Re: [Qemu-devel] [RFC PATCH 2/3] sheepdog: pass NULL for io_flush

[Kevin Wolf]

Am 08.04.2013 um 17:31 hat Stefan Hajnoczi geschrieben:
> On Tue, Apr 02, 2013 at 10:37:24AM +0200, Kevin Wolf wrote:
> > Am 28.03.2013 um 22:52 hat Anthony Liguori geschrieben:
> > > Signed-off-by: Anthony Liguori <address@hidden>
> > > ---
> > >  block/sheepdog.c | 11 ++---------
> > >  1 file changed, 2 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/block/sheepdog.c b/block/sheepdog.c
> > > index bb67c4c..2bccd9b 100644
> > > --- a/block/sheepdog.c
> > > +++ b/block/sheepdog.c
> > > @@ -503,13 +503,6 @@ static void restart_co_req(void *opaque)
> > >      qemu_coroutine_enter(co, NULL);
> > >  }
> > >  
> > > -static int have_co_req(void *opaque)
> > > -{
> > > -    /* this handler is set only when there is a pending request, so
> > > -     * always returns 1. */
> > 
> > Now you return 1 even when no request is pending (which is the case in
> > which no io_flush handler would be set before). Why is this correct?
> > (This is actually a question about PATCH 1/3, I just noticed it here.
> > Are there more cases like this?)
> 
> The trick with return 1 handlers is that they are deleted when there are
> no more requests.  The pattern is:
> 
> ...begin processing request...
> qemu_set_fd_handler2(fd, ..., have_co_req);
> qemu_coroutine_yield()
> qemu_set_fd_handler2(fd, NULL, NULL, NULL, NULL); /* delete handler */
> ...finish processing request...

Indeed. I thought I had seen a case where only the flush handler is
reset, but it seems I didn't look close enough.

Kevin