[Qemu-devel] [PATCH v7 4/8] block: Fix dirty bitmap in bdrv_co_discard

[Fam Zheng <famz@redhat.com>]

Unsetting dirty globally with discard is not very correct. The discard may zero
out sectors (depending on can_write_zeroes_with_unmap), we should replicate
this change to destination side to make sure that the guest sees the same data.

Calling bdrv_reset_dirty also troubles mirror job because the hbitmap iterator
doesn't expect unsetting of bits after current position.

So let's do it the opposite way which fixes both problems: set the dirty bits
if we are to discard it.

Reported-by: wangxiaolong@ucloud.cn
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/io.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/io.c b/block/io.c
index 41463a6..a71346c 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2440,8 +2440,6 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
         return -EPERM;
     }
 
-    bdrv_reset_dirty(bs, sector_num, nb_sectors);
-
     /* Do nothing if disabled.  */
     if (!(bs->open_flags & BDRV_O_UNMAP)) {
         return 0;
@@ -2451,6 +2449,8 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
         return 0;
     }
 
+    bdrv_set_dirty(bs, sector_num, nb_sectors);
+
     max_discard = MIN_NON_ZERO(bs->bl.max_discard, BDRV_REQUEST_MAX_SECTORS);
     while (nb_sectors > 0) {
         int ret;
-- 
2.4.2