Re: [Qemu-devel] [PATCH RFC 04/11] virtio_ring: implement endian reversal based on VERSION_1 feature.

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Oct 22, 2014 at 04:28:34PM +0200, Cornelia Huck wrote:
> On Wed, 22 Oct 2014 17:02:26 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, Oct 07, 2014 at 04:39:45PM +0200, Cornelia Huck wrote:
> > > From: Rusty Russell <rusty@rustcorp.com.au>
> > > 
> > > [Cornelia Huck: we don't need the vq->vring.num -> vq->ring_mask change]
> > > Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> > > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > > ---
> > >  drivers/virtio/virtio_ring.c |  195 ++++++++++++++++++++++++++++++------------
> > >  1 file changed, 138 insertions(+), 57 deletions(-)
> > > 
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 1cfb5ba..350c39b 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -145,42 +145,54 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
> > >  	i = 0;
> > >  	for (n = 0; n < out_sgs; n++) {
> > >  		for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
> > > -			desc[i].flags = VRING_DESC_F_NEXT;
> > > -			desc[i].addr = sg_phys(sg);
> > > -			desc[i].len = sg->length;
> > > -			desc[i].next = i+1;
> > > +			desc[i].flags = cpu_to_virtio16(vq->vq.vdev,
> > > +							  VRING_DESC_F_NEXT);
> > > +			desc[i].addr = cpu_to_virtio64(vq->vq.vdev,
> > > +							 sg_phys(sg));
> > > +			desc[i].len = cpu_to_virtio32(vq->vq.vdev,
> > > +							sg->length);
> > > +			desc[i].next = cpu_to_virtio16(vq->vq.vdev,
> > > +							 i+1);
> > >  			i++;
> > >  		}
> > >  	}
> > >  	for (; n < (out_sgs + in_sgs); n++) {
> > >  		for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
> > > -			desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> > > -			desc[i].addr = sg_phys(sg);
> > > -			desc[i].len = sg->length;
> > > -			desc[i].next = i+1;
> > > +			desc[i].flags =	cpu_to_virtio16(vq->vq.vdev,
> > > +							  VRING_DESC_F_NEXT|
> > > +							  VRING_DESC_F_WRITE);
> > > +			desc[i].addr = cpu_to_virtio64(vq->vq.vdev,
> > > +							 sg_phys(sg));
> > > +			desc[i].len = cpu_to_virtio32(vq->vq.vdev,
> > > +							sg->length);
> > > +			desc[i].next = cpu_to_virtio16(vq->vq.vdev, i+1);
> > >  			i++;
> > >  		}
> > >  	}
> > > -	BUG_ON(i != total_sg);
> > >  
> > >  	/* Last one doesn't continue. */
> > > -	desc[i-1].flags &= ~VRING_DESC_F_NEXT;
> > > +	desc[i-1].flags &= ~cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> > >  	desc[i-1].next = 0;
> > >  
> > > -	/* We're about to use a buffer */
> > > -	vq->vq.num_free--;
> > > -
> > >  	/* Use a single buffer which doesn't continue */
> > >  	head = vq->free_head;
> > > -	vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
> > > -	vq->vring.desc[head].addr = virt_to_phys(desc);
> > > +	vq->vring.desc[head].flags =
> > > +		cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT);
> > > +	vq->vring.desc[head].addr =
> > > +		cpu_to_virtio64(vq->vq.vdev, virt_to_phys(desc));
> > >  	/* kmemleak gives a false positive, as it's hidden by virt_to_phys */
> > >  	kmemleak_ignore(desc);
> > > -	vq->vring.desc[head].len = i * sizeof(struct vring_desc);
> > > +	vq->vring.desc[head].len =
> > > +		cpu_to_virtio32(vq->vq.vdev, i * sizeof(struct vring_desc));
> > >  
> > > -	/* Update free pointer */
> > > +	BUG_ON(i != total_sg);
> > > +
> > 
> > Why move the BUG_ON here?
> > I think I'll move it back ...
> 
> IIRC this was in the original patch I applied - but you're right, the
> statement can stay in the old place.

I think I'll do it more gradually: mechanically add accessors
everywhere as a 1st step. Split long lines and other cleanup
as a second step.

> > 
> > > +	/* Update free pointer (we store this in native endian) */
> > >  	vq->free_head = vq->vring.desc[head].next;
> > >  
> > > +	/* We've just used a buffer */
> > > +	vq->vq.num_free--;
> > > +
> > >  	return head;
> > >  }
> > >