IMG"
 $QEMU_IO -c "read -P 0x00 0 1048576" "$TEST_IMG" | _filter_qemu_io
 
 # success, all done
diff --git a/tests/qemu-iotests/050.out b/tests/qemu-iotests/050.out
index 3602d58..ab3daed 100644
--- a/tests/qemu-iotests/050.out
+++ b/tests/qemu-iotests/050.out
@@ -7,7 +7,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.new', fmt=IMGFMT size=10485760
 wrote 1048576/1048576 bytes at offset 0
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=10485760 backing_file=TEST_DIR/t.IMGFMT.old
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=10485760 backing_file=TEST_DIR/t.IMGFMT.old backing_fmt=IMGFMT
 wrote 1048576/1048576 bytes at offset 0
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
diff --git a/tests/qemu-iotests/051 b/tests/qemu-iotests/051
index 034d3a3..bee2607 100755
--- a/tests/qemu-iotests/051
+++ b/tests/qemu-iotests/051
@@ -70,7 +70,7 @@
 _make_test_img $size
 cp "$TEST_IMG" "$TEST_IMG.orig"
 mv "$TEST_IMG" "$TEST_IMG.base"
-_make_test_img -b "$TEST_IMG.base" $size
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $size
 
 echo
 echo === Unknown option ===
diff --git a/tests/qemu-iotests/051.out b/tests/qemu-iotests/051.out
index 554c5ca..de4771b 100644
--- a/tests/qemu-iotests/051.out
+++ b/tests/qemu-iotests/051.out
@@ -1,6 +1,6 @@
 QA output created by 051
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 === Unknown option ===
 
diff --git a/tests/qemu-iotests/051.pc.out b/tests/qemu-iotests/051.pc.out
index da8ad87..f707471 100644
--- a/tests/qemu-iotests/051.pc.out
+++ b/tests/qemu-iotests/051.pc.out
@@ -1,6 +1,6 @@
 QA output created by 051
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 === Unknown option ===
 
diff --git a/tests/qemu-iotests/056 b/tests/qemu-iotests/056
index f73fc74..052456a 100755
--- a/tests/qemu-iotests/056
+++ b/tests/qemu-iotests/056
@@ -54,7 +54,8 @@
 
     def setUp(self):
         create_image(backing_img, TestSyncModesNoneAndTop.image_len)
-        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_img('create', '-f', iotests.imgfmt,
+                 '-o', 'backing_file=%s' % backing_img, '-F', 'raw', test_img)
         qemu_io('-c', 'write -P0x41 0 512', test_img)
         qemu_io('-c', 'write -P0xd5 1M 32k', test_img)
         qemu_io('-c', 'write -P0xdc 32M 124k', test_img)
diff --git a/tests/qemu-iotests/060 b/tests/qemu-iotests/060
index 32c0ecc..94c0d5a 100755
--- a/tests/qemu-iotests/060
+++ b/tests/qemu-iotests/060
@@ -160,7 +160,7 @@
 
 $QEMU_IO -c 'write 0k 64k' "$BACKING_IMG" | _filter_qemu_io
 
-_make_test_img -b "$BACKING_IMG" 1G
+_make_test_img -b "$BACKING_IMG" -F $IMGFMT 1G
 # Write two clusters, the second one enforces creation of an L2 table after
 # the first data cluster.
 $QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out
index be5f870..e574c38 100644
--- a/tests/qemu-iotests/060.out
+++ b/tests/qemu-iotests/060.out
@@ -101,7 +101,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1073741824
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 65536/65536 bytes at offset 536870912
diff --git a/tests/qemu-iotests/061 b/tests/qemu-iotests/061
index 10eb243..08ddbdd 100755
--- a/tests/qemu-iotests/061
+++ b/tests/qemu-iotests/061
@@ -224,7 +224,7 @@
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img -o "compat=1.1" 64M
 $QEMU_IO -c "write -P 0x2a 0 128k" "$TEST_IMG.base" | _filter_qemu_io
-_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" 64M
+_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" -F $IMGFMT 64M
 $QEMU_IO -c "read -P 0x2a 0 128k" -c "write -z 0 64k" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG amend -o "compat=0.10" "$TEST_IMG"
 _check_test_img
@@ -235,7 +235,7 @@
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img -o "compat=1.1" 64M
 $QEMU_IO -c "write -P 0x2a 0 128k" "$TEST_IMG.base" | _filter_qemu_io
-_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" 64M
+_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" -F $IMGFMT 64M
 $QEMU_IO -c "write -z 0 64k" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG snapshot -c foo "$TEST_IMG"
 $QEMU_IO -c "write -P 0x42 0 128k" "$TEST_IMG" | _filter_qemu_io
@@ -251,7 +251,7 @@
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img -o "compat=1.1" 64M
 $QEMU_IO -c "write -P 0x2a 0 128k" "$TEST_IMG.base" | _filter_qemu_io
-_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" 64M
+_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" -F $IMGFMT 64M
 $QEMU_IO -c "write -z 0 128k" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG snapshot -c foo "$TEST_IMG"
 $QEMU_IMG amend -o "compat=0.10" "$TEST_IMG"
@@ -274,7 +274,7 @@
 echo "=== Testing progress report without snapshot ==="
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img -o "compat=1.1" 4G
-_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" 4G
+_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" -F $IMGFMT 4G
 $QEMU_IO -c "write -z 0  64k" \
          -c "write -z 1G 64k" \
          -c "write -z 2G 64k" \
@@ -286,7 +286,7 @@
 echo "=== Testing progress report with snapshot ==="
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img -o "compat=1.1" 4G
-_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" 4G
+_make_test_img -o "compat=1.1" -b "$TEST_IMG.base" -F $IMGFMT 4G
 $QEMU_IO -c "write -z 0  64k" \
          -c "write -z 1G 64k" \
          -c "write -z 2G 64k" \
diff --git a/tests/qemu-iotests/061.out b/tests/qemu-iotests/061.out
index 44e3c62..b2d2dfe 100644
--- a/tests/qemu-iotests/061.out
+++ b/tests/qemu-iotests/061.out
Binary files differ
diff --git a/tests/qemu-iotests/069 b/tests/qemu-iotests/069
index b997b12..a4da83b 100755
--- a/tests/qemu-iotests/069
+++ b/tests/qemu-iotests/069
@@ -46,7 +46,7 @@
 echo "=== Creating an image with a backing file and deleting that file ==="
 echo
 TEST_IMG="$TEST_IMG.base" _make_test_img $IMG_SIZE
-_make_test_img -b "$TEST_IMG.base" $IMG_SIZE
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $IMG_SIZE
 _rm_test_img "$TEST_IMG.base"
 # Just open the image and close it right again (this should print an error message)
 $QEMU_IO -c quit "$TEST_IMG" 2>&1 | _filter_testdir | _filter_imgfmt
diff --git a/tests/qemu-iotests/069.out b/tests/qemu-iotests/069.out
index c78e8c2..126b4d2 100644
--- a/tests/qemu-iotests/069.out
+++ b/tests/qemu-iotests/069.out
@@ -3,6 +3,6 @@
 === Creating an image with a backing file and deleting that file ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=131072
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 qemu-io: can't open device TEST_DIR/t.IMGFMT: Could not open backing file: Could not open 'TEST_DIR/t.IMGFMT.base': No such file or directory
 *** done
diff --git a/tests/qemu-iotests/073 b/tests/qemu-iotests/073
index 23a1bdf..1dce478 100755
--- a/tests/qemu-iotests/073
+++ b/tests/qemu-iotests/073
@@ -52,7 +52,7 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img $size
 
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 $QEMU_IO -c "write -P 0xa5 0 $size" "$TEST_IMG.base" | _filter_qemu_io
 
 echo
diff --git a/tests/qemu-iotests/073.out b/tests/qemu-iotests/073.out
index de54524..7a718b5 100644
--- a/tests/qemu-iotests/073.out
+++ b/tests/qemu-iotests/073.out
@@ -2,7 +2,7 @@
 
 == creating backing file ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
diff --git a/tests/qemu-iotests/082 b/tests/qemu-iotests/082
index 1998965..2135581 100755
--- a/tests/qemu-iotests/082
+++ b/tests/qemu-iotests/082
@@ -84,8 +84,10 @@
 run_qemu_img create -f $IMGFMT -o cluster_size=4k -o \? "$TEST_IMG" $size
 
 # Looks like a help option, but is part of the backing file name
-run_qemu_img create -f $IMGFMT -u -o backing_file="$TEST_IMG",,help "$TEST_IMG" $size
-run_qemu_img create -f $IMGFMT -u -o backing_file="$TEST_IMG",,\? "$TEST_IMG" $size
+run_qemu_img create -f $IMGFMT -u -o backing_file="$TEST_IMG",,help \
+    -F $IMGFMT "$TEST_IMG" $size
+run_qemu_img create -f $IMGFMT -u -o backing_file="$TEST_IMG",,\? \
+    -F $IMGFMT "$TEST_IMG" $size
 
 # Try to trick qemu-img into creating escaped commas
 run_qemu_img create -f $IMGFMT -o backing_file="$TEST_IMG", -o help "$TEST_IMG" $size
@@ -141,8 +143,8 @@
 run_qemu_img convert -O $IMGFMT -o cluster_size=4k -o \? "$TEST_IMG" "$TEST_IMG".base
 
 # Looks like a help option, but is part of the backing file name
-run_qemu_img convert -O $IMGFMT -o backing_file="$TEST_IMG",,help "$TEST_IMG" "$TEST_IMG".base
-run_qemu_img convert -O $IMGFMT -o backing_file="$TEST_IMG",,\? "$TEST_IMG" "$TEST_IMG".base
+run_qemu_img convert -O $IMGFMT -o backing_fmt=$IMGFMT,backing_file="$TEST_IMG",,help "$TEST_IMG" "$TEST_IMG".base
+run_qemu_img convert -O $IMGFMT -o backing_fmt=$IMGFMT,backing_file="$TEST_IMG",,\? "$TEST_IMG" "$TEST_IMG".base
 
 # Try to trick qemu-img into creating escaped commas
 run_qemu_img convert -O $IMGFMT -o backing_file="$TEST_IMG", -o help "$TEST_IMG" "$TEST_IMG".base
diff --git a/tests/qemu-iotests/082.out b/tests/qemu-iotests/082.out
index a38a26f..1728aff 100644
--- a/tests/qemu-iotests/082.out
+++ b/tests/qemu-iotests/082.out
@@ -244,11 +244,11 @@
   refcount_bits=<num>    - Width of a reference count entry in bits
   size=<size>            - Virtual disk size
 
