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Re: [Qemu-devel] [PATCH v2] backup: allow target without .bdrv_get_info
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v2] backup: allow target without .bdrv_get_info |
Date: |
Wed, 15 Feb 2017 19:33:24 +0800 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Wed, 02/15 14:09, 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 <address@hidden>
> ---
>
> v2: add WARNING
>
> ===
>
> Since commit
>
> commit 4c9bca7e39a6e07ad02c1dcde3478363344ec60b
> Author: John Snow <address@hidden>
> Date: Thu Feb 25 15:58:30 2016 -0500
>
> block/backup: avoid copying less than full target clusters
>
> 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.
If you respin, including above in the commit message is even better, IMO.
>
> 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 | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/block/backup.c b/block/backup.c
> index ea38733..a464b63 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -638,7 +638,15 @@ 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 */
> + error_report("WARNING: Target block device doesn't provide
> information "
> + "about block size and it doesn't have backing file. "
> + "Default block size of %u bytes is used. If actual
> block "
> + "size of target exceeds this default, destination image
> "
> + "may become unusable");
"Image unusable" might be too strong here because it sounds like a serious
damage to the image, while actually what we mean is "backup unusable".
> + 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");
> --
> 1.8.3.1
>
Fam