diff options
| -rw-r--r-- | block/backup.c | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/block/backup.c b/block/backup.c index 76addef3dc..0f1b1bc084 100644 --- a/block/backup.c +++ b/block/backup.c @@ -501,6 +501,8 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target, BlockJobTxn *txn, Error **errp) { int64_t len; + BlockDriverInfo bdi; + int ret; assert(bs); assert(target); @@ -570,15 +572,32 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target, goto error; } - bdrv_op_block_all(target, job->common.blocker); - job->on_source_error = on_source_error; job->on_target_error = on_target_error; job->target = target; job->sync_mode = sync_mode; job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ? sync_bitmap : NULL; - job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT; + + /* If there is no backing file on the target, we cannot rely on COW if our + * backup cluster size is smaller than the target cluster size. Even for + * targets with a backing file, try to avoid COW if possible. */ + ret = bdrv_get_info(job->target, &bdi); + if (ret < 0 && !target->backing) { + 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"); + goto error; + } else if (ret < 0 && target->backing) { + /* Not fatal; just trudge on ahead. */ + job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT; + } else { + job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size); + } + + bdrv_op_block_all(target, job->common.blocker); job->common.len = len; job->common.co = qemu_coroutine_create(backup_run); block_job_txn_add_job(txn, &job->common); |