Subject: Re: [PATCHv7] add mergeable buffers support to vhost_net

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 29 Apr 2010 16:45:15 +0300

On Wed, Apr 28, 2010 at 01:57:12PM -0700, David L Stevens wrote:
> This patch adds mergeable receive buffer support to vhost_net.
> 
> Signed-off-by: David L Stevens <[email-masked]>

I have applied this, thanks very much!
I have also applied some tweaks on top,
please take a look.

Thanks,
MSt

commit 2809e94f5f26d89dc5232aaec753ffda95c4d95e
Author: Michael S. Tsirkin <[email-masked]>
Date:   Thu Apr 29 16:18:08 2010 +0300

    vhost-net: minor tweaks in mergeable buffer code
    
    Applies the following tweaks on top of mergeable buffers patch:
    1. vhost_get_desc_n assumes that all desriptors are 'in' only.
       It's also unlikely to be useful for any vhost frontend
       besides vhost_net, so just move it to net.c, and rename
       get_rx_bufs for brevity.
    
    2. for rx, we called iov_length within vhost_get_desc_n
       (now get_rx_bufs) already, so we don't
       need an extra call to iov_length to avoid overflow anymore.
       Accordingly, copy_iovec_hdr can return void now.
    
    3. for rx, do some further code tweaks:
       do not assign len = err as we check that err == len
       handle data length in a way similar to how we handle
       header length: datalen -> sock_len, len -> vhost_len.
       add sock_hlen as a local variable, for symmetry with vhost_hlen.

    4. add some likely/unlikely annotations
    
    Signed-off-by: Michael S. Tsirkin <[email-masked]>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d61d945..85519b4 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -74,9 +74,9 @@ static int move_iovec_hdr(struct iovec *from, struct iovec *to,
 	}
 	return seg;
 }
-/* Copy iovec entries for len bytes from iovec. Return segments used. */
-static int copy_iovec_hdr(const struct iovec *from, struct iovec *to,
-			  size_t len, int iovcount)
+/* Copy iovec entries for len bytes from iovec. */
+static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
+			   size_t len, int iovcount)
 {
 	int seg = 0;
 	size_t size;
@@ -89,7 +89,6 @@ static int copy_iovec_hdr(const struct iovec *from, struct iovec *to,
 		++to;
 		++seg;
 	}
-	return seg;
 }
 
 /* Caller must have TX VQ lock */
@@ -204,7 +203,7 @@ static void handle_tx(struct vhost_net *net)
 	unuse_mm(net->dev.mm);
 }
 
-static int vhost_head_len(struct vhost_virtqueue *vq, struct sock *sk)
+static int peek_head_len(struct vhost_virtqueue *vq, struct sock *sk)
 {
 	struct sk_buff *head;
 	int len = 0;
@@ -212,17 +211,70 @@ static int vhost_head_len(struct vhost_virtqueue *vq, struct sock *sk)
 	lock_sock(sk);
 	head = skb_peek(&sk->sk_receive_queue);
 	if (head)
-		len = head->len + vq->sock_hlen;
+		len = head->len;
 	release_sock(sk);
 	return len;
 }
 