-Testing: create -f qcow2 -u -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 128M
-Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 compression_type=zlib size=134217728 backing_file=TEST_DIR/t.qcow2,,help lazy_refcounts=off refcount_bits=16
+Testing: create -f qcow2 -u -o backing_file=TEST_DIR/t.qcow2,,help -F qcow2 TEST_DIR/t.qcow2 128M
+Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 compression_type=zlib size=134217728 backing_file=TEST_DIR/t.qcow2,,help backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
-Testing: create -f qcow2 -u -o backing_file=TEST_DIR/t.qcow2,,? TEST_DIR/t.qcow2 128M
-Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 compression_type=zlib size=134217728 backing_file=TEST_DIR/t.qcow2,,? lazy_refcounts=off refcount_bits=16
+Testing: create -f qcow2 -u -o backing_file=TEST_DIR/t.qcow2,,? -F qcow2 TEST_DIR/t.qcow2 128M
+Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 cluster_size=65536 compression_type=zlib size=134217728 backing_file=TEST_DIR/t.qcow2,,? backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 Testing: create -f qcow2 -o backing_file=TEST_DIR/t.qcow2, -o help TEST_DIR/t.qcow2 128M
 qemu-img: Invalid option list: backing_file=TEST_DIR/t.qcow2,
@@ -543,10 +543,10 @@
   refcount_bits=<num>    - Width of a reference count entry in bits
   size=<size>            - Virtual disk size
 
-Testing: convert -O qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
+Testing: convert -O qcow2 -o backing_fmt=qcow2,backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 qemu-img: Could not open 'TEST_DIR/t.qcow2.base': Could not open backing file: Could not open 'TEST_DIR/t.qcow2,help': No such file or directory
 
-Testing: convert -O qcow2 -o backing_file=TEST_DIR/t.qcow2,,? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
+Testing: convert -O qcow2 -o backing_fmt=qcow2,backing_file=TEST_DIR/t.qcow2,,? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 qemu-img: Could not open 'TEST_DIR/t.qcow2.base': Could not open backing file: Could not open 'TEST_DIR/t.qcow2,?': No such file or directory
 
 Testing: convert -O qcow2 -o backing_file=TEST_DIR/t.qcow2, -o help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
diff --git a/tests/qemu-iotests/085 b/tests/qemu-iotests/085
index dd3c993..e99eb44 100755
--- a/tests/qemu-iotests/085
+++ b/tests/qemu-iotests/085
@@ -106,7 +106,7 @@
 {
     base_image="${TEST_DIR}/$((${1}-1))-${snapshot_virt0}"
     snapshot_file="${TEST_DIR}/${1}-${snapshot_virt0}"
-    TEST_IMG=$snapshot_file _make_test_img -u -b "${base_image}" "$size"
+    TEST_IMG=$snapshot_file _make_test_img -u -b "${base_image}" -F $IMGFMT "$size"
     do_blockdev_add "$1" "'backing': null, " "${snapshot_file}"
 }
 
@@ -225,7 +225,7 @@
 SNAPSHOTS=$((${SNAPSHOTS}+1))
 
 TEST_IMG="$TEST_IMG.base" _make_test_img "$size"
-_make_test_img -b "${TEST_IMG}.base" "$size"
+_make_test_img -b "${TEST_IMG}.base" -F $IMGFMT "$size"
 do_blockdev_add ${SNAPSHOTS} "" "${TEST_IMG}"
 blockdev_snapshot ${SNAPSHOTS} error
 
diff --git a/tests/qemu-iotests/085.out b/tests/qemu-iotests/085.out
index d68c06e..700658d 100644
--- a/tests/qemu-iotests/085.out
+++ b/tests/qemu-iotests/085.out
@@ -68,12 +68,12 @@
 
 === Create a couple of snapshots using blockdev-snapshot ===
 
-Formatting 'TEST_DIR/11-snapshot-v0.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/10-snapshot-v0.IMGFMT
+Formatting 'TEST_DIR/11-snapshot-v0.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/10-snapshot-v0.IMGFMT backing_fmt=IMGFMT
 { 'execute': 'blockdev-add', 'arguments': { 'driver': 'IMGFMT', 'node-name': 'snap_11', 'backing': null, 'file': { 'driver': 'file', 'filename': 'TEST_DIR/11-snapshot-v0.IMGFMT', 'node-name': 'file_11' } } }
 {"return": {}}
 { 'execute': 'blockdev-snapshot', 'arguments': { 'node': 'virtio0', 'overlay':'snap_11' } }
 {"return": {}}
-Formatting 'TEST_DIR/12-snapshot-v0.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/11-snapshot-v0.IMGFMT
+Formatting 'TEST_DIR/12-snapshot-v0.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/11-snapshot-v0.IMGFMT backing_fmt=IMGFMT
 { 'execute': 'blockdev-add', 'arguments': { 'driver': 'IMGFMT', 'node-name': 'snap_12', 'backing': null, 'file': { 'driver': 'file', 'filename': 'TEST_DIR/12-snapshot-v0.IMGFMT', 'node-name': 'file_12' } } }
 {"return": {}}
 { 'execute': 'blockdev-snapshot', 'arguments': { 'node': 'virtio0', 'overlay':'snap_12' } }
@@ -101,7 +101,7 @@
 === Invalid command - snapshot node has a backing image ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 { 'execute': 'blockdev-add', 'arguments': { 'driver': 'IMGFMT', 'node-name': 'snap_13', 'file': { 'driver': 'file', 'filename': 'TEST_DIR/t.IMGFMT', 'node-name': 'file_13' } } }
 {"return": {}}
 { 'execute': 'blockdev-snapshot', 'arguments': { 'node': 'virtio0', 'overlay':'snap_13' } }
diff --git a/tests/qemu-iotests/089 b/tests/qemu-iotests/089
index 059ad75..66c5415 100755
--- a/tests/qemu-iotests/089
+++ b/tests/qemu-iotests/089
@@ -84,7 +84,7 @@
 echo "=== Testing correct handling of 'backing':null ==="
 echo
 
-_make_test_img -b "$TEST_IMG.base" $IMG_SIZE
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $IMG_SIZE
 
 # This should read 42
 $QEMU_IO -c 'read -P 42 0 512' "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/089.out b/tests/qemu-iotests/089.out
index 20c8ce8..15682c2 100644
--- a/tests/qemu-iotests/089.out
+++ b/tests/qemu-iotests/089.out
@@ -21,7 +21,7 @@
 
 === Testing correct handling of 'backing':null ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 read 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 read 512/512 bytes at offset 0
diff --git a/tests/qemu-iotests/095 b/tests/qemu-iotests/095
index 155ae86..77a5f0f 100755
--- a/tests/qemu-iotests/095
+++ b/tests/qemu-iotests/095
@@ -51,9 +51,9 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img $size_smaller
 
-TEST_IMG="$TEST_IMG.snp1" _make_test_img -b "$TEST_IMG.base" $size_larger
+TEST_IMG="$TEST_IMG.snp1" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT $size_larger
 
-_make_test_img -b "${TEST_IMG}.snp1" $size_larger
+_make_test_img -b "${TEST_IMG}.snp1" -F $IMGFMT $size_larger
 
 echo
 echo "=== Base image info before commit and resize ==="
diff --git a/tests/qemu-iotests/095.out b/tests/qemu-iotests/095.out
index 614e5cc..e66ced5 100644
--- a/tests/qemu-iotests/095.out
+++ b/tests/qemu-iotests/095.out
@@ -1,7 +1,7 @@
 QA output created by 095
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=5242880
-Formatting 'TEST_DIR/t.IMGFMT.snp1', fmt=IMGFMT size=104857600 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=104857600 backing_file=TEST_DIR/t.IMGFMT.snp1
+Formatting 'TEST_DIR/t.IMGFMT.snp1', fmt=IMGFMT size=104857600 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=104857600 backing_file=TEST_DIR/t.IMGFMT.snp1 backing_fmt=IMGFMT
 
 === Base image info before commit and resize ===
 image: TEST_DIR/t.IMGFMT.base
diff --git a/tests/qemu-iotests/097 b/tests/qemu-iotests/097
index 690f3d3..d910a8b 100755
--- a/tests/qemu-iotests/097
+++ b/tests/qemu-iotests/097
@@ -67,8 +67,8 @@
 
 len=$((2100 * 1024 * 1024 + 512)) # larger than 2G, and not cluster aligned
 TEST_IMG="$TEST_IMG.base" _make_test_img $len
-TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" $len
-_make_test_img -b "$TEST_IMG.itmd" $len
+TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT $len
+_make_test_img -b "$TEST_IMG.itmd" -F $IMGFMT $len
 
 $QEMU_IO -c "write -P 1 0x7ffd0000 192k" "$TEST_IMG.base" | _filter_qemu_io
 $QEMU_IO -c "write -P 2 0x7ffe0000 128k" "$TEST_IMG.itmd" | _filter_qemu_io
diff --git a/tests/qemu-iotests/097.out b/tests/qemu-iotests/097.out
index f6705a1..3038dda 100644
--- a/tests/qemu-iotests/097.out
+++ b/tests/qemu-iotests/097.out
@@ -3,8 +3,8 @@
 === Test pass 0 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -40,8 +40,8 @@
 === Test pass 1 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -78,8 +78,8 @@
 === Test pass 2 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -116,8 +116,8 @@
 === Test pass 3 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
diff --git a/tests/qemu-iotests/098 b/tests/qemu-iotests/098
index 1e29d96..f2ccdd7 100755
--- a/tests/qemu-iotests/098
+++ b/tests/qemu-iotests/098
@@ -52,7 +52,7 @@
 echo
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-_make_test_img -b "$TEST_IMG.base" 64M
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT 64M
 
 # Some data that can be leaked when emptying the top image
 $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/098.out b/tests/qemu-iotests/098.out
index 23cf371..6c73dd0 100644
--- a/tests/qemu-iotests/098.out
+++ b/tests/qemu-iotests/098.out
@@ -3,7 +3,7 @@
 === l1_update ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Failed to empty blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
@@ -12,7 +12,7 @@
 === empty_image_prepare ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Failed to empty blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
@@ -25,7 +25,7 @@
 === reftable_update ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Failed to empty blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
@@ -39,7 +39,7 @@
 === refblock_alloc ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Failed to empty blkdebug:TEST_DIR/blkdebug.conf:TEST_DIR/t.IMGFMT: Input/output error
diff --git a/tests/qemu-iotests/110 b/tests/qemu-iotests/110
index 139c02c..f1813d0 100755
--- a/tests/qemu-iotests/110
+++ b/tests/qemu-iotests/110
@@ -50,7 +50,7 @@
 echo
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-_make_test_img -b "$TEST_IMG_REL.base" 64M
+_make_test_img -b "$TEST_IMG_REL.base" -F $IMGFMT 64M
 # qemu should be able to reconstruct the filename, so relative backing names
 # should work
 # (We have to filter the backing file format because vmdk always
@@ -91,7 +91,7 @@
 echo
 
 # omit the image size; it should work anyway
-_make_test_img -b "$TEST_IMG_REL.base"
+_make_test_img -b "$TEST_IMG_REL.base" -F $IMGFMT
 
 echo
 echo '=== Nodes without a common directory ==='
diff --git a/tests/qemu-iotests/110.out b/tests/qemu-iotests/110.out
index f835553..cf8f6c0 100644
--- a/tests/qemu-iotests/110.out
+++ b/tests/qemu-iotests/110.out
@@ -3,7 +3,7 @@
 === Reconstructable filename ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=t.IMGFMT.base backing_fmt=IMGFMT
 image: TEST_DIR/t.IMGFMT
 file format: IMGFMT
 virtual size: 64 MiB (67108864 bytes)
@@ -18,7 +18,7 @@
 
 === Backing name is always relative to the backed image ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=t.IMGFMT.base backing_fmt=IMGFMT
 
