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Re: [Qemu-block] [PATCH v3] backup: allow target without .bdrv_get_info
From: |
Jeff Cody |
Subject: |
Re: [Qemu-block] [PATCH v3] backup: allow target without .bdrv_get_info |
Date: |
Wed, 15 Feb 2017 12:04:30 -0500 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, Feb 15, 2017 at 05:58:13PM +0300, 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>
> ---
>
> v3: fix compilation (I feel like an idiot)
> adjust wording (Fam)
>
> 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.
>
> 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 | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/block/backup.c b/block/backup.c
> index ea38733..d800a24 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -638,7 +638,16 @@ 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 */
> + fprintf(stderr,
> + "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, backup may be unusable",
> + BACKUP_CLUSTER_SIZE_DEFAULT);
You should use error_report, like in your v2 patch. Just make sure to
include qemu/error-report.h.
> + 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
>