Split out cluster_size calculation. Move copy-bitmap creation above
block-job creation, as we are going to share it with upcoming
backup-top filter, which also should be created before actual block job
creation.

Also, while being here, drop unnecessary "goto error" from
bdrv_getlength error path.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/backup.c | 84 +++++++++++++++++++++++++++++++-------------------
 1 file changed, 53 insertions(+), 31 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index b54386b699..79db4fbb6d 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -507,6 +507,42 @@ static const BlockJobDriver backup_job_driver = {
     .drain                  = backup_drain,
 };
 
+static int64_t backup_calculate_cluster_size(BlockDriverState *target,
+                                             Error **errp)
+{
+    int ret;
+    BlockDriverInfo bdi;
+
+    /*
+     * 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(target, &bdi);
+    if (ret == -ENOTSUP && !target->backing) {
+        /* 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 "
+                    "backing file. The default block size of %u bytes is "
+                    "used. If the actual block size of the target exceeds "
+                    "this default, the backup may be unusable",
+                    BACKUP_CLUSTER_SIZE_DEFAULT);
+        return BACKUP_CLUSTER_SIZE_DEFAULT;
+    } else 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");
+        return ret;
+    } else if (ret < 0 && target->backing) {
+        /* Not fatal; just trudge on ahead. */
+        return BACKUP_CLUSTER_SIZE_DEFAULT;
+    }
+
+    return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
+}
+
 BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                   BlockDriverState *target, int64_t speed,
                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
@@ -518,9 +554,10 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                   JobTxn *txn, Error **errp)
 {
     int64_t len;
-    BlockDriverInfo bdi;
     BackupBlockJob *job = NULL;
     int ret;
+    int64_t cluster_size;
+    HBitmap *copy_bitmap = NULL;
 
     assert(bs);
     assert(target);
@@ -579,9 +616,16 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     if (len < 0) {
         error_setg_errno(errp, -len, "unable to get length for '%s'",
                          bdrv_get_device_name(bs));
-        goto error;
+        return NULL;
+    }
+
+    cluster_size = backup_calculate_cluster_size(target, errp);
+    if (cluster_size < 0) {
+        return NULL;
     }
 
+    copy_bitmap = hbitmap_alloc(len, ctz32(cluster_size));
+
     /* job->len is fixed, so we can't allow resize */
     job = block_job_create(job_id, &backup_job_driver, txn, bs,
                            BLK_PERM_CONSISTENT_READ,
@@ -610,35 +654,9 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
 
     /* Detect image-fleecing (and similar) schemes */
     job->serialize_target_writes = bdrv_chain_contains(target, bs);
-
-    /* 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(target, &bdi);
-    if (ret == -ENOTSUP && !target->backing) {
-        /* 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 "
-                    "backing file. The default block size of %u bytes is "
-                    "used. If the actual block size of the target exceeds "
-                    "this default, the backup may be unusable",
-                    BACKUP_CLUSTER_SIZE_DEFAULT);
-        job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
-    } else 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);
-    }
-
-    job->copy_bitmap = hbitmap_alloc(len, ctz32(job->cluster_size));
+    job->cluster_size = cluster_size;
+    job->copy_bitmap = copy_bitmap;
+    copy_bitmap = NULL;
     job->use_copy_range = true;
     job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
                                         blk_get_max_transfer(job->target));
@@ -654,6 +672,10 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     return &job->common;
 
  error:
+    if (copy_bitmap) {
+        assert(!job || !job->copy_bitmap);
+        hbitmap_free(copy_bitmap);
+    }
     if (sync_bitmap) {
         bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
     }
-- 
2.18.0

On 15.04.19 16:49, Vladimir Sementsov-Ogievskiy wrote:
> Split out cluster_size calculation. Move copy-bitmap creation above
> block-job creation, as we are going to share it with upcoming
> backup-top filter, which also should be created before actual block job
> creation.
> 
> Also, while being here, drop unnecessary "goto error" from
> bdrv_getlength error path.

It isn’t unnecessary, though.  Before this, we invoke
bdrv_dirty_bitmap_create_successor(), so the error path has to clean
that up with bdrv_reclaim_dirty_bitmap().

Max

26.04.2019 21:30, Max Reitz wrote:
> On 15.04.19 16:49, Vladimir Sementsov-Ogievskiy wrote:
>> Split out cluster_size calculation. Move copy-bitmap creation above
>> block-job creation, as we are going to share it with upcoming
>> backup-top filter, which also should be created before actual block job
>> creation.
>>
>> Also, while being here, drop unnecessary "goto error" from
>> bdrv_getlength error path.
> 
> It isn’t unnecessary, though.  Before this, we invoke
> bdrv_dirty_bitmap_create_successor(), so the error path has to clean
> that up with bdrv_reclaim_dirty_bitmap().
> 
> Max
> 

Oops, will resend. I was looking at previous plain "return NULL", but missed
that in "if" branch we do thing to be rolled-back on fail.

Thank you for review!

-- 
Best regards,
Vladimir