 === Nodes without a common directory ===
 
diff --git a/tests/qemu-iotests/122 b/tests/qemu-iotests/122
index 2dc16b2..dfd1cd0 100755
--- a/tests/qemu-iotests/122
+++ b/tests/qemu-iotests/122
@@ -52,9 +52,10 @@
 echo "=== Check allocation status regression with -B ==="
 echo
 
-_make_test_img -b "$TEST_IMG".base
+_make_test_img -b "$TEST_IMG".base -F $IMGFMT
 $QEMU_IO -c "write -P 0x22 0 3M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base "$TEST_IMG" "$TEST_IMG".orig
+$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base \
+    -o backing_fmt=$IMGFMT "$TEST_IMG" "$TEST_IMG".orig
 $QEMU_IMG map "$TEST_IMG".orig | _filter_qemu_img_map
 
 
@@ -62,18 +63,22 @@
 echo "=== Check that zero clusters are kept in overlay ==="
 echo
 
-_make_test_img -b "$TEST_IMG".base
+_make_test_img -b "$TEST_IMG".base -F $IMGFMT
 
 $QEMU_IO -c "write -P 0 0 3M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base "$TEST_IMG" "$TEST_IMG".orig
+$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base -o backing_fmt=$IMGFMT \
+    "$TEST_IMG" "$TEST_IMG".orig
 $QEMU_IO -c "read -P 0 0 3M" "$TEST_IMG".orig 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IMG convert -O $IMGFMT -c -B "$TEST_IMG".base "$TEST_IMG" "$TEST_IMG".orig
+$QEMU_IMG convert -O $IMGFMT -c -B "$TEST_IMG".base -o backing_fmt=$IMGFMT \
+    "$TEST_IMG" "$TEST_IMG".orig
 $QEMU_IO -c "read -P 0 0 3M" "$TEST_IMG".orig 2>&1 | _filter_qemu_io | _filter_testdir
 
 $QEMU_IO -c "write -z 0 3M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base "$TEST_IMG" "$TEST_IMG".orig
+$QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base -o backing_fmt=$IMGFMT \
+    "$TEST_IMG" "$TEST_IMG".orig
 $QEMU_IO -c "read -P 0 0 3M" "$TEST_IMG".orig 2>&1 | _filter_qemu_io | _filter_testdir
-$QEMU_IMG convert -O $IMGFMT -c -B "$TEST_IMG".base "$TEST_IMG" "$TEST_IMG".orig
+$QEMU_IMG convert -O $IMGFMT -c -B "$TEST_IMG".base -o backing_fmt=$IMGFMT \
+    "$TEST_IMG" "$TEST_IMG".orig
 $QEMU_IO -c "read -P 0 0 3M" "$TEST_IMG".orig 2>&1 | _filter_qemu_io | _filter_testdir
 
 
@@ -94,11 +99,11 @@
 # We do not want such a zero write, however, because we are past the
 # end of the backing file on the target as well, so we do not need to
 # write anything there.
-_make_test_img -b "$TEST_IMG".base 768M
+_make_test_img -b "$TEST_IMG".base 768M -F $IMGFMT
 
 # Use compat=0.10 as the output so there is no zero cluster support
 $QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base -o compat=0.10 \
-    "$TEST_IMG" "$TEST_IMG".orig
+    -o backing_fmt=$IMGFMT "$TEST_IMG" "$TEST_IMG".orig
 # See that nothing has been allocated past 64M
 $QEMU_IMG map "$TEST_IMG".orig | _filter_qemu_img_map
 
@@ -110,7 +115,7 @@
 $QEMU_IO -c 'write -P 0x22 600M 1M' "$TEST_IMG" 2>&1 | _filter_qemu_io
 
 $QEMU_IMG convert -O $IMGFMT -B "$TEST_IMG".base -o compat=0.10 \
-    "$TEST_IMG" "$TEST_IMG".orig
+    -o backing_fmt=$IMGFMT "$TEST_IMG" "$TEST_IMG".orig
 
 $QEMU_IMG map "$TEST_IMG".orig | _filter_qemu_img_map
 $QEMU_IO -c 'read -P 0x11 255M 1M' \
@@ -199,7 +204,7 @@
 TEST_IMG="$TEST_IMG".base _make_test_img 64M
 $QEMU_IO -c "write -P 0x11 0 32M" "$TEST_IMG".base 2>&1 | _filter_qemu_io | _filter_testdir
 
-_make_test_img -b "$TEST_IMG".base 64M
+_make_test_img -b "$TEST_IMG".base 64M -F $IMGFMT
 $QEMU_IO -c "write -P 0x22 0 3M" "$TEST_IMG" 2>&1 | _filter_qemu_io | _filter_testdir
 
 echo
diff --git a/tests/qemu-iotests/122.out b/tests/qemu-iotests/122.out
index c2e154a..f1f195e 100644
--- a/tests/qemu-iotests/122.out
+++ b/tests/qemu-iotests/122.out
@@ -5,7 +5,7 @@
 
 === Check allocation status regression with -B ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 3145728/3145728 bytes at offset 0
 3 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Offset          Length          File
@@ -14,7 +14,7 @@
 
 === Check that zero clusters are kept in overlay ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 3145728/3145728 bytes at offset 0
 3 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 read 3145728/3145728 bytes at offset 0
@@ -31,7 +31,7 @@
 === Converting to an overlay larger than its backing file ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=268435456
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=805306368 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=805306368 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Offset          Length          File
 
 wrote 1048576/1048576 bytes at offset 267386880
@@ -141,7 +141,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
 wrote 33554432/33554432 bytes at offset 0
 32 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 3145728/3145728 bytes at offset 0
 3 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
diff --git a/tests/qemu-iotests/126 b/tests/qemu-iotests/126
index b7fce1e..dd5a211 100755
--- a/tests/qemu-iotests/126
+++ b/tests/qemu-iotests/126
@@ -61,7 +61,7 @@
 TOP_IMG="$TEST_DIR/image:top.$IMGFMT"
 
 TEST_IMG=$BASE_IMG _make_test_img 64M
-TEST_IMG=$TOP_IMG _make_test_img -b ./image:base.$IMGFMT
+TEST_IMG=$TOP_IMG _make_test_img -b ./image:base.$IMGFMT -F $IMGFMT
 
 # (1) The default cluster size depends on the image format
 # (2) vmdk only supports vmdk backing files, so it always reports the
@@ -82,7 +82,7 @@
 TOP_IMG="file:image:top.$IMGFMT"
 
 TEST_IMG=$BASE_IMG _make_test_img 64M
-TEST_IMG=$TOP_IMG _make_test_img -b "$BASE_IMG"
+TEST_IMG=$TOP_IMG _make_test_img -b "$BASE_IMG" -F $IMGFMT
 
 TEST_IMG=$TOP_IMG _img_info | grep -ve 'cluster_size' -e 'backing file format'
 
diff --git a/tests/qemu-iotests/126.out b/tests/qemu-iotests/126.out
index e3c4d61..7d66346 100644
--- a/tests/qemu-iotests/126.out
+++ b/tests/qemu-iotests/126.out
@@ -8,14 +8,14 @@
 === Testing relative backing filename resolution ===
 
 Formatting 'TEST_DIR/image:base.IMGFMT', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=./image:base.IMGFMT
+Formatting 'TEST_DIR/image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=./image:base.IMGFMT backing_fmt=IMGFMT
 image: TEST_DIR/image:top.IMGFMT
 file format: IMGFMT
 virtual size: 64 MiB (67108864 bytes)
 backing file: ./image:base.IMGFMT (actual path: TEST_DIR/./image:base.IMGFMT)
 
 Formatting 'base.IMGFMT', fmt=IMGFMT size=67108864
-Formatting 'file:image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=base.IMGFMT
+Formatting 'file:image:top.IMGFMT', fmt=IMGFMT size=67108864 backing_file=base.IMGFMT backing_fmt=IMGFMT
 image: ./image:top.IMGFMT
 file format: IMGFMT
 virtual size: 64 MiB (67108864 bytes)
diff --git a/tests/qemu-iotests/127 b/tests/qemu-iotests/127
index a4fc866..e2ac2f5 100755
--- a/tests/qemu-iotests/127
+++ b/tests/qemu-iotests/127
@@ -48,8 +48,8 @@
 IMG_SIZE=64K
 
 _make_test_img $IMG_SIZE
-TEST_IMG="$TEST_IMG.overlay0" _make_test_img -b "$TEST_IMG" $IMG_SIZE
-TEST_IMG="$TEST_IMG.overlay1" _make_test_img -b "$TEST_IMG" $IMG_SIZE
+TEST_IMG="$TEST_IMG.overlay0" _make_test_img -b "$TEST_IMG" -F $IMGFMT $IMG_SIZE
+TEST_IMG="$TEST_IMG.overlay1" _make_test_img -b "$TEST_IMG" -F $IMGFMT $IMG_SIZE
 
 # So that we actually have something to mirror and the job does not return
 # immediately (which may be bad because then we cannot know whether the
diff --git a/tests/qemu-iotests/127.out b/tests/qemu-iotests/127.out
index 623d52b..efd6cb3 100644
--- a/tests/qemu-iotests/127.out
+++ b/tests/qemu-iotests/127.out
@@ -1,7 +1,7 @@
 QA output created by 127
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=65536
-Formatting 'TEST_DIR/t.IMGFMT.overlay0', fmt=IMGFMT size=65536 backing_file=TEST_DIR/t.IMGFMT
-Formatting 'TEST_DIR/t.IMGFMT.overlay1', fmt=IMGFMT size=65536 backing_file=TEST_DIR/t.IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.overlay0', fmt=IMGFMT size=65536 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.overlay1', fmt=IMGFMT size=65536 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
 wrote 42/42 bytes at offset 0
 42 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 { 'execute': 'qmp_capabilities' }
diff --git a/tests/qemu-iotests/129 b/tests/qemu-iotests/129
index b0da4a5..0e13244 100755
--- a/tests/qemu-iotests/129
+++ b/tests/qemu-iotests/129
@@ -29,7 +29,8 @@
 
     def setUp(self):
         iotests.qemu_img('create', '-f', iotests.imgfmt, self.base_img, "1G")
-        iotests.qemu_img('create', '-f', iotests.imgfmt, self.test_img, "-b", self.base_img)
+        iotests.qemu_img('create', '-f', iotests.imgfmt, self.test_img,
+                         "-b", self.base_img, '-F', iotests.imgfmt)
         iotests.qemu_io('-f', iotests.imgfmt, '-c', 'write -P0x5d 1M 128M', self.test_img)
         self.vm = iotests.VM().add_drive(self.test_img)
         self.vm.launch()
diff --git a/tests/qemu-iotests/133 b/tests/qemu-iotests/133
index 6f7cacc..4070fd9 100755
--- a/tests/qemu-iotests/133
+++ b/tests/qemu-iotests/133
@@ -40,7 +40,7 @@
 _supported_proto file
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 echo
 echo "=== Check that node-name can't be changed ==="
diff --git a/tests/qemu-iotests/133.out b/tests/qemu-iotests/133.out
index 1491ef4..d70c2e8 100644
--- a/tests/qemu-iotests/133.out
+++ b/tests/qemu-iotests/133.out
@@ -1,6 +1,6 @@
 QA output created by 133
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 === Check that node-name can't be changed ===
 
diff --git a/tests/qemu-iotests/139 b/tests/qemu-iotests/139
index 7120d31..1452fd2 100755
--- a/tests/qemu-iotests/139
+++ b/tests/qemu-iotests/139
@@ -71,7 +71,7 @@
     def addBlockDriverStateOverlay(self, node):
         self.checkBlockDriverState(node, False)
         iotests.qemu_img('create', '-u', '-f', iotests.imgfmt,
-                         '-b', base_img, new_img, '1M')
+                         '-b', base_img, '-F', iotests.imgfmt, new_img, '1M')
         opts = {'driver': iotests.imgfmt,
                 'node-name': node,
                 'backing': None,
diff --git a/tests/qemu-iotests/141 b/tests/qemu-iotests/141
index 5192d25..21aa0b4 100755
--- a/tests/qemu-iotests/141
+++ b/tests/qemu-iotests/141
@@ -89,8 +89,8 @@
 
