[PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()

Jason Wang
2017-09-22T08:02:33Z

This patch introduces a helper which just increase the used idx. This
will be used in pair with vhost_prefetch_desc_indices() by batching
code.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/vhost.c | 33 +++++++++++++++++++++++++++++++++
drivers/vhost/vhost.h | 1 +
2 files changed, 34 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8424166d..6532cda 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2178,6 +2178,39 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
}
EXPORT_SYMBOL_GPL(vhost_add_used);

+int vhost_add_used_idx(struct vhost_virtqueue *vq, int n)
+{
+ u16 old, new;
+
+ old = vq->last_used_idx;
+ new = (vq->last_used_idx += n);
+ /* If the driver never bothers to signal in a very long while,
+ * used index might wrap around. If that happens, invalidate
+ * signalled_used index we stored. TODO: make sure driver
+ * signals at least once in 2^16 and remove this.
+ */
+ if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old)))
+ vq->signalled_used_valid = false;
+
+ /* Make sure buffer is written before we update index. */
+ smp_wmb();
+ if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx),
+ &vq->used->idx)) {
+ vq_err(vq, "Failed to increment used idx");
+ return -EFAULT;
+ }
+ if (unlikely(vq->log_used)) {
+ /* Log used index update. */
+ log_write(vq->log_base,
+ vq->log_addr + offsetof(struct vring_used, idx),
+ sizeof(vq->used->idx));
+ if (vq->log_ctx)
+ eventfd_signal(vq->log_ctx, 1);
+ }
+ return 0;
+}
+EXPORT_SYMBOL_GPL(vhost_add_used_idx);
+
static int __vhost_add_used_n(struct vhost_virtqueue *vq,
struct vring_used_elem *heads,
unsigned count)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 16c2cb6..5dd6c05 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -199,6 +199,7 @@ int __vhost_get_vq_desc(struct vhost_virtqueue *vq,
void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);

int vhost_vq_init_access(struct vhost_virtqueue *);
+int vhost_add_used_idx(struct vhost_virtqueue *vq, int n);
int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
unsigned count);
--
2.7.4