Am 23.04.2015 um 12:05 hat Paolo Bonzini geschrieben: > > > On 23/04/2015 11:14, Wen Congyang wrote: > > The bs->file->driver should support backing file, and use backing reference > > already. > > > > What about the primary side? We should control when to connect to NBD > > server, > > not in nbd_open().
Why do you need to create the block device before the connection should be made? > My naive suggestion could be to add a BDRV_O_NO_CONNECT option to > bdrv_open and a separate bdrv_connect callback. Open would fail if > BDRV_O_NO_CONNECT is specified and drv->bdrv_connect is NULL. > > You would then need a way to have quorum pass BDRV_O_NO_CONNECT. Please don't add new flags. If we have to, we can introduce a new option (in the QDict), but first let's check if it's really necessary. > Perhaps quorum is not a great match after all, and it's better to add a > new "colo" driver similar to quorum but simpler and only using the read > policy that you need for colo. The new driver would also know how to > use BDRV_O_NO_CONNECT. In any case the amount of work needed would not > be too big. I thought the same, but haven't looked at the details yet. But if I understand correctly, the plan is to take quorum and add options to turn off the functionality of using a quorum - that's a bit odd. What I think is really needed here is essentially an active mirror filter. Kevin