linux-kernel - Re: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk

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Date:	Mon, 30 Jul 2012 09:31:06 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Asias He <asias@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Minchan Kim <minchan.kim@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH V3 3/3] virtio-blk: Add bio-based IO path for virtio-blk

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
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