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 <gs...@redhat.com>
---
  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