On 10/15/2015 10:55 PM, Stefan Hajnoczi wrote: > 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?
What about this solution: 1. unblock it in bdrv_set_backing_hd() 2. block it in qmp_block_commit(), qmp_block_stream(), qmp_block_backup()..., to prevent unsafe operations Thanks Wen Congyang > > Stefan > . >
