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block: mirror - fix full sync mode when target does not support zero init 

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.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 91ed4bc5bda7e2b09eb508b07c83f4071fe0b3c9.1443705220.git.jcody@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>
This commit is contained in:
Jeff Cody 2015-10-01 00:06:37 -04:00
parent fa500928ad
commit 5279efebcf
1 changed files with 3 additions and 1 deletions
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4
block/mirror.c
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@ -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;