[Qemu-block] backup notifier fail policy

[Vladimir Sementsov-Ogievskiy]

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?

--
Best regards,
Vladimir