 
 TEST_IMG="$TEST_DIR/b.$IMGFMT" _make_test_img 1M
-TEST_IMG="$TEST_DIR/m.$IMGFMT" _make_test_img -b "$TEST_DIR/b.$IMGFMT" 1M
-_make_test_img -b "$TEST_DIR/m.$IMGFMT" 1M
+TEST_IMG="$TEST_DIR/m.$IMGFMT" _make_test_img -b "$TEST_DIR/b.$IMGFMT" -F $IMGFMT 1M
+_make_test_img -b "$TEST_DIR/m.$IMGFMT" 1M -F $IMGFMT
 
 _launch_qemu -nodefaults
 
diff --git a/tests/qemu-iotests/141.out b/tests/qemu-iotests/141.out
index 263b680..08e0aec 100644
--- a/tests/qemu-iotests/141.out
+++ b/tests/qemu-iotests/141.out
@@ -1,7 +1,7 @@
 QA output created by 141
 Formatting 'TEST_DIR/b.IMGFMT', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/m.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/b.IMGFMT
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/m.IMGFMT
+Formatting 'TEST_DIR/m.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/b.IMGFMT backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/m.IMGFMT backing_fmt=IMGFMT
 {'execute': 'qmp_capabilities'}
 {"return": {}}
 
diff --git a/tests/qemu-iotests/142 b/tests/qemu-iotests/142
index daefcba..69fd10e 100755
--- a/tests/qemu-iotests/142
+++ b/tests/qemu-iotests/142
@@ -67,7 +67,7 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img $size
 TEST_IMG="$TEST_IMG.snap" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base" $size
+_make_test_img -b "$TEST_IMG.base" $size -F $IMGFMT
 
 echo
 echo === Simple test for all cache modes ===
diff --git a/tests/qemu-iotests/142.out b/tests/qemu-iotests/142.out
index 3667e38..a92b948 100644
--- a/tests/qemu-iotests/142.out
+++ b/tests/qemu-iotests/142.out
@@ -1,7 +1,7 @@
 QA output created by 142
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
 Formatting 'TEST_DIR/t.IMGFMT.snap', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 === Simple test for all cache modes ===
 
diff --git a/tests/qemu-iotests/153 b/tests/qemu-iotests/153
index 11e3d28..34045ea 100755
--- a/tests/qemu-iotests/153
+++ b/tests/qemu-iotests/153
@@ -94,7 +94,7 @@
 
     echo
     echo "== Creating test image =="
-    _make_test_img -b "${TEST_IMG}.base"
+    _make_test_img -b "${TEST_IMG}.base" -F $IMGFMT
 
     echo
     echo "== Launching QEMU, opts: '$opts1' =="
@@ -125,7 +125,7 @@
         _run_cmd $QEMU_IMG amend -o "size=$size" $L "${TEST_IMG}"
         _run_cmd $QEMU_IMG commit      $L "${TEST_IMG}"
         _run_cmd $QEMU_IMG resize      $L "${TEST_IMG}" $size
-        _run_cmd $QEMU_IMG rebase      $L "${TEST_IMG}" -b "${TEST_IMG}.base"
+        _run_cmd $QEMU_IMG rebase      $L "${TEST_IMG}" -b "${TEST_IMG}.base" -F $IMGFMT
         _run_cmd $QEMU_IMG snapshot -l $L "${TEST_IMG}"
         _run_cmd $QEMU_IMG convert     $L "${TEST_IMG}" "${TEST_IMG}.convert"
         _run_cmd $QEMU_IMG dd          $L if="${TEST_IMG}" of="${TEST_IMG}.convert" bs=512 count=1
@@ -135,7 +135,7 @@
         # qemu-img create does not support -U
         if [ -z "$L" ]; then
             _run_cmd $QEMU_IMG create -f $IMGFMT "${TEST_IMG}" \
-                                      -b ${TEST_IMG}.base
+                                      -b ${TEST_IMG}.base -F $IMGFMT
             # Read the file format.  It used to be the case that
             # file-posix simply truncated the file, but the qcow2
             # driver then failed to format it because it was unable
@@ -167,9 +167,9 @@
 
 echo
 echo "== Creating ${TEST_IMG}.[abc] ==" | _filter_testdir
-$QEMU_IMG create -f qcow2 "${TEST_IMG}.a" -b "${TEST_IMG}" | _filter_img_create
-$QEMU_IMG create -f qcow2 "${TEST_IMG}.b" -b "${TEST_IMG}" | _filter_img_create
-$QEMU_IMG create -f qcow2 "${TEST_IMG}.c" -b "${TEST_IMG}.b" \
+$QEMU_IMG create -f qcow2 "${TEST_IMG}.a" -b "${TEST_IMG}" -F $IMGFMT | _filter_img_create
+$QEMU_IMG create -f qcow2 "${TEST_IMG}.b" -b "${TEST_IMG}" -F $IMGFMT | _filter_img_create
+$QEMU_IMG create -f qcow2 "${TEST_IMG}.c" -b "${TEST_IMG}.b" -F $IMGFMT \
     | _filter_img_create
 
 echo
@@ -218,7 +218,7 @@
 _run_cmd $QEMU_IO "${TEST_IMG}" -c 'write 0 512'
 
 echo "Creating overlay with qemu-img when the guest is running should be allowed"
-_run_cmd $QEMU_IMG create -f $IMGFMT -b "${TEST_IMG}" "${TEST_IMG}.overlay"
+_run_cmd $QEMU_IMG create -f $IMGFMT -b "${TEST_IMG}" -F $IMGFMT "${TEST_IMG}.overlay"
 
 echo "== Closing an image should unlock it =="
 _send_qemu_cmd $QEMU_HANDLE \
diff --git a/tests/qemu-iotests/153.out b/tests/qemu-iotests/153.out
index b2a90ca..8a79e1e 100644
--- a/tests/qemu-iotests/153.out
+++ b/tests/qemu-iotests/153.out
@@ -6,7 +6,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=33554432
 
 == Creating test image ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == Launching QEMU, opts: '' ==
 
@@ -68,7 +68,7 @@
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
-_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
@@ -92,10 +92,11 @@
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
-_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: TEST_DIR/t.qcow2: Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 file format: IMGFMT
+backing file format: IMGFMT
 
 == Running utility commands -U ==
 
@@ -130,7 +131,7 @@
 qemu-img: unrecognized option '-U'
 Try 'qemu-img --help' for more information
 
-_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
@@ -152,7 +153,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=33554432
 
 == Creating test image ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == Launching QEMU, opts: 'read-only=on' ==
 
@@ -199,7 +200,7 @@
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
-_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
@@ -215,10 +216,11 @@
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
-_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: TEST_DIR/t.qcow2: Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 file format: IMGFMT
+backing file format: IMGFMT
 
 == Running utility commands -U ==
 
@@ -253,7 +255,7 @@
 qemu-img: unrecognized option '-U'
 Try 'qemu-img --help' for more information
 
-_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 qemu-img: Could not open 'TEST_DIR/t.qcow2': Failed to get "write" lock
 Is another process using the image [TEST_DIR/t.qcow2]?
 
@@ -275,7 +277,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=33554432
 
 == Creating test image ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == Launching QEMU, opts: 'read-only=on,force-share=on' ==
 
@@ -309,7 +311,7 @@
 
 _qemu_img_wrapper resize TEST_DIR/t.qcow2 32M
 
-_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 
 _qemu_img_wrapper snapshot -l TEST_DIR/t.qcow2
 
@@ -321,8 +323,9 @@
 
 _qemu_img_wrapper bench -w -c 1 TEST_DIR/t.qcow2
 
-_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper create -f qcow2 TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 file format: IMGFMT
+backing file format: IMGFMT
 
 == Running utility commands -U ==
 
@@ -357,7 +360,7 @@
 qemu-img: unrecognized option '-U'
 Try 'qemu-img --help' for more information
 
-_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base
+_qemu_img_wrapper rebase -U TEST_DIR/t.qcow2 -b TEST_DIR/t.qcow2.base -F qcow2
 
 _qemu_img_wrapper snapshot -l -U TEST_DIR/t.qcow2
 
@@ -398,9 +401,9 @@
 == Two devices with the same image (read-only=on,force-share=on - read-only=on,force-share=on) ==
 
 == Creating TEST_DIR/t.qcow2.[abc] ==
-Formatting 'TEST_DIR/t.IMGFMT.a', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT
-Formatting 'TEST_DIR/t.IMGFMT.b', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT
-Formatting 'TEST_DIR/t.IMGFMT.c', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.b
+Formatting 'TEST_DIR/t.IMGFMT.a', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.b', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.c', fmt=IMGFMT size=33554432 backing_file=TEST_DIR/t.IMGFMT.b backing_fmt=IMGFMT
 
 == Two devices sharing the same file in backing chain ==
 
@@ -430,7 +433,7 @@
 Is another process using the image [TEST_DIR/t.qcow2]?
 Creating overlay with qemu-img when the guest is running should be allowed
 
