From: "Michael S. Tsirkin" <mst@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Sasha Levin <levinsasha928@gmail.com>,
kvm@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Marcelo Tosatti <mtosatti@redhat.com>,
Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_PIPE
Date: Mon, 4 Jul 2011 13:49:05 +0300 [thread overview]
Message-ID: <20110704104905.GC11386@redhat.com> (raw)
In-Reply-To: <4E1195A1.10103@redhat.com>
On Mon, Jul 04, 2011 at 01:27:45PM +0300, Avi Kivity wrote:
> I'd like to be able to forward an entire PCI BAR
> over a pipe. That means sending the address/data/length tuple, and
> both read and write support.
>
> >> Is the write guaranteed atomic? We probably need serialization here.
> >
> >afaik vfs_write is just a wrapper to the write() function of the
> >underlying fs so it should be atomic, no?
>
> write() isn't atomic in general. It is for pipes under certain
> circumstances, but there is no guarantee that the circumstances
> apply, or that the fd is in fact a pipe.
So the above makes it tricky to pass structured data
which is > 1 byte in size over a pipe. We could build an in-kernel API
(not sure how useful it would be for userspace) to do
an atomic write or fail (instead of a partial write),
but we'll still need to handle failures.
--
MST
next prev parent reply other threads:[~2011-07-04 10:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-03 17:04 [PATCH] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_PIPE Sasha Levin
2011-07-03 17:16 ` Avi Kivity
2011-07-03 17:44 ` Sasha Levin
2011-07-03 17:57 ` Pekka Enberg
2011-07-04 10:27 ` Avi Kivity
2011-07-04 10:49 ` Michael S. Tsirkin [this message]
2011-07-04 10:57 ` Avi Kivity
2011-07-04 14:38 ` Sasha Levin
2011-07-04 14:45 ` Avi Kivity
2011-07-04 14:52 ` Sasha Levin
2011-07-04 14:59 ` Avi Kivity
2011-07-06 4:37 ` Sasha Levin
2011-07-06 11:30 ` Avi Kivity
2011-07-04 10:32 ` Michael S. Tsirkin
2011-07-04 10:45 ` Avi Kivity
2011-07-04 11:07 ` Michael S. Tsirkin
2011-07-04 11:19 ` Avi Kivity
2011-07-04 11:45 ` Michael S. Tsirkin
2011-07-04 11:49 ` Avi Kivity
2011-07-04 12:12 ` Michael S. Tsirkin
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