COW: Extend checking allocated bits to beyond one sector
cow_co_is_allocated() only checks one sector's worth of allocated bits
before returning. This is allowed but (slightly) inefficient, so extend
it to check all of the file's metadata sectors.
Signed-off-by: Charlie Shepherd <charlie@ctshepherd.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
[kwolf: silenced compiler warning (-Wmaybe-uninitialized for changed)]
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block/cow.c b/block/cow.c
index f759496..dc15e46 100644
--- a/block/cow.c
+++ b/block/cow.c
@@ -152,18 +152,34 @@
{
int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
- uint8_t bitmap[BDRV_SECTOR_SIZE];
- int ret;
- int changed;
+ bool first = true;
+ int changed = 0, same = 0;
- ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
- if (ret < 0) {
- return ret;
- }
+ do {
+ int ret;
+ uint8_t bitmap[BDRV_SECTOR_SIZE];
- bitnum &= BITS_PER_BITMAP_SECTOR - 1;
- changed = cow_test_bit(bitnum, bitmap);
- *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
+ bitnum &= BITS_PER_BITMAP_SECTOR - 1;
+ int sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum);
+
+ ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
+ if (ret < 0) {
+ return ret;
+ }
+
+ if (first) {
+ changed = cow_test_bit(bitnum, bitmap);
+ first = false;
+ }
+
+ same += cow_find_streak(bitmap, changed, bitnum, nb_sectors);
+
+ bitnum += sector_bits;
+ nb_sectors -= sector_bits;
+ offset += BDRV_SECTOR_SIZE;
+ } while (nb_sectors);
+
+ *num_same = same;
return changed;
}
