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 <vsement...@virtuozzo.com> > --- > > 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 | 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 >