This is more consistent with the commit block job, and it moves the code
to a place where we already have the necessary BlockBackends to resize
the base image when bdrv_truncate() is changed to require a BdrvChild.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/mirror.c | 50 ++++++++++++++++++++++----------------------------
 1 file changed, 22 insertions(+), 28 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 698a54e..13f793e 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -657,7 +657,28 @@ static void coroutine_fn mirror_run(void *opaque)
     if (s->bdev_length < 0) {
         ret = s->bdev_length;
         goto immediate_exit;
-    } else if (s->bdev_length == 0) {
+    }
+
+    /* Active commit must resize the base image if its size differs from the
+     * active layer. */
+    if (s->base == blk_bs(s->target)) {
+        int64_t base_length;
+
+        base_length = blk_getlength(s->target);
+        if (base_length < 0) {
+            ret = base_length;
+            goto immediate_exit;
+        }
+
+        if (s->bdev_length > base_length) {
+            ret = blk_truncate(s->target, s->bdev_length);
+            if (ret < 0) {
+                goto immediate_exit;
+            }
+        }
+    }
+
+    if (s->bdev_length == 0) {
         /* Report BLOCK_JOB_READY and wait for complete. */
         block_job_event_ready(&s->common);
         s->synced = true;
@@ -1058,9 +1079,7 @@ void commit_active_start(const char *job_id, BlockDriverState *bs,
                          BlockCompletionFunc *cb, void *opaque, Error **errp,
                          bool auto_complete)
 {
-    int64_t length, base_length;
     int orig_base_flags;
-    int ret;
     Error *local_err = NULL;
 
     orig_base_flags = bdrv_get_flags(base);
@@ -1069,31 +1088,6 @@ void commit_active_start(const char *job_id, BlockDriverState *bs,
         return;
     }
 
-    length = bdrv_getlength(bs);
-    if (length < 0) {
-        error_setg_errno(errp, -length,
-                         "Unable to determine length of %s", bs->filename);
-        goto error_restore_flags;
-    }
-
-    base_length = bdrv_getlength(base);
-    if (base_length < 0) {
-        error_setg_errno(errp, -base_length,
-                         "Unable to determine length of %s", base->filename);
-        goto error_restore_flags;
-    }
-
-    if (length > base_length) {
-        ret = bdrv_truncate(base, length);
-        if (ret < 0) {
-            error_setg_errno(errp, -ret,
-                            "Top image %s is larger than base image %s, and "
-                             "resize of base image failed",
-                             bs->filename, base->filename);
-            goto error_restore_flags;
-        }
-    }
-
     mirror_start_job(job_id, bs, creation_flags, base, NULL, speed, 0, 0,
                      MIRROR_LEAVE_BACKING_CHAIN,
                      on_error, on_error, true, cb, opaque, &local_err,
-- 
1.8.3.1

On 21.02.2017 15:57, Kevin Wolf wrote:
> This is more consistent with the commit block job, and it moves the code
> to a place where we already have the necessary BlockBackends to resize
> the base image when bdrv_truncate() is changed to require a BdrvChild.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/mirror.c | 50 ++++++++++++++++++++++----------------------------
>  1 file changed, 22 insertions(+), 28 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>

On Tue, 02/21 15:57, Kevin Wolf wrote:
> diff --git a/block/mirror.c b/block/mirror.c
> index 698a54e..13f793e 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -657,7 +657,28 @@ static void coroutine_fn mirror_run(void *opaque)
>      if (s->bdev_length < 0) {
>          ret = s->bdev_length;
>          goto immediate_exit;
> -    } else if (s->bdev_length == 0) {
> +    }
> +
> +    /* Active commit must resize the base image if its size differs from the
> +     * active layer. */
> +    if (s->base == blk_bs(s->target)) {
> +        int64_t base_length;
> +
> +        base_length = blk_getlength(s->target);
> +        if (base_length < 0) {
> +            ret = base_length;
> +            goto immediate_exit;
> +        }
> +
> +        if (s->bdev_length > base_length) {
> +            ret = blk_truncate(s->target, s->bdev_length);
> +            if (ret < 0) {
> +                goto immediate_exit;
> +            }
> +        }
> +    }
> +
> +    if (s->bdev_length == 0) {
>          /* Report BLOCK_JOB_READY and wait for complete. */
>          block_job_event_ready(&s->common);
>          s->synced = true;

This has a slight behavior change of commit job that previously upon resize
failure the job wouldn't start, but now it will, then immediately end with an
error. Not an problem, though.

Fam