From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk
Date: Mon, 30 Jul 2012 09:31:06 +0200
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To: Asias He <asias@redhat.com>
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig <hch@lst.de>
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Il 30/07/2012 06:43, Asias He ha scritto:
>>
> 
> Yes. Something like this:
> 
>   qemu -drive file=foo.img,cache=writeback/unsafe
> 
> is not safe against power losses also?

cache=writeback and cache=none are safe, cache=unsafe isn't.

> I think we can add REQ_FLUSH & REQ_FUA support to bio path and that
> deserves another patch.

You only need to add REQ_FLUSH support.  The virtio-blk protocol does
not support REQ_FUA, because there's no easy way to do it in userspace.

Paolo