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Date: Fri, 9 May 2014 10:22:18 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140509082218.GC12865@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 18/25] rbd: use BlockDriverState's
 AioContext
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To: Josh Durgin <josh.durgin@inktank.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>

On Thu, May 08, 2014 at 05:04:16PM -0700, Josh Durgin wrote:
> On 05/08/2014 07:34 AM, Stefan Hajnoczi wrote:
> >Drop the assumption that we're using the main AioContext.  Convert
> >qemu_bh_new() to aio_bh_new() and qemu_aio_wait() to aio_poll().
> >
> >The .bdrv_detach_aio_context() and .bdrv_attach_aio_context() interfaces
> >are not needed since no fd handlers, timers, or BHs stay registered when
> >requests have been drained.
> >
> >Cc: Josh Durgin <josh.durgin@inktank.com>
> >Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> >---
> >  block/rbd.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> >diff --git a/block/rbd.c b/block/rbd.c
> >index dbc79f4..41f7bdc 100644
> >--- a/block/rbd.c
> >+++ b/block/rbd.c
> >@@ -548,7 +548,7 @@ static void qemu_rbd_aio_cancel(BlockDriverAIOCB *blockacb)
> >      acb->cancelled = 1;
> >
> >      while (acb->status == -EINPROGRESS) {
> >-        qemu_aio_wait();
> >+        aio_poll(bdrv_get_aio_context(acb->common.bs), true);
> >      }
> >
> >      qemu_aio_release(acb);
> >@@ -581,7 +581,8 @@ static void rbd_finish_aiocb(rbd_completion_t c, RADOSCB *rcb)
> >      rcb->ret = rbd_aio_get_return_value(c);
> >      rbd_aio_release(c);
> >
> >-    acb->bh = qemu_bh_new(rbd_finish_bh, rcb);
> >+    acb->bh = aio_bh_new(bdrv_get_aio_context(acb->common.bs),
> >+                         rbd_finish_bh, rcb);
> >      qemu_bh_schedule(acb->bh);
> >  }
> 
> Assuming bdrv_get_aio_context() continues to be safe to call from a
> non-qemu thread:
> 
> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

Yes, we're running in the AioContext associated with this
BlockDriverState.  This effectively means we have a lock on the
BlockDriverState.