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Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush req
From: |
Paul Brook |
Subject: |
Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request |
Date: |
Fri, 28 Mar 2008 16:40:54 +0000 |
User-agent: |
KMail/1.9.9 |
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.
Paul
- [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Marcelo Tosatti, 2008/03/28
- Re: [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Jamie Lokier, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Marcelo Tosatti, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request,
Paul Brook <=
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Marcelo Tosatti, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Paul Brook, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Marcelo Tosatti, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Jamie Lokier, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Paul Brook, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Jamie Lokier, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Paul Brook, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Jamie Lokier, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Marcelo Tosatti, 2008/03/28
- Re: [kvm-devel] [Qemu-devel] [PATCH] QEMU: fsync AIO writes on flush request, Jamie Lokier, 2008/03/28