On Fri, Feb 09, 2018 at 06:26:41PM +0100, Paolo Bonzini wrote:
> On 09/02/2018 18:23, Kevin Wolf wrote:
> > Am 09.02.2018 um 17:28 hat Paolo Bonzini geschrieben:
> >> On 08/02/2018 18:18, Stefan Hajnoczi wrote:
> >>> + BlockDriverState *bs = blk_bs(blk);
> >>> +
> >>> + if (bs) {
> >>> + bdrv_drained_begin(bs);
> >>> + }
> >>> +
> >>> + /* We may have aio requests like -ENOMEDIUM in flight */
> >>> + while (atomic_mb_read(&blk->in_flight) > 0) {
> >>> + aio_poll(blk_get_aio_context(blk), true);
> >>> + }
> >>> +
> >>> + if (bs) {
> >>> + bdrv_drained_end(bs);
> >>
> >> This only works if you are in the default AioContext, otherwise you can
> >> run handlers for one AioContexts in two threads.
> >
> > Should aio_poll() assert that it's called in the right thread to make
> > sure we obey the rules?
> >
> >> bdrv_dec_in_flight uses bdrv_wakeup and BDRV_POLL_WHILE to ensure that
> >> this doesn't happen, so there would be more code that you have to copy
> >> into block-backend.c.
> >
> > Instead of copying, can't we generalise it into a POLL_WHILE(ctx,
> > wakeup, cond) and make BDRV_POLL_WHILE() a wrapper for that?
>
> Yes, or even move bdrv_wakeup to AioContext would do. We already have
> block layer-specific fields such as the linux-aio state(*).
>
> (*) though now that linux-aio has been improved to do something
> like epoll, there may be a better reason to place linux-aio
> state in AioContext.Thanks for the ideas, will fix in v2. Stefan
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