[Qemu-devel] [PATCH 1/1] mirror: fix improperly filled copy_bitmap for mirror block job

["Denis V. Lunev" <den@openvz.org>]

bdrv_is_allocated_above() returns true in the case if qcow2 even for
completely zeroed areas as BDRV_BLOCK_ALLOCATED flag is set in both
cases. Though we have completely zeroed out the image just above or it was
already zeroed.

The patch stops using bdrv_is_allocated_above() wrapper and switches to
bdrv_get_block_status_above() to distinguish zeroed areas and areas with
data to avoid extra IO operations, which could be VERY slow.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Jeff Cody <jcody@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
---
 block/mirror.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index e0b3f41..87edbd8 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -552,7 +552,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
     BlockDriverState *base = s->base;
     BlockDriverState *bs = blk_bs(s->common.blk);
     BlockDriverState *target_bs = blk_bs(s->target);
-    int ret, n;
+    int n;
 
     end = s->bdev_length / BDRV_SECTOR_SIZE;
 
@@ -590,6 +590,8 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
         /* Just to make sure we are not exceeding int limit. */
         int nb_sectors = MIN(INT_MAX >> BDRV_SECTOR_BITS,
                              end - sector_num);
+        int64_t status;
+        BlockDriverState *file;
 
         mirror_throttle(s);
 
@@ -597,13 +599,14 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             return 0;
         }
 
-        ret = bdrv_is_allocated_above(bs, base, sector_num, nb_sectors, &n);
-        if (ret < 0) {
-            return ret;
+        status = bdrv_get_block_status_above(bs, base, sector_num,
+                                             nb_sectors, &n, &file);
+        if (status < 0) {
+            return status;
         }
 
         assert(n > 0);
-        if (ret == 1) {
+        if (status & BDRV_BLOCK_DATA) {
             bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
         }
         sector_num += n;
-- 
2.7.4