[PATCH net-next RFC 1/5] vhost: split out ring head fetching logic

Jason Wang
2017-09-22T08:02:31Z

This patch splits out ring head fetching logic and leave the
descriptor fetching and translation logic. This makes it is possible
to batch fetching the descriptor indices.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/vhost.c | 75 +++++++++++++++++++++++++++++++++------------------
drivers/vhost/vhost.h | 5 ++++
2 files changed, 54 insertions(+), 26 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d6dbb28..f87ec75 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1984,41 +1984,23 @@ static int get_indirect(struct vhost_virtqueue *vq,
return 0;
}

-/* This looks in the virtqueue and for the first available buffer, and converts
- * it to an iovec for convenient access. Since descriptors consist of some
- * number of output then some number of input descriptors, it's actually two
- * iovecs, but we pack them into one and note how many of each there were.
- *
- * This function returns the descriptor number found, or vq->num (which is
- * never a valid descriptor number) if none was found. A negative code is
- * returned on error. */
-int vhost_get_vq_desc(struct vhost_virtqueue *vq,
- struct iovec iov[], unsigned int iov_size,
- unsigned int *out_num, unsigned int *in_num,
- struct vhost_log *log, unsigned int *log_num)
+static unsigned int vhost_get_vq_head(struct vhost_virtqueue *vq, int *err)
{
- struct vring_desc desc;
- unsigned int i, head, found = 0;
- u16 last_avail_idx;
- __virtio16 avail_idx;
- __virtio16 ring_head;
- int ret, access;
-
- /* Check it isn't doing very strange things with descriptor numbers. */
- last_avail_idx = vq->last_avail_idx;
+ u16 last_avail_idx = vq->last_avail_idx;
+ __virtio16 avail_idx, ring_head;

if (vq->avail_idx == vq->last_avail_idx) {
if (unlikely(vhost_get_avail(vq, avail_idx, &vq->avail->idx))) {
vq_err(vq, "Failed to access avail idx at %p\n",
&vq->avail->idx);
- return -EFAULT;
+ goto err;
}
vq->avail_idx = vhost16_to_cpu(vq, avail_idx);

if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
vq_err(vq, "Guest moved used index from %u to %u",
last_avail_idx, vq->avail_idx);
- return -EFAULT;
+ goto err;
}

/* If there's nothing new since last we looked, return
@@ -2040,13 +2022,35 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
vq_err(vq, "Failed to read head: idx %d address %p\n",
last_avail_idx,
&vq->avail->ring[last_avail_idx % vq->num]);
- return -EFAULT;
+ goto err;
}

- head = vhost16_to_cpu(vq, ring_head);
+ return vhost16_to_cpu(vq, ring_head);
+err:
+ *err = -EFAULT;
+ return 0;
+}
+
+/* This looks in the virtqueue and for the first available buffer, and converts
+ * it to an iovec for convenient access. Since descriptors consist of some
+ * number of output then some number of input descriptors, it's actually two
+ * iovecs, but we pack them into one and note how many of each there were.
+ *
+ * This function returns the descriptor number found, or vq->num (which is
+ * never a valid descriptor number) if none was found. A negative code is
+ * returned on error. */
+int __vhost_get_vq_desc(struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_size,
+ unsigned int *out_num, unsigned int *in_num,
+ struct vhost_log *log, unsigned int *log_num,
+ __virtio16 head)
+{
+ struct vring_desc desc;
+ unsigned int i, found = 0;
+ int ret = 0, access;

/* If their number is silly, that's an error. */
- if (unlikely(head >= vq->num)) {
+ if (unlikely(head > vq->num)) {
vq_err(vq, "Guest says index %u > %u is available",
head, vq->num);
return -EINVAL;
@@ -2133,6 +2137,25 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
return head;
}
+EXPORT_SYMBOL_GPL(__vhost_get_vq_desc);
+
+int vhost_get_vq_desc(struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_size,
+ unsigned int *out_num, unsigned int *in_num,
+ struct vhost_log *log, unsigned int *log_num)
+{
+ int ret = 0;
+ unsigned int head = vhost_get_vq_head(vq, &ret);
+
+ if (ret)
+ return ret;
+
+ if (head == vq->num)
+ return head;
+
+ return __vhost_get_vq_desc(vq, iov, iov_size, out_num, in_num,
+ log, log_num, head);
+}
EXPORT_SYMBOL_GPL(vhost_get_vq_desc);

/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index d59a9cc..39ff897 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -191,6 +191,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
struct iovec iov[], unsigned int iov_count,
unsigned int *out_num, unsigned int *in_num,
struct vhost_log *log, unsigned int *log_num);
+int __vhost_get_vq_desc(struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_count,
+ unsigned int *out_num, unsigned int *in_num,
+ struct vhost_log *log, unsigned int *log_num,
+ __virtio16 ring_head);
void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);

int vhost_vq_init_access(struct vhost_virtqueue *);
--
2.7.4