[Qemu-devel] [PATCH v3] block: mirror - fix full sync mode when target does not support zero init

[Jeff Cody]

During mirror, if the target device does not support zero init, a
mirror may result in a corrupted image for sync="full" mode.

This is due to how the initial dirty bitmap is set up prior to copying
data - we did not mark sectors as dirty that are unallocated.  This
means those unallocated sectors are skipped over on the target, and for
a device without zero init, invalid data may reside in those holes.

If both of the following conditions are true, then we will explicitly
mark all sectors as dirty:

    1.) sync = "full"
    2.) bdrv_has_zero_init(target) == false

If the target does support zero init, but a target image is passed in
with data already present (i.e. an "existing" image), it is assumed the
data present in the existing image is valid data for those sectors.

Signed-off-by: Jeff Cody <address@hidden>
---
 block/mirror.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index a258926..ce367e0 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -455,6 +455,8 @@ static void coroutine_fn mirror_run(void *opaque)
     if (!s->is_none_mode) {
         /* First part, loop on the sectors and initialize the dirty bitmap.  */
         BlockDriverState *base = s->base;
+        bool mark_all_dirty = s->base == NULL && 
!bdrv_has_zero_init(s->target);
+
         for (sector_num = 0; sector_num < end; ) {
             /* Just to make sure we are not exceeding int limit. */
             int nb_sectors = MIN(INT_MAX >> BDRV_SECTOR_BITS,
@@ -477,7 +479,7 @@ static void coroutine_fn mirror_run(void *opaque)
             }
 
             assert(n > 0);
-            if (ret == 1) {
+            if (ret == 1 || mark_all_dirty) {
                 bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
             }
             sector_num += n;
@@ -767,8 +769,8 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
     base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
     mirror_start_job(bs, target, replaces,
                      speed, granularity, buf_size,
-                     on_source_error, on_target_error, unmap, cb, opaque, errp,
-                     &mirror_job_driver, is_none_mode, base);
+                     on_source_error, on_target_error, unmap,
+                     cb, opaque, errp, &mirror_job_driver, is_none_mode, base);
 }
 
 void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
-- 
1.9.3