lguest: wrap last_avail accesses.

To simplify the transition to when we publish indices in the ring
(and make shuffling my patch queue easier), wrap them in a lg_last_avail()
macro.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 11 insertions, 5 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index a1fca9db788e..31a688e105ca 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -191,6 +191,9 @@ static void *_convert(struct iovec *iov, size_t size, size_t align,
         return iov->iov_base;
 }
 
+/* Wrapper for the last available index.  Makes it easier to change. */
+#define lg_last_avail(vq)       ((vq)->last_avail_idx)
+
 /* The virtio configuration space is defined to be little-endian.  x86 is
  * little-endian too, but it's nice to be explicit so we have these helpers. */
 #define cpu_to_le16(v16) (v16)
@@ -690,19 +693,22 @@ static unsigned get_vq_desc(struct virtqueue *vq,
                             unsigned int *out_num, unsigned int *in_num)
 {
         unsigned int i, head;
+        u16 last_avail;
 
         /* Check it isn't doing very strange things with descriptor numbers. */
-        if ((u16)(vq->vring.avail->idx - vq->last_avail_idx) > vq->vring.num)
+        last_avail = lg_last_avail(vq);
+        if ((u16)(vq->vring.avail->idx - last_avail) > vq->vring.num)
                 errx(1, "Guest moved used index from %u to %u",
-                     vq->last_avail_idx, vq->vring.avail->idx);
+                     last_avail, vq->vring.avail->idx);
 
         /* If there's nothing new since last we looked, return invalid. */
-        if (vq->vring.avail->idx == vq->last_avail_idx)
+        if (vq->vring.avail->idx == last_avail)
                 return vq->vring.num;
 
         /* Grab the next descriptor number they're advertising, and increment
          * the index we've seen. */
-        head = vq->vring.avail->ring[vq->last_avail_idx++ % vq->vring.num];
+        head = vq->vring.avail->ring[last_avail % vq->vring.num];
+        lg_last_avail(vq)++;
 
         /* If their number is silly, that's a fatal mistake. */
         if (head >= vq->vring.num)
@@ -980,7 +986,7 @@ static void update_device_status(struct device *dev)
                 for (vq = dev->vq; vq; vq = vq->next) {
                         memset(vq->vring.desc, 0,
                                vring_size(vq->config.num, getpagesize()));
-                        vq->last_avail_idx = 0;
+                        lg_last_avail(vq) = 0;
                 }
         } else if (dev->desc->status & VIRTIO_CONFIG_S_FAILED) {
                 warnx("Device %s configuration FAILED", dev->name);