Am 21.05.2015 um 07:47 hat Wen Congyang geschrieben: > On 05/09/2015 01:21 AM, Kevin Wolf wrote: > > For bs->file, using references to existing BDSes has been possible for a > > while already. This patch enables the same for bs->backing_hd. > > 1. We reference to an existing BDSes, and some disk uses this blk. Do > we allow this?
Currently yes. If it breaks, you get to keep both pieces. As long as your guest device is read-only, it should just work. It would be a very bad idea, though, to write to a backing file. Op blockers should eventually prevent this from happening (Jeff, you may want to take a note ;-)) > 2. bs->backing_hd->blk can be not NULL now? If we do an active commit > to this backing file(use mirror job), we will call bdrv_swap() in > mirror_exit(), and the function bdrv_swap() doesn't allow that > new_bs->blk(here is bs->backing_hd) is not NULL. You're right. I can remove this patch from the series for now, but of course that doesn't solve the problem. I'm not sure what to do about it. Making bdrv_swap() work with BDSes that have BB attached is probably another item in the list of "dynamic reconfiguration" problems. Markus, any ideas? Kevin