-_qemu_img_wrapper create -f qcow2 -b TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.overlay
+_qemu_img_wrapper create -f qcow2 -b TEST_DIR/t.qcow2 -F qcow2 TEST_DIR/t.qcow2.overlay
 == Closing an image should unlock it ==
 { 'execute': 'human-monitor-command', 'arguments': { 'command-line': 'drive_del d0' } }
 {"return": ""}
diff --git a/tests/qemu-iotests/154 b/tests/qemu-iotests/154
index d68f66b..7f1c0d9 100755
--- a/tests/qemu-iotests/154
+++ b/tests/qemu-iotests/154
@@ -50,7 +50,7 @@
 echo == backing file contains zeros ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Make sure that the whole cluster is allocated even for partial write_zeroes
 # when the backing file contains zeros
@@ -74,7 +74,7 @@
 echo == backing file contains non-zero data before write_zeroes ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Single cluster; non-zero data at the cluster start
 # ... | XX -- 00 -- | ...
@@ -97,7 +97,7 @@
 echo == backing file contains non-zero data after write_zeroes ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Single cluster; non-zero data directly after request
 # ... | -- 00 XX -- | ...
@@ -120,7 +120,7 @@
 echo == write_zeroes covers non-zero data ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # non-zero data at front of request
 # Backing file: -- XX -- --
@@ -160,7 +160,7 @@
 echo == spanning two clusters, non-zero before request ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Two clusters; non-zero data before request:
 # 1. At cluster start:          32k: XX -- -- 00 | 00 -- -- --
@@ -190,7 +190,7 @@
 echo == spanning two clusters, non-zero after request ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Two clusters; non-zero data after request:
 # 1. Directly after request:    32k: -- -- -- 00 | 00 XX -- --
@@ -220,7 +220,7 @@
 echo == spanning two clusters, partially overwriting backing file ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Backing file: -- -- XX XX | XX XX -- --
 # Active layer: -- -- XX 00 | 00 XX -- --
@@ -239,7 +239,7 @@
 echo == spanning multiple clusters, non-zero in first cluster ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Backing file: 64k: XX XX -- -- | -- -- -- -- | -- -- -- --
 # Active layer: 64k: XX XX 00 00 | 00 00 00 00 | 00 -- -- --
@@ -255,7 +255,7 @@
 echo == spanning multiple clusters, non-zero in intermediate cluster ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Backing file: 64k: -- -- -- -- | -- XX XX -- | -- -- -- --
 # Active layer: 64k: -- -- 00 00 | 00 00 00 00 | 00 -- -- --
@@ -270,7 +270,7 @@
 echo == spanning multiple clusters, non-zero in final cluster ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Backing file: 64k: -- -- -- -- | -- -- -- -- | -- -- XX XX
 # Active layer: 64k: -- -- 00 00 | 00 00 00 00 | 00 -- XX XX
@@ -286,7 +286,7 @@
 echo == spanning multiple clusters, partially overwriting backing file ==
 
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Backing file: 64k: -- XX XX XX | XX XX XX XX | XX XX XX --
 # Active layer: 64k: -- XX 00 00 | 00 00 00 00 | 00 XX XX --
@@ -338,7 +338,7 @@
 # Write at the front: sector-wise, the request is:
 # backing: 128m... | -- --
 # active:  128m... | 00 -- -- --
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $size 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -346,7 +346,7 @@
 # Write at the back: sector-wise, the request is:
 # backing: 128m... | -- --
 # active:  128m... | -- -- -- 00
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $((size + 1536)) 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -354,7 +354,7 @@
 # Write at middle: sector-wise, the request is:
 # backing: 128m... | -- --
 # active:  128m... | -- 00 00 --
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $((size + 512)) 1024" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -362,7 +362,7 @@
 # Write entire cluster: sector-wise, the request is:
 # backing: 128m... | -- --
 # active:  128m... | 00 00 00 00
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -373,7 +373,7 @@
 # Write at the front: sector-wise, the request is:
 # backing: 128m... | 00 00
 # active:  128m... | 00 -- -- --
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $size 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -381,7 +381,7 @@
 # Write at the back: sector-wise, the request is:
 # backing: 128m... | 00 00
 # active:  128m... | -- -- -- 00
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $((size + 1536)) 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -389,7 +389,7 @@
 # Write at middle: sector-wise, the request is:
 # backing: 128m... | 00 00
 # active:  128m... | -- 00 00 --
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $((size + 512)) 1024" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -397,7 +397,7 @@
 # Write entire cluster: sector-wise, the request is:
 # backing: 128m... | 00 00
 # active:  128m... | 00 00 00 00
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -z $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
@@ -427,7 +427,7 @@
 # Backing file: 128m... | XX --
 # Active layer: 128m... | -- -- 00 --
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $((size + 1024))
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -P 1 $((size)) 512" "$TEST_IMG.base" | _filter_qemu_io
 $QEMU_IO -c "write -z $((size + 1024)) 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "read -P 1 $((size)) 512" "$TEST_IMG" | _filter_qemu_io
@@ -438,7 +438,7 @@
 # Backing file: 128m: ... | -- XX
 # Active layer: 128m: ... | 00 -- -- 00
 CLUSTER_SIZE=512 TEST_IMG="$TEST_IMG.base" _make_test_img $((size + 1024))
-_make_test_img -b "$TEST_IMG.base" $((size + 2048))
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $((size + 2048))
 $QEMU_IO -c "write -P 1 $((size + 512)) 512" "$TEST_IMG.base" | _filter_qemu_io
 $QEMU_IO -c "write -z $((size)) 512" "$TEST_IMG" | _filter_qemu_io
 $QEMU_IO -c "read -P 0 $((size)) 512" "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/154.out b/tests/qemu-iotests/154.out
index fa36733..4863e24 100644
--- a/tests/qemu-iotests/154.out
+++ b/tests/qemu-iotests/154.out
@@ -2,7 +2,7 @@
 
 == backing file contains zeros ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 0
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 10240
@@ -22,7 +22,7 @@
 
 == backing file contains non-zero data before write_zeroes ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 32768
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 1024/1024 bytes at offset 34816
@@ -49,7 +49,7 @@
 
 == backing file contains non-zero data after write_zeroes ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 34816
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 1024/1024 bytes at offset 33792
@@ -76,7 +76,7 @@
 
 == write_zeroes covers non-zero data ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 5120
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 5120
@@ -113,7 +113,7 @@
 
 == spanning two clusters, non-zero before request ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 32768
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 35840
@@ -155,7 +155,7 @@
 
 == spanning two clusters, non-zero after request ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 37888
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 35840
@@ -197,7 +197,7 @@
 
 == spanning two clusters, partially overwriting backing file ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 4096/4096 bytes at offset 2048
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 3072
@@ -217,7 +217,7 @@
 
 == spanning multiple clusters, non-zero in first cluster ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 65536
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 7168/7168 bytes at offset 67584
@@ -233,7 +233,7 @@
 
 == spanning multiple clusters, non-zero in intermediate cluster ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 70656
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 7168/7168 bytes at offset 67584
@@ -246,7 +246,7 @@
 
 == spanning multiple clusters, non-zero in final cluster ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 75776
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 7168/7168 bytes at offset 67584
@@ -262,7 +262,7 @@
 
 == spanning multiple clusters, partially overwriting backing file ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 10240/10240 bytes at offset 66560
 10 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 7168/7168 bytes at offset 67584
@@ -305,25 +305,25 @@
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134219776, "depth": 0, "zero": true, "data": false}]
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134218752
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134217728
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134219264
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 134218240
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 134217728
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
@@ -331,25 +331,25 @@
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
 wrote 512/512 bytes at offset 134217728
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134217728
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134219264
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 1024/1024 bytes at offset 134218240
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2048/2048 bytes at offset 134217728
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
@@ -377,7 +377,7 @@
 
 == unaligned image tail cluster, allocation required ==
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134218752
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134217728
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 512/512 bytes at offset 134218752
@@ -389,7 +389,7 @@
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
 { "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134218752
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 512/512 bytes at offset 134218240
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 512/512 bytes at offset 134217728
diff --git a/tests/qemu-iotests/155 b/tests/qemu-iotests/155
index cb371d4..988f986 100755
--- a/tests/qemu-iotests/155
+++ b/tests/qemu-iotests/155
@@ -60,9 +60,12 @@
 
     def setUp(self):
         qemu_img('create', '-f', iotests.imgfmt, back0_img, '1440K')
-        qemu_img('create', '-f', iotests.imgfmt, '-b', back0_img, back1_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-b', back1_img, back2_img)
-        qemu_img('create', '-f', iotests.imgfmt, '-b', back2_img, source_img)
+        qemu_img('create', '-f', iotests.imgfmt, '-b', back0_img,
+                 '-F', iotests.imgfmt, back1_img)
+        qemu_img('create', '-f', iotests.imgfmt, '-b', back1_img,
+                 '-F', iotests.imgfmt, back2_img)
+        qemu_img('create', '-f', iotests.imgfmt, '-b', back2_img,
+                 '-F', iotests.imgfmt, source_img)
 
         self.vm = iotests.VM()
         # Add the BDS via blockdev-add so it stays around after the mirror block
@@ -89,7 +92,8 @@
         if self.existing:
             if self.target_backing:
                 qemu_img('create', '-f', iotests.imgfmt,
-                         '-b', self.target_backing, target_img, '1440K')
+                         '-b', self.target_backing, '-F', 'raw',
+                         target_img, '1440K')
             else:
                 qemu_img('create', '-f', iotests.imgfmt, target_img, '1440K')
 
diff --git a/tests/qemu-iotests/156 b/tests/qemu-iotests/156
index 5559df6..7c69a6c 100755
--- a/tests/qemu-iotests/156
+++ b/tests/qemu-iotests/156
@@ -56,7 +56,7 @@
 
 # Create source disk
 TEST_IMG="$TEST_IMG.backing" _make_test_img 1M
-_make_test_img -b "$TEST_IMG.backing" 1M
+_make_test_img -b "$TEST_IMG.backing" -F $IMGFMT 1M
 
 $QEMU_IO -c 'write -P 1 0 256k' "$TEST_IMG.backing" | _filter_qemu_io
 $QEMU_IO -c 'write -P 2 64k 192k' "$TEST_IMG" | _filter_qemu_io
@@ -68,7 +68,7 @@
     'return'
 
 # Create snapshot
-TEST_IMG="$TEST_IMG.overlay" _make_test_img -u -b "$TEST_IMG" 1M
+TEST_IMG="$TEST_IMG.overlay" _make_test_img -u -b "$TEST_IMG" -F $IMGFMT 1M
 _send_qemu_cmd $QEMU_HANDLE \
     "{ 'execute': 'blockdev-snapshot-sync',
        'arguments': { 'device': 'source',
@@ -85,7 +85,8 @@
     'return'
 
 # Create target image
-TEST_IMG="$TEST_IMG.target.overlay" _make_test_img -u -b "$TEST_IMG.target" 1M
+TEST_IMG="$TEST_IMG.target.overlay" _make_test_img -u -b "$TEST_IMG.target" \
+    -F $IMGFMT 1M
 
 # Mirror snapshot
 _send_qemu_cmd $QEMU_HANDLE \
@@ -111,7 +112,7 @@
 # Copy source backing chain to the target before completing the job
 cp "$TEST_IMG.backing" "$TEST_IMG.target.backing"
 cp "$TEST_IMG" "$TEST_IMG.target"
-$QEMU_IMG rebase -u -b "$TEST_IMG.target.backing" "$TEST_IMG.target"
+$QEMU_IMG rebase -u -b "$TEST_IMG.target.backing" -F $IMGFMT "$TEST_IMG.target"
 
