[Qemu-devel] [PATCH v6 26/42] backup: Deal with filters

[Max Reitz <mreitz@redhat.com>]

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/backup.c |  9 +++++----
 blockdev.c     | 19 +++++++++++++++----
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index ecadb61af3..7854d7575b 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -611,6 +611,7 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 {
     int ret;
     BlockDriverInfo bdi;
+    bool target_does_cow = bdrv_backing_chain_next(target);
 
     /*
      * If there is no backing file on the target, we cannot rely on COW if our
@@ -618,7 +619,7 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
      * targets with a backing file, try to avoid COW if possible.
      */
     ret = bdrv_get_info(target, &bdi);
-    if (ret == -ENOTSUP && !target->backing) {
+    if (ret == -ENOTSUP && !target_does_cow) {
         /* Cluster size is not defined */
         warn_report("The target block device doesn't provide "
                     "information about the block size and it doesn't have a "
@@ -627,14 +628,14 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
                     "this default, the backup may be unusable",
                     BACKUP_CLUSTER_SIZE_DEFAULT);
         return BACKUP_CLUSTER_SIZE_DEFAULT;
-    } else if (ret < 0 && !target->backing) {
+    } else if (ret < 0 && !target_does_cow) {
         error_setg_errno(errp, -ret,
             "Couldn't determine the cluster size of the target image, "
             "which has no backing file");
         error_append_hint(errp,
             "Aborting, since this may create an unusable destination image\n");
         return ret;
-    } else if (ret < 0 && target->backing) {
+    } else if (ret < 0 && target_does_cow) {
         /* Not fatal; just trudge on ahead. */
         return BACKUP_CLUSTER_SIZE_DEFAULT;
     }
@@ -683,7 +684,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         return NULL;
     }
 
-    if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
+    if (compress && !bdrv_supports_compressed_writes(target)) {
         error_setg(errp, "Compression is not supported for this drive %s",
                    bdrv_get_device_name(target));
         return NULL;
diff --git a/blockdev.c b/blockdev.c
index c451f553f7..c6f79b4e0e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3656,7 +3656,13 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
     /* See if we have a backing HD we can use to create our new image
      * on top of. */
     if (backup->sync == MIRROR_SYNC_MODE_TOP) {
-        source = backing_bs(bs);
+        /*
+         * Backup will not replace the source by the target, so none
+         * of the filters skipped here will be removed (in contrast to
+         * mirror).  Therefore, we can skip all of them when looking
+         * for the first COW relationship.
+         */
+        source = bdrv_filtered_cow_bs(bdrv_skip_rw_filters(bs));
         if (!source) {
             backup->sync = MIRROR_SYNC_MODE_FULL;
         }
@@ -3676,9 +3682,14 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
     if (backup->mode != NEW_IMAGE_MODE_EXISTING) {
         assert(backup->format);
         if (source) {
-            bdrv_refresh_filename(source);
-            bdrv_img_create(backup->target, backup->format, source->filename,
-                            source->drv->format_name, NULL,
+            /* Implicit filters should not appear in the filename */
+            BlockDriverState *explicit_backing =
+                bdrv_skip_implicit_filters(source);
+
+            bdrv_refresh_filename(explicit_backing);
+            bdrv_img_create(backup->target, backup->format,
+                            explicit_backing->filename,
+                            explicit_backing->drv->format_name, NULL,
                             size, flags, false, &local_err);
         } else {
             bdrv_img_create(backup->target, backup->format, NULL, NULL, NULL,
-- 
2.21.0