Am 25.10.2016 um 15:53 hat Paolo Bonzini geschrieben: > > > On 25/10/2016 15:39, Alberto Garcia wrote: > > On Mon 24 Oct 2016 12:53:41 PM CEST, Paolo Bonzini wrote: > > > >>> My first thoughts were about how to let an unpause succeed without a > >>> previous pause for these objects, but actually I think this isn't > >>> what we should do. We rather want to actually do the pause instead > >>> because even new BDSes and block jobs should probably start in a > >>> quiesced state when created inside a drain_all section. > >> > >> Yes, I agree with this. It shouldn't be too hard to implement it. It > >> would require a BlockDriverState to look at the global "inside > >> bdrv_drain_all_begin" state, and ask its BlockBackend to disable > >> itself upon bdrv_replace_child. > > > > Why in bdrv_replace_child()? bdrv_drain_all_end() enables all BDSs, but > > if you add one with "blockdev-add" it's not going to be disabled using > > this method. > > You only need to disable it when blk_insert_bs is called. In fact...
This assumes that the block driver doesn't issue internal background I/O by itself. Probably true for everything that we have today, but it would probably be cleaner to quiesce it directly in bdrv_open_common(). > > In addition to that block jobs need the same, don't they? Something like > > "job->pause_count = all_quiesce_counter" in the initialization. > > ... we discussed a couple weeks ago that block jobs should register > BlkDeviceOps that pause the job in the drained_begin callback. So when > the block job calls blk_insert_bs, the drained_begin callback would > start the job as paused. Yes, should, but doing this kind of infrastructure work isn't something for this series. > > I think we'd also need to add block_job_pause_point() at the beginning > > of each one of their coroutines, in order to make sure that they really > > start paused. > > It depends on the job, for example streaming starts with > block_job_sleep_ns. Commit also does, except for some blk_getlength and > blk_truncate calls that could be moved to the caller. Kevin