commit 4a0082401a770261b85625a41eef4a4e89ad7a74
author Max Reitz <mreitz@redhat.com> Thu Apr 13 18:06:24 2017 +0200
committer Kevin Wolf <kwolf@redhat.com> Thu Apr 27 15:39:49 2017 +0200
tree c738f8dda6e272107fdedd83d23cc1fd8915c4e6
parent 312758e23724044adb66ad1cd7fcde399817ec5b

block: An empty filename counts as no filename

Reproducer:
    $ ./qemu-img info ''
    qemu-img: ./block.c:1008: bdrv_open_driver: Assertion
        `!drv->bdrv_needs_filename || bs->filename[0]' failed.
    [1]    26105 abort (core dumped)  ./qemu-img info ''

This patch fixes this to be:
    $ ./qemu-img info ''
    qemu-img: Could not open '': The 'file' block driver requires a file
    name

Cc: qemu-stable <qemu-stable@nongnu.org>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

diff --git a/block.c b/block.c
index ceaca44..7b557f3 100644
--- a/block.c
+++ b/block.c
@@ -1204,7 +1204,7 @@
         filename = qdict_get_try_str(options, "filename");
     }
 
-    if (drv->bdrv_needs_filename && !filename) {
+    if (drv->bdrv_needs_filename && (!filename || !filename[0])) {
         error_setg(errp, "The '%s' block driver requires a file name",
                    drv->format_name);
         ret = -EINVAL;