Re: [PATCH v2 2/4] vhost: Drop variable last_avail_idx in vhost_get_vq_desc()

[Gavin Shan]

On 4/30/24 04:45, Michael S. Tsirkin wrote:
> On Mon, Apr 29, 2024 at 08:13:58PM +1000, Gavin Shan wrote:
> > The local variable @last_avail_idx is equivalent to vq->last_avail_idx.
> > So the code can be simplified a bit by dropping the local variable
> > @last_avail_idx.
> >
> > No functional change intended.
> >
> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> > ---
> >   drivers/vhost/vhost.c | 7 +++----
> >   1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 7aa623117aab..b278c0333a66 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2524,7 +2524,6 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   {
> >   	struct vring_desc desc;
> >   	unsigned int i, head, found = 0;
> > -	u16 last_avail_idx = vq->last_avail_idx;
> >   	__virtio16 ring_head;
> >   	int ret, access;
> >   
> > @@ -2539,10 +2538,10 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   
> >   	/* Grab the next descriptor number they're advertising, and increment
> >   	 * the index we've seen. */
> > -	if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
> > +	if (unlikely(vhost_get_avail_head(vq, &ring_head, vq->last_avail_idx))) {
> >   		vq_err(vq, "Failed to read head: idx %d address %p\n",
> > -		       last_avail_idx,
> > -		       &vq->avail->ring[last_avail_idx % vq->num]);
> > +		       vq->last_avail_idx,
> > +		       &vq->avail->ring[vq->last_avail_idx % vq->num]);
> >   		return -EFAULT;
> >   	}
>
> I don't see the big advantage and the line is long now.

The point is to avoid the local variable @last_avail_idx since it's equivalent
to vq->last_avail_idx, as stated in the commit log. Besides, it paves the way
for PATCH[v2 3/4] where the whole logic fetching the head and sanity check is
moved to vhost_get_avail_head(), so that vhost_get_vq_desc() is simplified

I will drop PATCH[2, 3, 4] as you suggested.

Thanks,
Gavin