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Date: Wed, 4 Jun 2014 19:03:16 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 5/5] virtio-blk: Drop VirtIOBlockReq.read
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Wed, 06/04 10:42, Paolo Bonzini wrote:
> Il 04/06/2014 09:53, Fam Zheng ha scritto:
> >>> For the sake of restarting requests, we also need dataplane to populate the
> >>> "out" field for dataplane.  We can also take the occasion to change it from
> >>> "struct virtio_blk_outhdr *" to "struct virtio_blk_outhdr" for non-dataplane
> >>> and use iov_discard_front on the elem (see dataplane's process_request
> >>> function).
> >Using pointer avoids copying, what's the advantage of converting to "sturct
> >virtio_blk_outhdr" for non-dataplane code? For thread-safety?
> 
> The virtio code currently assumes that the outhdr is in its own iovec. This
> is not guaranteed by the spec, it's just that the drivers do it because QEMU
> required it.
> 

I see, thanks. Will convert it. IIUC, this also applies to inhdr? Do we need to
fix them as well?

Fam