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Date: Wed, 4 Jun 2014 15:53:54 +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 Tue, 06/03 15:37, Paolo Bonzini wrote:
> I guess this is more of an RFC, but still a useful starting point for
> discussion.
> 
> Il 03/06/2014 14:52, Fam Zheng ha scritto:
> >diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> >index e406efa..74f0f32 100644
> >--- a/include/hw/virtio/virtio-blk.h
> >+++ b/include/hw/virtio/virtio-blk.h
> >@@ -146,7 +146,6 @@ typedef struct VirtIOBlockReq {
> > #ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
> >     struct VirtIOBlockDataPlane *s;
> 
> This is just dev->dataplane, so it's trivial to remove.
> 
> >     QEMUIOVector *inhdr;            /* iovecs for virtio_blk_inhdr */
> 
> This can be unified with the "in" field; the status is only one byte, so
> using a full-blown QEMUIOVector is overkill.  Stefan, what do you think?
> 
> 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?

Fam

> 
> Can you do it in v2 of this patch series?  With this in place we can look at
> the missing pieces:
> 
> - rerror/werror
> 
> - accounting (trivial)
> 
> - multiwrite (if desired).
> 
> Thanks,
> 
> Paolo
> 
> >-    bool read;                      /* read or write? */
> > #endif
> > } VirtIOBlockReq;
> >
> >
>