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

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Message-ID: <20120730134424.GC6041@lst.de>
Date:	Mon, 30 Jul 2012 15:44:24 +0200
From:	Christoph Hellwig <hch@....de>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Asias He <asias@...hat.com>, 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

On Mon, Jul 30, 2012 at 09:31:06AM +0200, Paolo Bonzini wrote:
> 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.

A bio-based driver needs to handle both REQ_FLUSH and REQ_FUA as it does
not get the sequencing of REQ_FUA into REQ_FLUSH that request based drivers
can request.  To what the REQ_FUA request gets translated is a different story.
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