+/* This is a multi-buffer version of vhost_get_desc, that works if
+ *	vq has read descriptors only.
+ * @vq		- the relevant virtqueue
+ * @datalen	- data length we'll be reading
+ * @iovcount	- returned count of io vectors we fill
+ * @log		- vhost log
+ * @log_num	- log offset
+ *	returns number of buffer heads allocated, negative on error
+ */
+static int get_rx_bufs(struct vhost_virtqueue *vq,
+		       struct vring_used_elem *heads,
+		       int datalen,
+		       unsigned *iovcount,
+		       struct vhost_log *log,
+		       unsigned *log_num)
+{
+	unsigned int out, in;
+	int seg = 0;
+	int headcount = 0;
+	unsigned d;
+	int r;
+
+	while (datalen > 0) {
+		if (unlikely(headcount >= VHOST_NET_MAX_SG)) {
+			r = -ENOBUFS;
+			goto err;
+		}
+		d = vhost_get_desc(vq->dev, vq, vq->iov + seg,
+				   ARRAY_SIZE(vq->iov) - seg, &out,
+				   &in, log, log_num);
+		if (d == vq->num) {
+			r = 0;
+			goto err;
+		}
+		if (unlikely(out || in <= 0)) {
+			vq_err(vq, "unexpected descriptor format for RX: "
+				"out %d, in %d\n", out, in);
+			r = -EINVAL;
+			goto err;
+		}
+		heads[headcount].id = d;
+		heads[headcount].len = iov_length(vq->iov + seg, in);
+		datalen -= heads[headcount].len;
+		++headcount;
+		seg += in;
+	}
+	*iovcount = seg;
+	return headcount;
+err:
+	vhost_discard_desc(vq, headcount);
+	return r;
+}
+
 /* Expects to be always run from workqueue - which acts as
  * read-size critical section for our kind of RCU. */
 static void handle_rx(struct vhost_net *net)
 {
 	struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
-	unsigned in, log, s;
+	unsigned uninitialized_var(in), log;
 	struct vhost_log *vq_log;
 	struct msghdr msg = {
 		.msg_name = NULL,
@@ -238,9 +290,10 @@ static void handle_rx(struct vhost_net *net)
 		.hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
 	};
 
-	size_t len, total_len = 0;
-	int err, headcount, datalen;
-	size_t vhost_hlen;
+	size_t total_len = 0;
+	int err, headcount;
+	size_t vhost_hlen, sock_hlen;
+	size_t vhost_len, sock_len;
 	struct socket *sock = rcu_dereference(vq->private_data);
 	if (!sock || skb_queue_empty(&sock->sk->sk_receive_queue))
 		return;
@@ -249,14 +302,16 @@ static void handle_rx(struct vhost_net *net)
 	mutex_lock(&vq->mutex);
 	vhost_disable_notify(vq);
 	vhost_hlen = vq->vhost_hlen;
+	sock_hlen = vq->sock_hlen;
 
 	vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
 		vq->log : NULL;
 
