Am 28.02.2017 um 20:33 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 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>
> ---
>
> v4: use error_report()
> add article
>
> v3: fix compilation (I feel like an idiot)
> adjust wording (Fam)
>
> v2: add WARNING
>
> ===
>
> 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
>
> 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 | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/block/backup.c b/block/backup.c
> index ea38733849..ea160e9e82 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -24,6 +24,7 @@
> #include "qemu/cutils.h"
> #include "sysemu/block-backend.h"
> #include "qemu/bitmap.h"
> +#include "qemu/error-report.h"
>
> #define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
> #define SLICE_TIME 100000000ULL /* ns */
> @@ -638,7 +639,16 @@ 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) {
I think this should be if (ret == -ENOTSUP && !target->backing) because
the warning explicitly says "doesn't have a backing file", and the case
with a backing file is already handled below (without a warning).
I can fix this while applying if you agree.
> + /* Cluster size is not defined */
> + error_report("WARNING: 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");
Kevin
