On 30.09.2016 20:11, Vladimir Sementsov-Ogievskiy wrote:
Hi all!
Please, can somebody explain me, why we fail guest request in case of
io error in write notifier? I think guest consistency is more
important than success of unfinished backup. Or, what am I missing?
I'm saying about this code:
static int coroutine_fn backup_before_write_notify(
NotifierWithReturn *notifier,
void *opaque)
{
BackupBlockJob *job = container_of(notifier, BackupBlockJob,
before_write);
BdrvTrackedRequest *req = opaque;
int64_t sector_num = req->offset >> BDRV_SECTOR_BITS;
int nb_sectors = req->bytes >> BDRV_SECTOR_BITS;
assert(req->bs == blk_bs(job->common.blk));
assert((req->offset & (BDRV_SECTOR_SIZE - 1)) == 0);
assert((req->bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
return backup_do_cow(job, sector_num, nb_sectors, NULL, true);
}
So, what about something like
ret = backup_do_cow(job, ...
if (ret < 0 && job->notif_ret == 0) {
job->notif_ret = ret;
}
return 0;
and fail block job if notif_ret < 0 in other places of backup code?
And second question about notifiers in backup block job. If block job is
paused, notifiers still works and can copy data. Is it ok? So, user
thinks that job is paused, so he can do something with target disk.. But
really, this 'something' will race with write-notifiers. So, what
assumptions may user actually have about paused backup job? Is there any
agreements? Also, on query-block-jobs we will see job.busy = false, when
actually copy-on-write may be in flight..
--
Best regards,
Vladimir
