From: Christoph Hellwig <hch@lst.de>
To: Jamie Lokier <jamie@shareable.org>
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
hch@lst.de
Subject: Re: [Qemu-devel] [PATCH] virtio-spec: document block CMD and FLUSH
Date: Tue, 4 May 2010 20:56:14 +0200 [thread overview]
Message-ID: <20100504185614.GB24998@lst.de> (raw)
In-Reply-To: <20100420014635.GE21899@shareable.org>
On Tue, Apr 20, 2010 at 02:46:35AM +0100, Jamie Lokier wrote:
> Does this mean that virtio-blk supports all three combinations?
>
> 1. FLUSH that isn't a barrier
> 2. FLUSH that is also a barrier
> 3. Barrier that is not a flush
>
> 1 is good for fsync-like operations;
> 2 is good for journalling-like ordered operations.
> 3 sounds like it doesn't mean a lot as the host cache provides no
> guarantees and has no ordering facility that can be used.
No. The Linux virtio_blk guest driver either supports data integrity
by using FLUSH or can send down BARRIER requests which aren't much
help at all. Qemu only implements FLUSH anyway.
next prev parent reply other threads:[~2010-05-04 18:56 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-18 22:22 [Qemu-devel] [PATCH] virtio-spec: document block CMD and FLUSH Michael S. Tsirkin
2010-04-19 21:26 ` [Qemu-devel] " Michael S. Tsirkin
2010-04-28 15:52 ` Michael S. Tsirkin
2010-04-20 1:46 ` [Qemu-devel] " Jamie Lokier
2010-04-20 13:22 ` Paul Brook
2010-04-21 10:39 ` Michael S. Tsirkin
2010-05-04 18:56 ` Christoph Hellwig [this message]
2010-05-04 19:01 ` Michael S. Tsirkin
2010-05-04 4:38 ` [Qemu-devel] " Rusty Russell
2010-05-04 6:56 ` Stefan Hajnoczi
2010-05-04 8:34 ` Avi Kivity
2010-05-04 8:41 ` Jens Axboe
2010-05-04 20:17 ` Jamie Lokier
2010-05-05 4:58 ` Rusty Russell
2010-05-05 6:03 ` Neil Brown
2010-05-06 6:05 ` Rusty Russell
2010-05-06 14:57 ` Jamie Lokier
2010-05-06 15:25 ` Jamie Lokier
2010-05-04 10:05 ` Christoph Hellwig
2010-05-04 20:32 ` Jamie Lokier
2010-05-04 18:54 ` Christoph Hellwig
2010-05-04 18:56 ` Michael S. Tsirkin
2010-05-04 18:58 ` Michael S. Tsirkin
2010-05-05 5:00 ` Rusty Russell
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