Re: [Qemu-devel] [PATCH 1/3] block: add BlockBackend->in_flight counter

[Kevin Wolf <kwolf@redhat.com>]

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?

Kevin