 # Complete block job
 _send_qemu_cmd $QEMU_HANDLE \
diff --git a/tests/qemu-iotests/156.out b/tests/qemu-iotests/156.out
index 084be5a..cce167b 100644
--- a/tests/qemu-iotests/156.out
+++ b/tests/qemu-iotests/156.out
@@ -1,20 +1,20 @@
 QA output created by 156
 Formatting 'TEST_DIR/t.IMGFMT.backing', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.backing
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.backing backing_fmt=IMGFMT
 wrote 262144/262144 bytes at offset 0
 256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 196608/196608 bytes at offset 65536
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 { 'execute': 'qmp_capabilities' }
 {"return": {}}
-Formatting 'TEST_DIR/t.IMGFMT.overlay', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.overlay', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
 { 'execute': 'blockdev-snapshot-sync', 'arguments': { 'device': 'source', 'snapshot-file': 'TEST_DIR/t.IMGFMT.overlay', 'format': 'IMGFMT', 'mode': 'existing' } }
 {"return": {}}
 { 'execute': 'human-monitor-command', 'arguments': { 'command-line': 'qemu-io source "write -P 3 128k 128k"' } }
 wrote 131072/131072 bytes at offset 131072
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 {"return": ""}
-Formatting 'TEST_DIR/t.IMGFMT.target.overlay', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.target
+Formatting 'TEST_DIR/t.IMGFMT.target.overlay', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.target backing_fmt=IMGFMT
 { 'execute': 'drive-mirror', 'arguments': { 'device': 'source', 'target': 'TEST_DIR/t.IMGFMT.target.overlay', 'mode': 'existing', 'sync': 'top' } }
 {"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "created", "id": "source"}}
 {"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "source"}}
diff --git a/tests/qemu-iotests/158 b/tests/qemu-iotests/158
index ba4db61..3175968 100755
--- a/tests/qemu-iotests/158
+++ b/tests/qemu-iotests/158
@@ -64,7 +64,7 @@
 $QEMU_IO --object $SECRET -c "read -P 0xa 0 $size" --image-opts $IMGSPECBASE | _filter_qemu_io | _filter_testdir
 
 echo "== create overlay =="
-_make_test_img -u --object $SECRET -o "encryption=on,encrypt.key-secret=sec0" -b "$TEST_IMG_BASE" $size
+_make_test_img -u --object $SECRET -o "encryption=on,encrypt.key-secret=sec0" -b "$TEST_IMG_BASE" -F $IMGFMT $size
 
 echo
 echo "== writing part of a cluster =="
diff --git a/tests/qemu-iotests/158.out b/tests/qemu-iotests/158.out
index f28a176..83f1969 100644
--- a/tests/qemu-iotests/158.out
+++ b/tests/qemu-iotests/158.out
@@ -10,7 +10,7 @@
 read 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 == create overlay ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base encryption=on
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT encryption=on
 
 == writing part of a cluster ==
 wrote 1024/1024 bytes at offset 0
diff --git a/tests/qemu-iotests/161 b/tests/qemu-iotests/161
index f572a19..e270976 100755
--- a/tests/qemu-iotests/161
+++ b/tests/qemu-iotests/161
@@ -49,8 +49,8 @@
 
 # Create the images
 TEST_IMG="$TEST_IMG.base" _make_test_img $IMG_SIZE | _filter_imgfmt
-TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" | _filter_imgfmt
-_make_test_img -b "$TEST_IMG.int" | _filter_imgfmt
+TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT | _filter_imgfmt
+_make_test_img -b "$TEST_IMG.int" -F $IMGFMT -F $IMGFMT | _filter_imgfmt
 
 # First test: reopen $TEST.IMG changing the detect-zeroes option on
 # its backing file ($TEST_IMG.int).
@@ -106,8 +106,8 @@
 echo
 # Create the images again
 TEST_IMG="$TEST_IMG.base" _make_test_img $IMG_SIZE | _filter_imgfmt
-TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" | _filter_imgfmt
-_make_test_img -b "$TEST_IMG.int" | _filter_imgfmt
+TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT| _filter_imgfmt
+_make_test_img -b "$TEST_IMG.int" -F $IMGFMT | _filter_imgfmt
 
 _launch_qemu -drive if=none,file="${TEST_IMG}"
 _send_qemu_cmd $QEMU_HANDLE \
diff --git a/tests/qemu-iotests/161.out b/tests/qemu-iotests/161.out
index aef9741..3d8d89a 100644
--- a/tests/qemu-iotests/161.out
+++ b/tests/qemu-iotests/161.out
@@ -1,7 +1,7 @@
 QA output created by 161
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int
+Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int backing_fmt=IMGFMT
 
 *** Change an option on the backing file
 
@@ -29,8 +29,8 @@
 *** Commit and then change an option on the backing file
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int
+Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int backing_fmt=IMGFMT
 { 'execute': 'qmp_capabilities' }
 {"return": {}}
 { 'execute': 'block-commit', 'arguments': { 'device': 'none0', 'top': 'TEST_DIR/t.IMGFMT.int' } }
diff --git a/tests/qemu-iotests/176 b/tests/qemu-iotests/176
index 117c8b6..2565ff1 100755
--- a/tests/qemu-iotests/176
+++ b/tests/qemu-iotests/176
@@ -84,8 +84,8 @@
 
 len=$((2100 * 1024 * 1024 + 512)) # larger than 2G, and not cluster aligned
 TEST_IMG="$TEST_IMG.base" _make_test_img $len
-TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" $len
-_make_test_img -b "$TEST_IMG.itmd" $len
+TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT $len
+_make_test_img -b "$TEST_IMG.itmd" -F $IMGFMT $len
 # Update the top image to use a feature that is incompatible with fast path
 case $reason in
     snapshot) $QEMU_IMG snapshot -c snap "$TEST_IMG" ;;
diff --git a/tests/qemu-iotests/176.out b/tests/qemu-iotests/176.out
index cc33def..9d09b60 100644
--- a/tests/qemu-iotests/176.out
+++ b/tests/qemu-iotests/176.out
@@ -3,8 +3,8 @@
 === Test pass snapshot.0 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -43,8 +43,8 @@
 === Test pass snapshot.1 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -84,8 +84,8 @@
 === Test pass snapshot.2 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -125,8 +125,8 @@
 === Test pass snapshot.3 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 wrote 196608/196608 bytes at offset 2147287040
 192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 131072/131072 bytes at offset 2147352576
@@ -163,8 +163,8 @@
 === Test pass bitmap.0 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 QMP_VERSION
 {"return": {}}
 {"return": {}}
@@ -212,8 +212,8 @@
 === Test pass bitmap.1 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 QMP_VERSION
 {"return": {}}
 {"return": {}}
@@ -262,8 +262,8 @@
 === Test pass bitmap.2 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 QMP_VERSION
 {"return": {}}
 {"return": {}}
@@ -312,8 +312,8 @@
 === Test pass bitmap.3 ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=2202010112
-Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd
+Formatting 'TEST_DIR/t.IMGFMT.itmd', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2202010112 backing_file=TEST_DIR/t.IMGFMT.itmd backing_fmt=IMGFMT
 QMP_VERSION
 {"return": {}}
 {"return": {}}
diff --git a/tests/qemu-iotests/177 b/tests/qemu-iotests/177
index eadc2c7..5d4a77a 100755
--- a/tests/qemu-iotests/177
+++ b/tests/qemu-iotests/177
@@ -51,7 +51,7 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img $size
 $QEMU_IO -c "write -P 11 0 $size" "$TEST_IMG.base" | _filter_qemu_io
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 $QEMU_IO -c "write -P 22 0 $size" "$TEST_IMG" | _filter_qemu_io
 
 # Limited to 64k max-transfer
diff --git a/tests/qemu-iotests/177.out b/tests/qemu-iotests/177.out
index e887542..ba1e1e2 100644
--- a/tests/qemu-iotests/177.out
+++ b/tests/qemu-iotests/177.out
@@ -4,7 +4,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
 wrote 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
diff --git a/tests/qemu-iotests/179 b/tests/qemu-iotests/179
index 9372dc3..11a20cb 100755
--- a/tests/qemu-iotests/179
+++ b/tests/qemu-iotests/179
@@ -49,7 +49,7 @@
 echo
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 # Offsets chosen at or near 2M boundaries so test works at all cluster sizes
 # 8k and larger (smaller clusters fail due to non-contiguous allocations)
diff --git a/tests/qemu-iotests/179.out b/tests/qemu-iotests/179.out
index 80722b2..1f76800 100644
--- a/tests/qemu-iotests/179.out
+++ b/tests/qemu-iotests/179.out
@@ -3,7 +3,7 @@
 === Testing write zeroes with unmap ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 2097152/2097152 bytes at offset 2097152
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2097152/2097152 bytes at offset 6291456
diff --git a/tests/qemu-iotests/189 b/tests/qemu-iotests/189
index e6a84b8..3e5ded1 100755
--- a/tests/qemu-iotests/189
+++ b/tests/qemu-iotests/189
@@ -66,7 +66,7 @@
 $QEMU_IO --object $SECRET0 -c "read -P 0xa 0 $size" --image-opts $IMGSPECBASE | _filter_qemu_io | _filter_testdir
 
 echo "== create overlay =="
-_make_test_img --object $SECRET1 -o "encrypt.format=luks,encrypt.key-secret=sec1,encrypt.iter-time=10" -u -b "$TEST_IMG_BASE" $size
+_make_test_img --object $SECRET1 -o "encrypt.format=luks,encrypt.key-secret=sec1,encrypt.iter-time=10" -u -b "$TEST_IMG_BASE" -F $IMGFMT $size
 
 echo
 echo "== writing part of a cluster =="
diff --git a/tests/qemu-iotests/189.out b/tests/qemu-iotests/189.out
index bc213cb..30af0a8 100644
--- a/tests/qemu-iotests/189.out
+++ b/tests/qemu-iotests/189.out
@@ -10,7 +10,7 @@
 read 16777216/16777216 bytes at offset 0
 16 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 == create overlay ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == writing part of a cluster ==
 wrote 1024/1024 bytes at offset 0
diff --git a/tests/qemu-iotests/191 b/tests/qemu-iotests/191
index b05db68..d17462e 100755
--- a/tests/qemu-iotests/191
+++ b/tests/qemu-iotests/191
@@ -54,8 +54,8 @@
 
 TEST_IMG="${TEST_IMG}.base" _make_test_img $size
 TEST_IMG="${TEST_IMG}.mid" _make_test_img -o "backing_fmt=$IMGFMT" -b "${TEST_IMG}.base"
-_make_test_img -b "${TEST_IMG}.mid"
-TEST_IMG="${TEST_IMG}.ovl2" _make_test_img -b "${TEST_IMG}.mid"
+_make_test_img -b "${TEST_IMG}.mid" -F $IMGFMT
+TEST_IMG="${TEST_IMG}.ovl2" _make_test_img -b "${TEST_IMG}.mid" -F $IMGFMT
 
 $QEMU_IO -c 'write -P 0x55 1M 64k' "${TEST_IMG}.mid" | _filter_qemu_io
 
@@ -102,10 +102,10 @@
 echo
 
 TEST_IMG="${TEST_IMG}.base" _make_test_img $size
-TEST_IMG="${TEST_IMG}.mid" _make_test_img -b "${TEST_IMG}.base"
-_make_test_img -b "${TEST_IMG}.mid"
-TEST_IMG="${TEST_IMG}.ovl2" _make_test_img -b "${TEST_IMG}.mid"
-TEST_IMG="${TEST_IMG}.ovl3" _make_test_img -b "${TEST_IMG}.ovl2"
+TEST_IMG="${TEST_IMG}.mid" _make_test_img -b "${TEST_IMG}.base" -F $IMGFMT
+_make_test_img -b "${TEST_IMG}.mid" -F $IMGFMT
+TEST_IMG="${TEST_IMG}.ovl2" _make_test_img -b "${TEST_IMG}.mid" -F $IMGFMT
+TEST_IMG="${TEST_IMG}.ovl3" _make_test_img -b "${TEST_IMG}.ovl2" -F $IMGFMT
 
