Subject: Re: [PATCH V2 net-next 6/7] tap: support receiving skb from msg_control

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 30 Mar 2017 18:03:05 +0300

On Thu, Mar 30, 2017 at 03:22:29PM +0800, Jason Wang wrote:
> This patch makes tap_recvmsg() can receive from skb from its caller
> through msg_control. Vhost_net will be the first user.
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/tap.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index abdaf86..07d9174 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -824,15 +824,17 @@ static ssize_t tap_put_user(struct tap_queue *q,
>  
>  static ssize_t tap_do_read(struct tap_queue *q,
>  			   struct iov_iter *to,
> -			   int noblock)
> +			   int noblock, struct sk_buff *skb)
>  {
>  	DEFINE_WAIT(wait);
> -	struct sk_buff *skb;
>  	ssize_t ret = 0;
>  
>  	if (!iov_iter_count(to))
>  		return 0;
>  
> +	if (skb)
> +		goto done;
> +
>  	while (1) {
>  		if (!noblock)
>  			prepare_to_wait(sk_sleep(&q->sk), &wait,
> @@ -856,6 +858,7 @@ static ssize_t tap_do_read(struct tap_queue *q,
>  	if (!noblock)
>  		finish_wait(sk_sleep(&q->sk), &wait);
>  
> +done:

Please just use an if {} block here. goto on error is ok,
but we are far from done here and goto done is misleading.

>  	if (skb) {
>  		ret = tap_put_user(q, skb, to);
>  		if (unlikely(ret < 0))
> @@ -872,7 +875,7 @@ static ssize_t tap_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	struct tap_queue *q = file->private_data;
>  	ssize_t len = iov_iter_count(to), ret;
>  
> -	ret = tap_do_read(q, to, file->f_flags & O_NONBLOCK);
> +	ret = tap_do_read(q, to, file->f_flags & O_NONBLOCK, NULL);
>  	ret = min_t(ssize_t, ret, len);
>  	if (ret > 0)
>  		iocb->ki_pos = ret;
> @@ -1155,7 +1158,8 @@ static int tap_recvmsg(struct socket *sock, struct msghdr *m,
>  	int ret;
>  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
>  		return -EINVAL;
> -	ret = tap_do_read(q, &m->msg_iter, flags & MSG_DONTWAIT);
> +	ret = tap_do_read(q, &m->msg_iter, flags & MSG_DONTWAIT,
> +			  m->msg_control);
>  	if (ret > total_len) {
>  		m->msg_flags |= MSG_TRUNC;
>  		ret = flags & MSG_TRUNC ? ret : total_len;
> -- 
> 2.7.4