mirror: Fix bdrv_has_zero_init() use

bdrv_has_zero_init() only has meaning for newly created images or image
areas.  If the mirror job itself did not create the image, it cannot
rely on bdrv_has_zero_init()'s result to carry any meaning.

This is the case for drive-mirror with mode=existing and always for
blockdev-mirror.

Note that we only have to zero-initialize the target with sync=full,
because other modes actually do not promise that the target will contain
the same data as the source after the job -- sync=top only promises to
copy anything allocated in the top layer, and sync=none will only copy
new I/O.  (Which is how mirror has always handled it.)

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190724171239.8764-3-mreitz@redhat.com
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/blockdev.c b/blockdev.c
index 2e536dde3e..fbef6845c8 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3782,6 +3782,7 @@ static void blockdev_mirror_common(const char *job_id, BlockDriverState *bs,
                                    bool has_replaces, const char *replaces,
                                    enum MirrorSyncMode sync,
                                    BlockMirrorBackingMode backing_mode,
+                                   bool zero_target,
                                    bool has_speed, int64_t speed,
                                    bool has_granularity, uint32_t granularity,
                                    bool has_buf_size, int64_t buf_size,
@@ -3890,7 +3891,7 @@ static void blockdev_mirror_common(const char *job_id, BlockDriverState *bs,
      */
     mirror_start(job_id, bs, target,
                  has_replaces ? replaces : NULL, job_flags,
-                 speed, granularity, buf_size, sync, backing_mode,
+                 speed, granularity, buf_size, sync, backing_mode, zero_target,
                  on_source_error, on_target_error, unmap, filter_node_name,
                  copy_mode, errp);
 }
@@ -3906,6 +3907,7 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
     int flags;
     int64_t size;
     const char *format = arg->format;
+    bool zero_target;
     int ret;
 
     bs = qmp_get_root_bs(arg->device, errp);
@@ -4007,6 +4009,10 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
         goto out;
     }
 
+    zero_target = (arg->sync == MIRROR_SYNC_MODE_FULL &&
+                   (arg->mode == NEW_IMAGE_MODE_EXISTING ||
+                    !bdrv_has_zero_init(target_bs)));
+
     ret = bdrv_try_set_aio_context(target_bs, aio_context, errp);
     if (ret < 0) {
         bdrv_unref(target_bs);
@@ -4015,7 +4021,8 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
 
     blockdev_mirror_common(arg->has_job_id ? arg->job_id : NULL, bs, target_bs,
                            arg->has_replaces, arg->replaces, arg->sync,
-                           backing_mode, arg->has_speed, arg->speed,
+                           backing_mode, zero_target,
+                           arg->has_speed, arg->speed,
                            arg->has_granularity, arg->granularity,
                            arg->has_buf_size, arg->buf_size,
                            arg->has_on_source_error, arg->on_source_error,
@@ -4055,6 +4062,7 @@ void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
     AioContext *aio_context;
     BlockMirrorBackingMode backing_mode = MIRROR_LEAVE_BACKING_CHAIN;
     Error *local_err = NULL;
+    bool zero_target;
     int ret;
 
     bs = qmp_get_root_bs(device, errp);
@@ -4067,6 +4075,8 @@ void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
         return;
     }
 
+    zero_target = (sync == MIRROR_SYNC_MODE_FULL);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -4077,7 +4087,7 @@ void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
 
     blockdev_mirror_common(has_job_id ? job_id : NULL, bs, target_bs,
                            has_replaces, replaces, sync, backing_mode,
-                           has_speed, speed,
+                           zero_target, has_speed, speed,
                            has_granularity, granularity,
                            has_buf_size, buf_size,
                            has_on_source_error, on_source_error,