lguest: add support for indirect ring entries

Support the VIRTIO_RING_F_INDIRECT_DESC feature.

This is a simple matter of changing the descriptor walking
code to operate on a struct vring_desc* and supplying it
with an indirect table if detected.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 29 insertions, 12 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index bb5e3c28d9d6..9ebcd6ef361b 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -536,20 +536,21 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
 /* Each buffer in the virtqueues is actually a chain of descriptors.  This
  * function returns the next descriptor in the chain, or vq->vring.num if we're
  * at the end. */
-static unsigned next_desc(struct virtqueue *vq, unsigned int i)
+static unsigned next_desc(struct vring_desc *desc,
+                          unsigned int i, unsigned int max)
 {
         unsigned int next;
 
         /* If this descriptor says it doesn't chain, we're done. */
-        if (!(vq->vring.desc[i].flags & VRING_DESC_F_NEXT))
-                return vq->vring.num;
+        if (!(desc[i].flags & VRING_DESC_F_NEXT))
+                return max;
 
         /* Check they're not leading us off end of descriptors. */
-        next = vq->vring.desc[i].next;
+        next = desc[i].next;
         /* Make sure compiler knows to grab that: we don't want it changing! */
         wmb();
 
-        if (next >= vq->vring.num)
+        if (next >= max)
                 errx(1, "Desc next is %u", next);
 
         return next;
@@ -585,7 +586,8 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq,
                                  struct iovec iov[],
                                  unsigned int *out_num, unsigned int *in_num)
 {
-        unsigned int i, head;
+        unsigned int i, head, max;
+        struct vring_desc *desc;
         u16 last_avail = lg_last_avail(vq);
 
         while (last_avail == vq->vring.avail->idx) {
@@ -630,15 +632,28 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq,
         /* When we start there are none of either input nor output. */
         *out_num = *in_num = 0;
 
+        max = vq->vring.num;
+        desc = vq->vring.desc;
         i = head;
+
+        /* If this is an indirect entry, then this buffer contains a descriptor
+         * table which we handle as if it's any normal descriptor chain. */
+        if (desc[i].flags & VRING_DESC_F_INDIRECT) {
+                if (desc[i].len % sizeof(struct vring_desc))
+                        errx(1, "Invalid size for indirect buffer table");
+
+                max = desc[i].len / sizeof(struct vring_desc);
+                desc = check_pointer(desc[i].addr, desc[i].len);
+                i = 0;
+        }
+
         do {
                 /* Grab the first descriptor, and check it's OK. */
-                iov[*out_num + *in_num].iov_len = vq->vring.desc[i].len;
+                iov[*out_num + *in_num].iov_len = desc[i].len;
                 iov[*out_num + *in_num].iov_base
-                        = check_pointer(vq->vring.desc[i].addr,
-                                        vq->vring.desc[i].len);
+                        = check_pointer(desc[i].addr, desc[i].len);
                 /* If this is an input descriptor, increment that count. */
-                if (vq->vring.desc[i].flags & VRING_DESC_F_WRITE)
+                if (desc[i].flags & VRING_DESC_F_WRITE)
                         (*in_num)++;
                 else {
                         /* If it's an output descriptor, they're all supposed
@@ -649,9 +664,9 @@ static unsigned wait_for_vq_desc(struct virtqueue *vq,
                 }
 
                 /* If we've got too many, that implies a descriptor loop. */
-                if (*out_num + *in_num > vq->vring.num)
+                if (*out_num + *in_num > max)
                         errx(1, "Looped descriptor");
-        } while ((i = next_desc(vq, i)) != vq->vring.num);
+        } while ((i = next_desc(desc, i, max)) != max);
 
         return head;
 }
@@ -1331,6 +1346,8 @@ static void setup_tun_net(char *arg)
         add_feature(dev, VIRTIO_NET_F_HOST_TSO4);
         add_feature(dev, VIRTIO_NET_F_HOST_TSO6);
         add_feature(dev, VIRTIO_NET_F_HOST_ECN);
+        /* We handle indirect ring entries */
+        add_feature(dev, VIRTIO_RING_F_INDIRECT_DESC);
         set_config(dev, sizeof(conf), &conf);
 
         /* We don't need the socket any more; setup is done. */