On Wed, 2015-05-20 at 17:35 +0200, Hannes Frederic Sowa wrote:
> This patch implements sendpage support for AF_UNIX SOCK_STREAM
> sockets. This is also required for a complete splice implementation.
>
> The implementation is a bit tricky because we append to already existing
> skbs and so have to hold unix_sk->readlock to protect the reading side
> from dropping the tail of the sk_receive_queue.
>
> Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org>
> ---
> net/unix/af_unix.c | 105
> ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 104 insertions(+), 1 deletion(-)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 941b3d2..9bb880a 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -518,6 +518,8 @@ static int unix_ioctl(struct socket *, unsigned int,
> unsigned long);
> static int unix_shutdown(struct socket *, int);
> static int unix_stream_sendmsg(struct socket *, struct msghdr *, size_t);
> static int unix_stream_recvmsg(struct socket *, struct msghdr *, size_t,
> int);
> +static ssize_t unix_stream_sendpage(struct socket *, struct page *, int
> offset,
> + size_t size, int flags);
> static int unix_dgram_sendmsg(struct socket *, struct msghdr *, size_t);
> static int unix_dgram_recvmsg(struct socket *, struct msghdr *, size_t, int);
> static int unix_dgram_connect(struct socket *, struct sockaddr *,
> @@ -558,7 +560,7 @@ static const struct proto_ops unix_stream_ops = {
> .sendmsg = unix_stream_sendmsg,
> .recvmsg = unix_stream_recvmsg,
> .mmap = sock_no_mmap,
> - .sendpage = sock_no_sendpage,
> + .sendpage = unix_stream_sendpage,
> .set_peek_off = unix_set_peek_off,
> };
>
> @@ -1720,6 +1722,107 @@ out_err:
> return sent ? : err;
> }
>
> +static ssize_t unix_stream_sendpage(struct socket *socket, struct page *page,
> + int offset, size_t size, int flags)
> +{
> + int err;
> + bool send_sigpipe;
> + struct sock *sk, *other;
> + struct sk_buff *skb, *newskb, *tail;
> +
> + err = 0;
> + tail = NULL;
> + newskb = NULL;
> + sk = socket->sk;
> + send_sigpipe = true;
> +
> + if (flags & MSG_OOB)
> + return -EOPNOTSUPP;
> +
> + other = unix_peer(sk);
> + if (!other || sk->sk_state != TCP_ESTABLISHED)
> + return -ENOTCONN;
> +
> + if (false) {
> +alloc_skb:
> + unix_state_unlock(other);
> + mutex_unlock(&unix_sk(other)->readlock);
> + newskb = sock_alloc_send_pskb(sk, 0, 0, flags & MSG_DONTWAIT,
> + &err, 0);
> + if (!newskb)
> + return err;
> + }
> +
> + /* we must acquire readlock as we modify already present
> + * skbs in the sk_receive_queue and mess with skb->len
> + */
> + err = mutex_lock_interruptible(&unix_sk(other)->readlock);
> + if (err) {
> + err = flags & MSG_DONTWAIT ? -EAGAIN : -ERESTARTSYS;
> + send_sigpipe = false;
> + goto err;
> + }
> +
> + if (sk->sk_shutdown & SEND_SHUTDOWN) {
> + err = -EPIPE;
> + goto err_unlock;
> + }
> +
> + unix_state_lock(other);
> +
> + if (sock_flag(other, SOCK_DEAD) ||
> + other->sk_shutdown & RCV_SHUTDOWN) {
> + err = -EPIPE;
> + goto err_state_unlock;
> + }
> +
> + skb = skb_peek_tail(&other->sk_receive_queue);
> + if (tail && tail == skb) {
> + skb = newskb;
> + } else if (!skb) {
> + if (newskb)
> + skb = newskb;
> + else
> + goto alloc_skb;
> + } else if (newskb) {
> + /* this is fast path, we don't necessarily need to
> + * call to kfree_skb even though with newskb == NULL
> + * this - does no harm
> + */
> + consume_skb(newskb);
> + }
> +
> + if (skb_append_pagefrags(skb, page, offset, size)) {
> + tail = skb;
> + goto alloc_skb;
> + }
> +
> + skb->len += size;
> + skb->data_len += size;
> + skb->truesize += size;
> + atomic_add(size, &sk->sk_wmem_alloc);
> +
> + if (newskb)
> + skb_queue_tail(&other->sk_receive_queue, newskb);
Are you sure we need the skb_queue_tail() here (taking spinlock) ?
This would tell us there might be a possible race.
A comment would be nice eventually.
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