Re: [Qemu-block] [PATCH v4] backup: allow target without .bdrv_get_info

[Vladimir Sementsov-Ogievskiy]

07.03.2017 16:47, Kevin Wolf wrote:
> 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 <address@hidden>
> > ---
> >
> > 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 <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 | 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.

Ok. no problem

> > +        /* 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


--
Best regards,
Vladimir