On 11/10/2016 11:39, Kevin Wolf wrote: > Am 10.10.2016 um 18:41 hat Paolo Bonzini geschrieben: >> On 10/10/2016 17:37, Kevin Wolf wrote: >>>> + while ((job = block_job_next(job))) { >>>> + AioContext *aio_context = blk_get_aio_context(job->blk); >>>> + >>>> + aio_context_acquire(aio_context); >>>> + block_job_pause(job); >>>> + aio_context_release(aio_context); >>>> + } >>>> + >>>> bdrv_drain_all(); >>> >>> We already have a bdrv_drain_all() here, which does the same thing (and >>> more) internally, except that it resumes all jobs before it returns. >>> Maybe what we should do is split bdrv_drain_all() in a begin/end pair, >>> too. >> >> Hey, haven't I just suggested the same? :) I swear I hadn't read this >> before. >> >>> The other point I'm wondering now is whether bdrv_drain_all() should >>> have the aio_disable/enable_external() pair that bdrv_drain() has. >> >> bdrv_drain_all need not have it, but its start/end replacement should. > > Doesn't need it because it holds the AioContext lock?
No, because as soon as bdrv_drain_all exits, external file descriptors can be triggered again so I don't think the aio_disable/enable_external actually provides any protection. bdrv_drain_all should really only be used in cases where you already have some kind of "hold" on external file descriptors, like bdrv_close uses bdrv_drain(): bdrv_drained_begin(bs); /* complete I/O */ bdrv_flush(bs); bdrv_drain(bs); /* in case flush left pending I/O */ That said, because the simplest implementation of bdrv_drain_all() does bdrv_drained_all_start(); bdrv_drained_all_end(); just like bdrv_drain() does it, it's not a very interesting point. bdrv_drain_all will probably disable/enable external file descriptors, it just doesn't need that. Paolo