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Date: Wed, 04 Jun 2014 13:10:45 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 5/5] virtio-blk: Drop VirtIOBlockReq.read
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To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 04/06/2014 13:03, Fam Zheng ha scritto:
> 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?

No, but only because inhdr is a single byte.

Paolo