From: Avi Kivity <avi@redhat.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: "Richard W.M. Jones" <rjones@redhat.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks.
Date: Sat, 05 Dec 2009 19:31:05 +0200 [thread overview]
Message-ID: <4B1A98D9.7010408@redhat.com> (raw)
In-Reply-To: <4B198D5B.5080803@codemonkey.ws>
On 12/05/2009 12:29 AM, Anthony Liguori wrote:
>
> Well disk sharing isn't actually bad as long as it's raw or a physical
> device.
>
> For qcow2, it's very complicated by backing files because we really
> need to express the concept of a read-write lock.
>
> That is, as long as the guests are opening the file read only, you
> should allow many readers. However, you should prevent anyone from
> opening with write permission. Likewise, writes should prevent future
> reads.
>
Well shared/exclusive or read/write locks support exactly that.
For non-raw storage we should take the locks unconditionally, since
there is no useful way to share such images opened for write access.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2009-12-05 17:31 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-04 16:53 [Qemu-devel] [PATCH] Disk image shared and exclusive locks Richard W.M. Jones
2009-12-04 17:15 ` Anthony Liguori
2009-12-04 21:57 ` Richard W.M. Jones
2009-12-04 22:29 ` Anthony Liguori
2009-12-05 17:31 ` Avi Kivity [this message]
2009-12-05 17:47 ` Anthony Liguori
2009-12-05 17:55 ` Avi Kivity
2009-12-05 17:59 ` Anthony Liguori
2009-12-07 10:31 ` Jamie Lokier
2009-12-07 10:42 ` Kevin Wolf
2009-12-07 10:48 ` Avi Kivity
2009-12-07 10:56 ` Kevin Wolf
2009-12-07 11:28 ` Jamie Lokier
2009-12-07 11:51 ` Kevin Wolf
2009-12-07 12:06 ` Daniel P. Berrange
2009-12-07 10:45 ` Daniel P. Berrange
2009-12-07 11:19 ` Jamie Lokier
2009-12-07 11:30 ` Daniel P. Berrange
2009-12-07 11:31 ` Richard W.M. Jones
2009-12-07 11:38 ` Jamie Lokier
2009-12-07 11:49 ` Daniel P. Berrange
2009-12-07 11:59 ` Richard W.M. Jones
2009-12-07 14:35 ` [Qemu-devel] " Paolo Bonzini
2009-12-07 13:43 ` [Qemu-devel] " Anthony Liguori
2009-12-07 14:01 ` Daniel P. Berrange
2009-12-07 14:15 ` Anthony Liguori
2009-12-07 14:28 ` Daniel P. Berrange
2009-12-07 14:53 ` Anthony Liguori
2009-12-08 9:40 ` Kevin Wolf
2009-12-07 11:04 ` Richard W.M. Jones
2009-12-07 10:58 ` Richard W.M. Jones
2009-12-07 11:35 ` Jamie Lokier
2009-12-07 13:39 ` Anthony Liguori
2009-12-07 14:08 ` Richard W.M. Jones
2009-12-07 14:22 ` Anthony Liguori
2009-12-07 14:31 ` Richard W.M. Jones
2009-12-07 14:55 ` Anthony Liguori
2009-12-08 9:48 ` Kevin Wolf
2009-12-08 10:16 ` Richard W.M. Jones
2009-12-07 14:38 ` [Qemu-devel] " Paolo Bonzini
2009-12-07 9:38 ` [Qemu-devel] " Daniel P. Berrange
2009-12-07 10:39 ` Chris Webb
2009-12-07 13:32 ` Anthony Liguori
2009-12-07 13:38 ` Chris Webb
2009-12-07 13:47 ` Anthony Liguori
2009-12-07 14:25 ` Daniel P. Berrange
2009-12-07 14:58 ` Chris Webb
2009-12-07 14:16 ` [Qemu-devel] [PATCH VERSION 2] " Richard W.M. Jones
2009-12-07 15:06 ` Anthony Liguori
2009-12-08 8:48 ` [Qemu-devel] " Paolo Bonzini
2009-12-08 10:00 ` [Qemu-devel] " Kevin Wolf
2009-12-08 10:25 ` Richard W.M. Jones
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