 $QEMU_IO -c 'write -P 0x55 1M 64k' "${TEST_IMG}.mid" | _filter_qemu_io
 
diff --git a/tests/qemu-iotests/191.out b/tests/qemu-iotests/191.out
index 34cec7b..11aaf3b 100644
--- a/tests/qemu-iotests/191.out
+++ b/tests/qemu-iotests/191.out
@@ -4,8 +4,8 @@
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
 Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
-Formatting 'TEST_DIR/t.IMGFMT.ovl2', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.ovl2', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 1048576
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 { 'execute': 'qmp_capabilities' }
@@ -413,10 +413,10 @@
 === Preparing and starting VM with -drive ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
-Formatting 'TEST_DIR/t.IMGFMT.ovl2', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
-Formatting 'TEST_DIR/t.IMGFMT.ovl3', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.ovl2
+Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.ovl2', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT.ovl3', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.ovl2 backing_fmt=IMGFMT
 wrote 65536/65536 bytes at offset 1048576
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 { 'execute': 'qmp_capabilities' }
diff --git a/tests/qemu-iotests/195 b/tests/qemu-iotests/195
index 48984b7..2351d55 100755
--- a/tests/qemu-iotests/195
+++ b/tests/qemu-iotests/195
@@ -56,8 +56,8 @@
 
 size=64M
 TEST_IMG="$TEST_IMG.base" _make_test_img $size
-TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
-_make_test_img -b "$TEST_IMG.mid"
+TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT
+_make_test_img -b "$TEST_IMG.mid" -F $IMGFMT
 
 echo
 echo "Change backing file of mid (opened read-only)"
@@ -75,7 +75,7 @@
 echo "Change backing file of top (opened writable)"
 echo
 
-TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
+TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 run_qemu -drive if=none,file="$TEST_IMG",node-name=top <<EOF
 {"execute":"qmp_capabilities"}
diff --git a/tests/qemu-iotests/195.out b/tests/qemu-iotests/195.out
index e6df0d6..ec84df5 100644
--- a/tests/qemu-iotests/195.out
+++ b/tests/qemu-iotests/195.out
@@ -1,7 +1,7 @@
 QA output created by 195
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
+Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
 
 Change backing file of mid (opened read-only)
 
@@ -42,7 +42,7 @@
 
 Change backing file of top (opened writable)
 
-Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Testing: -drive if=none,file=TEST_DIR/t.IMGFMT,node-name=top
 {
     QMP_VERSION
diff --git a/tests/qemu-iotests/198 b/tests/qemu-iotests/198
index aeb059d..1b9bfb8 100755
--- a/tests/qemu-iotests/198
+++ b/tests/qemu-iotests/198
@@ -63,7 +63,7 @@
 $QEMU_IO --object $SECRET0 -c "write -P 0xa 0 $size" --image-opts $IMGSPECBASE | _filter_qemu_io | _filter_testdir
 
 echo "== create overlay =="
-_make_test_img --object $SECRET1 -o "encrypt.format=luks,encrypt.key-secret=sec1,encrypt.iter-time=10" -u -b "$TEST_IMG_BASE" $size
+_make_test_img --object $SECRET1 -o "encrypt.format=luks,encrypt.key-secret=sec1,encrypt.iter-time=10" -u -b "$TEST_IMG_BASE" -F $IMGFMT $size
 
 echo
 echo "== writing whole image layer =="
diff --git a/tests/qemu-iotests/198.out b/tests/qemu-iotests/198.out
index 4b800e7..3952708 100644
--- a/tests/qemu-iotests/198.out
+++ b/tests/qemu-iotests/198.out
@@ -6,7 +6,7 @@
 wrote 16777216/16777216 bytes at offset 0
 16 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 == create overlay ==
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=16777216 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 == writing whole image layer ==
 wrote 16777216/16777216 bytes at offset 0
@@ -79,6 +79,7 @@
 file format: IMGFMT
 virtual size: 16 MiB (16777216 bytes)
 backing file: TEST_DIR/t.IMGFMT.base
+backing file format: IMGFMT
 Format specific information:
     compression type: zlib
     encrypt:
diff --git a/tests/qemu-iotests/204 b/tests/qemu-iotests/204
index abb73dc..6770fa9 100755
--- a/tests/qemu-iotests/204
+++ b/tests/qemu-iotests/204
@@ -52,7 +52,7 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img $size
 $QEMU_IO -c "write -P 11 0 $size" "$TEST_IMG.base" | _filter_qemu_io
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 $QEMU_IO -c "write -P 22 0 110M" "$TEST_IMG" | _filter_qemu_io
 
 # Limited to 64k max-transfer
diff --git a/tests/qemu-iotests/204.out b/tests/qemu-iotests/204.out
index f3a10fb..457f72d 100644
--- a/tests/qemu-iotests/204.out
+++ b/tests/qemu-iotests/204.out
@@ -4,7 +4,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
 wrote 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 wrote 115343360/115343360 bytes at offset 0
 110 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
diff --git a/tests/qemu-iotests/216 b/tests/qemu-iotests/216
index de11d85..f93c61a 100755
--- a/tests/qemu-iotests/216
+++ b/tests/qemu-iotests/216
@@ -53,7 +53,7 @@
     assert qemu_img('create', '-f', iotests.imgfmt, base_img_path, '64M') == 0
     assert qemu_io_silent(base_img_path, '-c', 'write -P 1 0M 1M') == 0
     assert qemu_img('create', '-f', iotests.imgfmt, '-b', base_img_path,
-                    top_img_path) == 0
+                    '-F', iotests.imgfmt, top_img_path) == 0
     assert qemu_io_silent(top_img_path,  '-c', 'write -P 2 1M 1M') == 0
 
     log('Done')
diff --git a/tests/qemu-iotests/224 b/tests/qemu-iotests/224
index 81ca1e4..017b068 100755
--- a/tests/qemu-iotests/224
+++ b/tests/qemu-iotests/224
@@ -49,9 +49,9 @@
         assert qemu_img('create', '-f', iotests.imgfmt,
                         base_img_path, '64M') == 0
         assert qemu_img('create', '-f', iotests.imgfmt, '-b', base_img_path,
-                        mid_img_path) == 0
+                        '-F', iotests.imgfmt, mid_img_path) == 0
         assert qemu_img('create', '-f', iotests.imgfmt, '-b', mid_img_path,
-                        top_img_path) == 0
+                        '-F', iotests.imgfmt, top_img_path) == 0
 
         # Something to commit
         assert qemu_io_silent(mid_img_path, '-c', 'write -P 1 0 1M') == 0
diff --git a/tests/qemu-iotests/225 b/tests/qemu-iotests/225
index c9a334c..0186ec8 100755
--- a/tests/qemu-iotests/225
+++ b/tests/qemu-iotests/225
@@ -48,7 +48,7 @@
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 1M
 TEST_IMG="$TEST_IMG.not_base" _make_test_img 1M
-_make_test_img -b "$TEST_IMG.base"
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT
 
 make_opts()
 {
diff --git a/tests/qemu-iotests/225.out b/tests/qemu-iotests/225.out
index 4dc8ee2..0998ae0 100644
--- a/tests/qemu-iotests/225.out
+++ b/tests/qemu-iotests/225.out
@@ -1,7 +1,7 @@
 QA output created by 225
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
 Formatting 'TEST_DIR/t.IMGFMT.not_base', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 
 === Testing fitting VMDK backing image ===
 
diff --git a/tests/qemu-iotests/228 b/tests/qemu-iotests/228
index da0900f..60db986 100755
--- a/tests/qemu-iotests/228
+++ b/tests/qemu-iotests/228
@@ -56,7 +56,8 @@
     assert qemu_img('create', '-f', iotests.imgfmt, base_img_path, '64M') == 0
     # Choose a funny way to describe the backing filename
     assert qemu_img('create', '-f', iotests.imgfmt, '-b',
-                    'file:' + base_img_path, top_img_path) == 0
+                    'file:' + base_img_path, '-F', iotests.imgfmt,
+                    top_img_path) == 0
 
     vm.launch()
 
@@ -171,7 +172,7 @@
     # filename unless the backing file is opened implicitly with the
     # overlay)
     assert qemu_img('create', '-f', iotests.imgfmt, '-b', base_img_path,
-                    top_img_path) == 0
+                    '-F', iotests.imgfmt, top_img_path) == 0
 
     # You can only reliably override backing options by using a node
     # reference (or by specifying file.filename, but, well...)
diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
index 4f5f0bb..ad91a6f 100755
--- a/tests/qemu-iotests/245
+++ b/tests/qemu-iotests/245
@@ -44,7 +44,8 @@
 
     def setUp(self):
         qemu_img('create', '-f', iotests.imgfmt, hd_path[0], '3M')
-        qemu_img('create', '-f', iotests.imgfmt, '-b', hd_path[0], hd_path[1])
+        qemu_img('create', '-f', iotests.imgfmt, '-b', hd_path[0],
+                 '-F', iotests.imgfmt, hd_path[1])
         qemu_img('create', '-f', iotests.imgfmt, hd_path[2], '3M')
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xa0  0 1M', hd_path[0])
         qemu_io('-f', iotests.imgfmt, '-c', 'write -P 0xa1 1M 1M', hd_path[1])
diff --git a/tests/qemu-iotests/249 b/tests/qemu-iotests/249
index 2b99c97..68f13ed 100755
--- a/tests/qemu-iotests/249
+++ b/tests/qemu-iotests/249
@@ -49,8 +49,8 @@
 
 # Create the images: base <- int <- active
 TEST_IMG="$TEST_IMG.base" _make_test_img $IMG_SIZE | _filter_imgfmt
-TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" | _filter_imgfmt
-_make_test_img -b "$TEST_IMG.int" | _filter_imgfmt
+TEST_IMG="$TEST_IMG.int" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT | _filter_imgfmt
+_make_test_img -b "$TEST_IMG.int" -F $IMGFMT | _filter_imgfmt
 
 # Launch QEMU with these two drives:
 # none0: base (read-only)
diff --git a/tests/qemu-iotests/249.out b/tests/qemu-iotests/249.out
index 51307ed..85acda4 100644
--- a/tests/qemu-iotests/249.out
+++ b/tests/qemu-iotests/249.out
@@ -1,7 +1,7 @@
 QA output created by 249
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1048576
-Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int
+Formatting 'TEST_DIR/t.IMGFMT.int', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=TEST_DIR/t.IMGFMT.int backing_fmt=IMGFMT
 { 'execute': 'qmp_capabilities' }
 {"return": {}}
 
diff --git a/tests/qemu-iotests/252 b/tests/qemu-iotests/252
index 83280c1..6662f4c 100755
--- a/tests/qemu-iotests/252
+++ b/tests/qemu-iotests/252
@@ -101,7 +101,7 @@
 
 echo
 
-$QEMU_IMG rebase -b "$TEST_IMG.base_new" "$TEST_IMG"
+$QEMU_IMG rebase -b "$TEST_IMG.base_new" -F $IMGFMT "$TEST_IMG"
 
