On Thu, Oct 15, 2015 at 10:19:17AM +0800, Wen Congyang wrote: > On 10/14/2015 10:27 PM, Stefan Hajnoczi wrote: > > On Tue, Oct 13, 2015 at 05:08:17PM +0800, Wen Congyang wrote: > >> On 10/13/2015 12:27 AM, Stefan Hajnoczi wrote: > >>> On Fri, Sep 25, 2015 at 02:17:36PM +0800, Wen Congyang wrote: > >>>> + /* start backup job now */ > >>>> + bdrv_op_unblock(s->hidden_disk, BLOCK_OP_TYPE_BACKUP_TARGET, > >>>> + s->active_disk->backing_blocker); > >>>> + bdrv_op_unblock(s->secondary_disk, BLOCK_OP_TYPE_BACKUP_SOURCE, > >>>> + s->hidden_disk->backing_blocker); > >>> > >>> Why is it safe to unblock these operations? > >>> > >>> Why do they have to be blocked for non-replication users? > >> > >> hidden_disk and secondary disk are opened as backing file, so it is > >> blocked for > >> non-replication users. > >> What can I do if I don't unblock it and want to do backup? > > > > CCing Jeff Cody, block jobs maintainer > > > > You need to explain why it is safe remove this protection. We can't > > merge code that may be unsafe. > > > > I think we can investigate further by asking: when does QEMU code assume > > the backing file is read-only? > > The backing file is opened in read-only mode. I want to reopen it in > read-write > mode here in the next version(So the patch 1 will be dropped) > > > > > I haven't checked but these cases come to mind: > > > > Operations that move data between BDS in the backing chain (e.g. commit > > and stream block jobs) will lose or overwrite data if the backing file > > is being written to by another coroutine. > > > > We need to prevent users from running these operations at the same time. > > Yes, but qemu doesn't provide such API.
This series can't be merged unless it is safe. Have you looked at op blockers and thought about how to prevent unsafe operations? Stefan
