On Fri, Mar 28, 2008 at 04:40:54PM +0000, Paul Brook wrote:
> On Friday 28 March 2008, Marcelo Tosatti wrote:
> > On Fri, Mar 28, 2008 at 03:07:03PM +0000, Jamie Lokier wrote:
> > > Marcelo Tosatti wrote:
> > > > Its necessary to guarantee that pending AIO writes have reached stable
> > > > storage when the flush request returns.
> > > >
> > > > Also change fsync() to fdatasync(), since the modification time is not
> > > > critical data.
> > > > + if (aio_fsync(O_DSYNC, &acb->aiocb) < 0) {
> > > >
> > > > BDRVRawState *s = bs->opaque;
> > > > - fsync(s->fd);
> > > > + raw_aio_flush(bs);
> > > > + fdatasync(s->fd);
> > > > +
> > > > + /* We rely on the fact that no other AIO will be submitted
> > > > + * in parallel, but this should be fixed by per-device
> > > > + * AIO queues when allowing multiple CPU's to process IO
> > > > + * in QEMU.
> > > > + */
> > > > + qemu_aio_flush();
> > >
> > > I'm a bit confused by this. Why do you need aio_fsync(O_DSYNC) _and_
> > > synchronous fdatasync() calls? Aren't they equivalent?
> >
> > fdatasync() will write and wait for completion of dirty file data
> > present in memory.
> >
> > aio_write() only queues data for submission:
> >
> > The "asynchronous" means that this call returns as soon as the
> > request has been enqueued; the write may or may not have completed when
> > the call returns. One tests for completion using aio_error(3).
>
> Surely you should be using the normal aio notification to wait for the
> aio_fsync to complete before reporting success to the device.
qemu_aio_flush() will wait for all pending AIO requests (including
aio_fsync) to complete.
Or do you mean something else?
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