 # Verify the data is correct
 $QEMU_IO "$TEST_IMG" \
diff --git a/tests/qemu-iotests/257 b/tests/qemu-iotests/257
index 004a433..e1e6077 100755
--- a/tests/qemu-iotests/257
+++ b/tests/qemu-iotests/257
@@ -238,7 +238,8 @@
     """
     expected_ret = 0 if expected_match else 1
     if baseimg:
-        assert qemu_img("rebase", "-u", "-b", baseimg, image) == 0
+        assert qemu_img("rebase", "-u", "-b", baseimg, '-F', iotests.imgfmt,
+                        image) == 0
     ret = qemu_img("compare", image, reference)
     log('qemu_img compare "{:s}" "{:s}" ==> {:s}, {:s}'.format(
         image, reference,
diff --git a/tests/qemu-iotests/267 b/tests/qemu-iotests/267
index 3146273..e44be49 100755
--- a/tests/qemu-iotests/267
+++ b/tests/qemu-iotests/267
@@ -73,7 +73,7 @@
 run_test()
 {
     if [ -n "$BACKING_FILE" ]; then
-        _make_test_img -b "$BACKING_FILE" $size
+        _make_test_img -b "$BACKING_FILE" -F $IMGFMT $size
     else
         _make_test_img $size
     fi
@@ -149,7 +149,7 @@
 echo "=== -blockdev with NBD server on the backing file ==="
 echo
 
-_make_test_img -b "$TEST_IMG.base" $size
+_make_test_img -b "$TEST_IMG.base" -F $IMGFMT $size
 cat <<EOF |
 nbd_server_start unix:$SOCK_DIR/nbd
 nbd_server_add -w backing-fmt
diff --git a/tests/qemu-iotests/267.out b/tests/qemu-iotests/267.out
index 8dddb4b..d6d80c0 100644
--- a/tests/qemu-iotests/267.out
+++ b/tests/qemu-iotests/267.out
@@ -128,7 +128,7 @@
 === -blockdev with a backing file ===
 
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT.base,node-name=backing-file -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,backing=backing-file,node-name=fmt
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
@@ -139,7 +139,7 @@
 (qemu) loadvm snap0
 (qemu) quit
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT.base,node-name=backing-file -blockdev driver=IMGFMT,file=backing-file,node-name=backing-fmt -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,backing=backing-fmt,node-name=fmt
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) savevm snap0
@@ -158,7 +158,7 @@
 
 === -blockdev with NBD server on the backing file ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT.base,node-name=backing-file -blockdev driver=IMGFMT,file=backing-file,node-name=backing-fmt -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,backing=backing-fmt,node-name=fmt
 QEMU X.Y.Z monitor - type 'help' for more information
 (qemu) nbd_server_start unix:SOCK_DIR/nbd
diff --git a/tests/qemu-iotests/270 b/tests/qemu-iotests/270
index b9a12b9..00339c0 100755
--- a/tests/qemu-iotests/270
+++ b/tests/qemu-iotests/270
@@ -53,7 +53,7 @@
 # We need a large cluster size, see below for why (above the $QEMU_IO
 # invocation)
 _make_test_img -o cluster_size=2M,data_file="$TEST_IMG.orig" \
-    -b "$TEST_IMG.base" 4G
+    -b "$TEST_IMG.base" -F $IMGFMT 4G
 
 # We want a null-co as the data file, because it allows us to quickly
 # "write" 2G of data without using any space.
diff --git a/tests/qemu-iotests/270.out b/tests/qemu-iotests/270.out
index c7be111..6dc3b23 100644
--- a/tests/qemu-iotests/270.out
+++ b/tests/qemu-iotests/270.out
@@ -2,7 +2,7 @@
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=4294967296
 wrote 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294967296 backing_file=TEST_DIR/t.IMGFMT.base data_file=TEST_DIR/t.IMGFMT.orig
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294967296 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT data_file=TEST_DIR/t.IMGFMT.orig
 wrote 2147483136/2147483136 bytes at offset 768
 2 GiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 No errors were found on the image.
diff --git a/tests/qemu-iotests/273 b/tests/qemu-iotests/273
index 00ff79b..41ffbf3 100755
--- a/tests/qemu-iotests/273
+++ b/tests/qemu-iotests/273
@@ -56,8 +56,8 @@
 }
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
-_make_test_img -b "$TEST_IMG.mid"
+TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT
+_make_test_img -b "$TEST_IMG.mid" -F $IMGFMT
 
 run_qemu \
     -blockdev file,node-name=base,filename="$TEST_IMG.base" \
diff --git a/tests/qemu-iotests/273.out b/tests/qemu-iotests/273.out
index 684b8d6..87d4758 100644
--- a/tests/qemu-iotests/273.out
+++ b/tests/qemu-iotests/273.out
@@ -1,7 +1,7 @@
 QA output created by 273
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
+Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
 Testing: -blockdev file,node-name=base,filename=TEST_DIR/t.IMGFMT.base -blockdev file,node-name=midf,filename=TEST_DIR/t.IMGFMT.mid -blockdev {"driver":"IMGFMT","node-name":"mid","file":"midf","backing":null} -blockdev file,node-name=topf,filename=TEST_DIR/t.IMGFMT -blockdev {"driver":"IMGFMT","file":"topf","node-name":"top","backing":null}
 {
     QMP_VERSION
diff --git a/tests/qemu-iotests/274 b/tests/qemu-iotests/274
index 5d1bf34..d4571c5 100755
--- a/tests/qemu-iotests/274
+++ b/tests/qemu-iotests/274
@@ -31,10 +31,10 @@
 def create_chain() -> None:
     iotests.qemu_img_log('create', '-f', iotests.imgfmt, base,
                          str(size_long))
-    iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', base, mid,
-                         str(size_short))
-    iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', mid, top,
-                         str(size_long))
+    iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', base,
+                         '-F', iotests.imgfmt, mid, str(size_short))
+    iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', mid,
+                         '-F', iotests.imgfmt, top, str(size_long))
 
     iotests.qemu_io_log('-c', 'write -P 1 0 %d' % size_long, base)
 
@@ -139,8 +139,8 @@
 
         iotests.log('=== preallocation=%s ===' % prealloc)
         iotests.qemu_img_log('create', '-f', iotests.imgfmt, base, base_size)
-        iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', base, top,
-                             top_size_old)
+        iotests.qemu_img_log('create', '-f', iotests.imgfmt, '-b', base,
+                             '-F', iotests.imgfmt, top, top_size_old)
         iotests.qemu_io_log('-c', 'write -P 1 %s 64k' % off, base)
 
         # After this, top_size_old to base_size should be allocated/zeroed.
diff --git a/tests/qemu-iotests/274.out b/tests/qemu-iotests/274.out
index d248a1e..3a36fe7 100644
--- a/tests/qemu-iotests/274.out
+++ b/tests/qemu-iotests/274.out
@@ -1,9 +1,9 @@
 == Commit tests ==
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 2097152/2097152 bytes at offset 0
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -50,6 +50,7 @@
 virtual size: 2 MiB (2097152 bytes)
 cluster_size: 65536
 backing file: TEST_DIR/PID-base
+backing file format: IMGFMT
 Format specific information:
     compat: 1.1
     compression type: zlib
@@ -66,9 +67,9 @@
 === Testing HMP commit (top -> mid) ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 2097152/2097152 bytes at offset 0
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -80,6 +81,7 @@
 virtual size: 2 MiB (2097152 bytes)
 cluster_size: 65536
 backing file: TEST_DIR/PID-base
+backing file format: IMGFMT
 Format specific information:
     compat: 1.1
     compression type: zlib
@@ -96,9 +98,9 @@
 === Testing QMP active commit (top -> mid) ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-mid', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1048576 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=2097152 backing_file=TEST_DIR/PID-mid backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 2097152/2097152 bytes at offset 0
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -116,6 +118,7 @@
 virtual size: 2 MiB (2097152 bytes)
 cluster_size: 65536
 backing file: TEST_DIR/PID-base
+backing file format: IMGFMT
 Format specific information:
     compat: 1.1
     compression type: zlib
@@ -133,7 +136,7 @@
 === preallocation=off ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=6442450944 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1073741824 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=1073741824 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 5368709120
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -152,7 +155,7 @@
 === preallocation=metadata ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=34359738368 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=32212254720 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=32212254720 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 33285996544
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -176,7 +179,7 @@
 === preallocation=falloc ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=10485760 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=5242880 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=5242880 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 9437184
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -195,7 +198,7 @@
 === preallocation=full ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=16777216 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=8388608 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=8388608 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 11534336
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -214,7 +217,7 @@
 === preallocation=off ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=393216 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=259072 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=259072 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 259072
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -234,7 +237,7 @@
 === preallocation=off ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=409600 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=262144 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=262144 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 344064
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -253,7 +256,7 @@
 === preallocation=off ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 cluster_size=65536 compression_type=zlib size=524288 lazy_refcounts=off refcount_bits=16
 
-Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=262144 backing_file=TEST_DIR/PID-base lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 cluster_size=65536 compression_type=zlib size=262144 backing_file=TEST_DIR/PID-base backing_fmt=qcow2 lazy_refcounts=off refcount_bits=16
 
 wrote 65536/65536 bytes at offset 446464
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
diff --git a/tests/qemu-iotests/279 b/tests/qemu-iotests/279
index 75a4747..5515d4e 100755
--- a/tests/qemu-iotests/279
+++ b/tests/qemu-iotests/279
@@ -42,8 +42,8 @@
                      "subformat=twoGbMaxExtentFlat" \
 
 TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base"
-_make_test_img -b "$TEST_IMG.mid"
+TEST_IMG="$TEST_IMG.mid" _make_test_img -b "$TEST_IMG.base" -F $IMGFMT
+_make_test_img -b "$TEST_IMG.mid" -F $IMGFMT
 
 echo
 echo '== qemu-img info --backing-chain =='
diff --git a/tests/qemu-iotests/279.out b/tests/qemu-iotests/279.out
index f4dc6c6..adb2e47 100644
--- a/tests/qemu-iotests/279.out
+++ b/tests/qemu-iotests/279.out
@@ -1,7 +1,7 @@
 QA output created by 279
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
-Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid
+Formatting 'TEST_DIR/t.IMGFMT.mid', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.mid backing_fmt=IMGFMT
 
 == qemu-img info --backing-chain ==
 image: TEST_DIR/t.IMGFMT
diff --git a/tests/qemu-iotests/290 b/tests/qemu-iotests/290
index 776b65e..01ee14d 100755
--- a/tests/qemu-iotests/290
+++ b/tests/qemu-iotests/290
@@ -71,7 +71,7 @@
 
 for qcow2_compat in 0.10 1.1; do
     echo "# Create an image with compat=$qcow2_compat and a backing file"
-    _make_test_img -o "compat=$qcow2_compat" -b "$BACKING_IMG"
+    _make_test_img -o "compat=$qcow2_compat" -b "$BACKING_IMG" -F $IMGFMT
 
     echo "# Fill all clusters with data and then discard them"
     $QEMU_IO -c 'write -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io
diff --git a/tests/qemu-iotests/290.out b/tests/qemu-iotests/290.out
index d2259c8..22b4765 100644
--- a/tests/qemu-iotests/290.out
+++ b/tests/qemu-iotests/290.out
@@ -34,7 +34,7 @@
 wrote 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 # Create an image with compat=0.10 and a backing file
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 # Fill all clusters with data and then discard them
 wrote 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -47,7 +47,7 @@
 Offset          Length          Mapped to       File
 0               0x20000         0x50000         TEST_DIR/t.qcow2
 # Create an image with compat=1.1 and a backing file
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
 # Fill all clusters with data and then discard them
 wrote 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)