[PATCH RFC 07/13] vhost: format-independent API for used buffers

["Michael S. Tsirkin" <mst@redhat.com>]

Add a new API that doesn't assume used ring, heads, etc.
For now, we keep the old APIs around to make it easier
to convert drivers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/vhost/vhost.c | 52 ++++++++++++++++++++++++++++++++++---------
 drivers/vhost/vhost.h | 17 +++++++++++++-
 2 files changed, 58 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b4a6e44d56a8..be822f0c9428 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2292,13 +2292,12 @@ static int fetch_descs(struct vhost_virtqueue *vq)
  * 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)
+ * This function returns a value > 0 if a descriptor was found, or 0 if none were found.
+ * A negative code is returned on error. */
+int vhost_get_avail_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf,
+			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 = fetch_descs(vq);
 	int i;
@@ -2311,6 +2310,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 	*out_num = *in_num = 0;
 	if (unlikely(log))
 		*log_num = 0;
+	buf->in_len = buf->out_len = 0;
+	buf->descs = 0;
 
 	for (i = vq->first_desc; i < vq->ndescs; ++i) {
 		unsigned iov_count = *in_num + *out_num;
@@ -2340,6 +2341,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 			/* If this is an input descriptor,
 			 * increment that count. */
 			*in_num += ret;
+			buf->in_len += desc->len;
 			if (unlikely(log && ret)) {
 				log[*log_num].addr = desc->addr;
 				log[*log_num].len = desc->len;
@@ -2355,9 +2357,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 				goto err;
 			}
 			*out_num += ret;
+			buf->out_len += desc->len;
 		}
 
-		ret = desc->id;
+		buf->id = desc->id;
+		++buf->descs;
 
 		if (!(desc->flags & VRING_DESC_F_NEXT))
 			break;
@@ -2365,7 +2369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 
 	vq->first_desc = i + 1;
 
-	return ret;
+	return 1;
 
 err:
 	for (i = vq->first_desc; i < vq->ndescs; ++i)
@@ -2375,7 +2379,15 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
+EXPORT_SYMBOL_GPL(vhost_get_avail_buf);
+
+/* Reverse the effect of vhost_get_avail_buf. Useful for error handling. */
+void vhost_discard_avail_bufs(struct vhost_virtqueue *vq,
+			      struct vhost_buf *buf, unsigned count)
+{
+	vhost_discard_vq_desc(vq, count);
+}
+EXPORT_SYMBOL_GPL(vhost_discard_avail_bufs);
 
 static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 			    struct vring_used_elem *heads,
@@ -2459,6 +2471,26 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
 }
 EXPORT_SYMBOL_GPL(vhost_add_used);
 
+int vhost_put_used_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf)
+{
+	return vhost_add_used(vq, buf->id, buf->in_len);
+}
+EXPORT_SYMBOL_GPL(vhost_put_used_buf);
+
+int vhost_put_used_n_bufs(struct vhost_virtqueue *vq,
+			  struct vhost_buf *bufs, unsigned count)
+{
+	unsigned i;
+
+	for (i = 0; i < count; ++i) {
+		vq->heads[i].id = cpu_to_vhost32(vq, bufs[i].id);
+		vq->heads[i].len = cpu_to_vhost32(vq, bufs[i].in_len);
+	}
+
+	return vhost_add_used_n(vq, vq->heads, count);
+}
+EXPORT_SYMBOL_GPL(vhost_put_used_n_bufs);
+
 static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
 	__u16 old, new;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a67bda9792ec..6c10e99ff334 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -67,6 +67,13 @@ struct vhost_desc {
 	u16 id;
 };
 
+struct vhost_buf {
+	u32 out_len;
+	u32 in_len;
+	u16 descs;
+	u16 id;
+};
+
 /* The virtqueue structure describes a queue attached to a device. */
 struct vhost_virtqueue {
 	struct vhost_dev *dev;
@@ -193,7 +200,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
 		      unsigned int *out_num, unsigned int *in_num,
 		      struct vhost_log *log, unsigned int *log_num);
 void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
-
+int vhost_get_avail_buf(struct vhost_virtqueue *, struct vhost_buf *buf,
+			struct iovec iov[], unsigned int iov_count,
+			unsigned int *out_num, unsigned int *in_num,
+			struct vhost_log *log, unsigned int *log_num);
+void vhost_discard_avail_bufs(struct vhost_virtqueue *,
+			      struct vhost_buf *, unsigned count);
 int vhost_vq_init_access(struct vhost_virtqueue *);
 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,
@@ -202,6 +214,9 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
 			       unsigned int id, int len);
 void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
 			       struct vring_used_elem *heads, unsigned count);
+int vhost_put_used_buf(struct vhost_virtqueue *, struct vhost_buf *buf);
+int vhost_put_used_n_bufs(struct vhost_virtqueue *,
+			  struct vhost_buf *bufs, unsigned count);
 void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
 void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
-- 
MST