Commit d1f0132e authored by Mark McLoughlin's avatar Mark McLoughlin Committed by Rusty Russell
Browse files

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: default avatarMark McLoughlin <>
Signed-off-by: default avatarRusty Russell <>
parent b60da13f
......@@ -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! */
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,
= 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)
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. */
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