[Qemu-block] [PATCH v2] 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 | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index a258926..5d7828b 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -61,6 +61,7 @@ typedef struct MirrorBlockJob {
     int ret;
     bool unmap;
     bool waiting_for_io;
+    bool mark_all_dirty;
 } MirrorBlockJob;
 
 typedef struct MirrorOp {
@@ -477,7 +478,7 @@ static void coroutine_fn mirror_run(void *opaque)
             }
 
             assert(n > 0);
-            if (ret == 1) {
+            if (ret == 1 || s->mark_all_dirty) {
                 bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
             }
             sector_num += n;
@@ -688,7 +689,7 @@ static void mirror_start_job(BlockDriverState *bs, 
BlockDriverState *target,
                              int64_t buf_size,
                              BlockdevOnError on_source_error,
                              BlockdevOnError on_target_error,
-                             bool unmap,
+                             bool unmap, bool mark_all_dirty,
                              BlockCompletionFunc *cb,
                              void *opaque, Error **errp,
                              const BlockJobDriver *driver,
@@ -732,6 +733,7 @@ static void mirror_start_job(BlockDriverState *bs, 
BlockDriverState *target,
     s->granularity = granularity;
     s->buf_size = ROUND_UP(buf_size, granularity);
     s->unmap = unmap;
+    s->mark_all_dirty = mark_all_dirty;
 
     s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity, NULL, errp);
     if (!s->dirty_bitmap) {
@@ -757,6 +759,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
                   void *opaque, Error **errp)
 {
     bool is_none_mode;
+    bool mark_all_dirty;
     BlockDriverState *base;
 
     if (mode == MIRROR_SYNC_MODE_INCREMENTAL) {
@@ -764,11 +767,13 @@ void mirror_start(BlockDriverState *bs, BlockDriverState 
*target,
         return;
     }
     is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
+    mark_all_dirty = mode == MIRROR_SYNC_MODE_FULL &&
+                    !bdrv_has_zero_init(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, mark_all_dirty,
+                     cb, opaque, errp, &mirror_job_driver, is_none_mode, base);
 }
 
 void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
@@ -815,7 +820,7 @@ void commit_active_start(BlockDriverState *bs, 
BlockDriverState *base,
 
     bdrv_ref(base);
     mirror_start_job(bs, base, NULL, speed, 0, 0,
-                     on_error, on_error, false, cb, opaque, &local_err,
+                     on_error, on_error, false, false, cb, opaque, &local_err,
                      &commit_active_job_driver, false, base);
     if (local_err) {
         error_propagate(errp, local_err);
-- 
1.9.3