On 02/14/2017 09:48 AM, Vladimir Sementsov-Ogievskiy wrote:
> Currently backup to nbd target is broken, as nbd doesn't have
> .bdrv_get_info realization.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> ---
>
> Hi all!
>
> Since commit
>
> commit 4c9bca7e39a6e07ad02c1dcde3478363344ec60b
> Author: John Snow <js...@redhat.com>
> Date: Thu Feb 25 15:58:30 2016 -0500
>
> block/backup: avoid copying less than full target clusters
>
Tch.
> backup to nbd target is broken, we have "Couldn't determine the cluster size
> of
> the target image".
>
> Proposed NBD protocol extension - NBD_OPT_INFO should finally solve this
> problem.
> But until it is not realized, we need allow backup to nbd target due to
> backward
> compatibility.
>
> Furthermore, is it entirely ok to disallow backup if bds lacks .bdrv_get_info?
> Which behavior should be default: to fail backup or to use default cluster
> size?
>
> block/backup.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/block/backup.c b/block/backup.c
> index ea38733..095a390 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -638,7 +638,10 @@ BlockJob *backup_job_create(const char *job_id,
> BlockDriverState *bs,
> * 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 < 0 && !target->backing) {
> + if (ret == -ENOTSUP) {
> + /* Cluster size is not defined */
> + job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
I realize this is necessary for backwards compatibility, but perhaps we
need a warning message that explains why this backup *may* not be usable
in the incremental/top cases.
(I think none/full should be ok?)
> + } 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");
>
--
—js
