This patch adds the original source drive as a backing drive to our target
image so that the target image will appear complete during backup. This
is especially useful for SYNC_MODE_NONE as it allows export via NBD to
have a complete point-in-time snapshot available for export.
Signed-off-by: Ian Main <im...@redhat.com>
---
block/backup.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/block/backup.c b/block/backup.c
index 68abd23..d32b3b7 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -323,6 +323,11 @@ static void coroutine_fn backup_run(void *opaque)
hbitmap_free(job->bitmap);
+ /* Set the target backing drive back to NULL before calling delete or
+ * it will also delete the underlying drive. */
+ target->backing_hd = NULL;
+ bdrv_set_in_use(target, 0);
+
bdrv_iostatus_disable(target);
bdrv_delete(target);
@@ -362,6 +367,17 @@ void backup_start(BlockDriverState *bs, BlockDriverState
*target,
return;
}
+ /* Manually set the backing hd to be the backup source drive so
+ * that all reads done while we are backing up will be passed
+ * on to the original source drive. This allows reading from the
+ * image while the backup is in progress, or in the case of
+ * SYNC_MODE_NONE allows a complete image to be present for export.
+ * Note that we do this for all modes including SYNC_MODE_TOP as
+ * even then it allows on-the-fly reading. */
+ target->backing_hd = bs;
+ /* Set in use so it can only be exported by NBD. */
+ bdrv_set_in_use(target, 1);
+
job->on_source_error = on_source_error;
job->on_target_error = on_target_error;
job->target = target;
--
1.8.1.4
