Linux Virtualization - Feb 2015 - [PATCH v3 16/18] vhost: don't bother with copying iovec in handle_tx()

From: Al Viro <viro at zeniv.linux.org.uk>

just advance the msg.msg_iter and be done with that.

Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: kvm at vger.kernel.org
Cc: virtualization at lists.linux-foundation.org
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
---
 drivers/vhost/net.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 6906f76..d86cc9b 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -336,7 +336,7 @@ static void handle_tx(struct vhost_net *net)
 {
 	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
 	struct vhost_virtqueue *vq = &nvq->vq;
-	unsigned out, in, s;
+	unsigned out, in;
 	int head;
 	struct msghdr msg = {
 		.msg_name = NULL,
@@ -395,16 +395,17 @@ static void handle_tx(struct vhost_net *net)
 			break;
 		}
 		/* Skip header. TODO: support TSO. */
-		s = move_iovec_hdr(vq->iov, nvq->hdr, hdr_size, out);
 		len = iov_length(vq->iov, out);
 		iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
+		iov_iter_advance(&msg.msg_iter, hdr_size);
 		/* Sanity check */
-		if (!len) {
+		if (!iov_iter_count(&msg.msg_iter)) {
 			vq_err(vq, "Unexpected header len for TX: "
 			       "%zd expected %zd\n",
-			       iov_length(nvq->hdr, s), hdr_size);
+			       len, hdr_size);
 			break;
 		}
+		len = iov_iter_count(&msg.msg_iter);
 
 		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
 				   && (nvq->upend_idx + 1) % UIO_MAXIOV !-- 
2.1.4

On Wed, Feb 04, 2015 at 06:40:07AM +0000, Al Viro wrote:
> From: Al Viro <viro at zeniv.linux.org.uk>
> 
> just advance the msg.msg_iter and be done with that.
> 
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: kvm at vger.kernel.org
> Cc: virtualization at lists.linux-foundation.org
> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/vhost/net.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 6906f76..d86cc9b 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -336,7 +336,7 @@ static void handle_tx(struct vhost_net *net)
>  {
>  	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>  	struct vhost_virtqueue *vq = &nvq->vq;
> -	unsigned out, in, s;
> +	unsigned out, in;
>  	int head;
>  	struct msghdr msg = {
>  		.msg_name = NULL,
> @@ -395,16 +395,17 @@ static void handle_tx(struct vhost_net *net)
>  			break;
>  		}
>  		/* Skip header. TODO: support TSO. */
> -		s = move_iovec_hdr(vq->iov, nvq->hdr, hdr_size, out);
>  		len = iov_length(vq->iov, out);
>  		iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
> +		iov_iter_advance(&msg.msg_iter, hdr_size);
>  		/* Sanity check */
> -		if (!len) {
> +		if (!iov_iter_count(&msg.msg_iter)) {
>  			vq_err(vq, "Unexpected header len for TX: "
>  			       "%zd expected %zd\n",
> -			       iov_length(nvq->hdr, s), hdr_size);
> +			       len, hdr_size);
>  			break;
>  		}
> +		len = iov_iter_count(&msg.msg_iter);
>  
>  		zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
>  				   && (nvq->upend_idx + 1) % UIO_MAXIOV !> -- 
> 2.1.4