-	while ((datalen = vhost_head_len(vq, sock->sk))) {
-		headcount = vhost_get_desc_n(vq, vq->heads,
-					     datalen + vhost_hlen,
-					     &in, vq_log, &log);
+	while ((sock_len = peek_head_len(vq, sock->sk))) {
+		sock_len += sock_hlen;
+		vhost_len = sock_len + vhost_hlen;
+		headcount = get_rx_bufs(vq, vq->heads, vhost_len,
+					&in, vq_log, &log);
 		if (headcount < 0)
 			break;
 		/* OK, now we need to know about added descriptors. */
@@ -272,34 +327,25 @@ static void handle_rx(struct vhost_net *net)
 			break;
 		}
 		/* We don't need to be notified again. */
-		if (vhost_hlen)
+		if (unlikely((vhost_hlen)))
 			/* Skip header. TODO: support TSO. */
-			s = move_iovec_hdr(vq->iov, vq->hdr, vhost_hlen, in);
+			move_iovec_hdr(vq->iov, vq->hdr, vhost_hlen, in);
 		else
-			s = copy_iovec_hdr(vq->iov, vq->hdr, vq->sock_hlen, in);
+			copy_iovec_hdr(vq->iov, vq->hdr, sock_hlen, in);
 		msg.msg_iovlen = in;
-		len = iov_length(vq->iov, in);
-		/* Sanity check */
-		if (!len) {
-			vq_err(vq, "Unexpected header len for RX: "
-			       "%zd expected %zd\n",
-			       iov_length(vq->hdr, s), vhost_hlen);
-			break;
-		}
 		err = sock->ops->recvmsg(NULL, sock, &msg,
-					 len, MSG_DONTWAIT | MSG_TRUNC);
+					 sock_len, MSG_DONTWAIT | MSG_TRUNC);
 		/* TODO: Check specific error and bomb out unless EAGAIN? */
 		if (err < 0) {
 			vhost_discard_desc(vq, headcount);
 			break;
 		}
-		if (err != datalen) {
+		if (err != sock_len) {
 			pr_err("Discarded rx packet: "
-			       " len %d, expected %zd\n", err, datalen);
+			       " len %d, expected %zd\n", err, sock_len);
 			vhost_discard_desc(vq, headcount);
 			continue;
 		}
-		len = err;
 		if (vhost_hlen &&
 		    memcpy_toiovecend(vq->hdr, (unsigned char *)&hdr, 0,
 				      vhost_hlen)) {
@@ -311,17 +357,16 @@ static void handle_rx(struct vhost_net *net)
 		if (vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF) &&
 		    memcpy_toiovecend(vq->hdr, (unsigned char *)&headcount,
 				      offsetof(typeof(hdr), num_buffers),
-				      sizeof(hdr.num_buffers))) {
+				      sizeof hdr.num_buffers)) {
 			vq_err(vq, "Failed num_buffers write");
 			vhost_discard_desc(vq, headcount);
 			break;
 		}
-		len += vhost_hlen;
 		vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
 					    headcount);
 		if (unlikely(vq_log))
-			vhost_log_write(vq, vq_log, log, len);
-		total_len += len;
+			vhost_log_write(vq, vq_log, log, vhost_len);
+		total_len += vhost_len;
 		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
 			vhost_poll_queue(&vq->poll);
 			break;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8ef5e3f..4b49991 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -862,53 +862,6 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 	return 0;
 }
 
-/* This is a multi-buffer version of vhost_get_desc
- * @vq		- the relevant virtqueue
- * datalen	- data length we'll be reading
- * @iovcount	- returned count of io vectors we fill
- * @log		- vhost log
- * @log_num	- log offset
- *	returns number of buffer heads allocated, negative on error
- */
-int vhost_get_desc_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
-		     int datalen, unsigned *iovcount, struct vhost_log *log,
-		     unsigned int *log_num)
-{
-	unsigned int out, in;
-	int seg = 0;
-	int headcount = 0;
-	int r;
-
-	while (datalen > 0) {
-		if (headcount >= VHOST_NET_MAX_SG) {
-			r = -ENOBUFS;
-			goto err;
-		}
-		heads[headcount].id = vhost_get_desc(vq->dev, vq, vq->iov + seg,
-					      ARRAY_SIZE(vq->iov) - seg, &out,
-					      &in, log, log_num);
-		if (heads[headcount].id == vq->num) {
-			r = 0;
-			goto err;
-		}
-		if (out || in <= 0) {
-			vq_err(vq, "unexpected descriptor format for RX: "
-				"out %d, in %d\n", out, in);
-			r = -EINVAL;
-			goto err;
-		}
-		heads[headcount].len = iov_length(vq->iov + seg, in);
-		datalen -= heads[headcount].len;
-		++headcount;
-		seg += in;
-	}
-	*iovcount = seg;
-	return headcount;
-err:
-	vhost_discard_desc(vq, headcount);
-	return r;
-}
-
 /* 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
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 08d740a..4c9809e 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -122,9 +122,6 @@ long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
 int vhost_vq_access_ok(struct vhost_virtqueue *vq);
 int vhost_log_access_ok(struct vhost_dev *);
 
-int vhost_get_desc_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
-		     int datalen, unsigned int *iovcount, struct vhost_log *log,
-		     unsigned int *log_num);
 unsigned vhost_get_desc(struct vhost_dev *, struct vhost_virtqueue *,
 			   struct iovec iov[], unsigned int iov_count,
 			   unsigned int *out_num, unsigned int *in_num,

-- 
MST