[PATCH net-next v2 12/13] packet: enable MSG_ZEROCOPY

[Willem de Bruijn]

From: Willem de Bruijn <will...@google.com>

Support MSG_ZEROCOPY on PF_PACKET transmission.

Tested:

  msg_zerocopy.sh 4 packet:

  without zerocopy
    tx=121543 (7588 MB) txc=0 zc=n
    rx=121543 (7584 MB)

  with zerocopy
    tx=338252 (21119 MB) txc=338252 zc=y
    rx=338252 (21108 MB)

  msg_zerocopy.sh 4 packet_dgram:

  without zerocopy
    tx=122699 (7659 MB) txc=0 zc=n
    rx=122699 (7656 MB)

  with zerocopy
    tx=340390 (21248 MB) txc=340390 zc=y
    rx=340390 (21241 MB)

Signed-off-by: Willem de Bruijn <will...@google.com>
---
 net/packet/af_packet.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index f9349a495caf..a04791fd81f2 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2795,30 +2795,39 @@ static int tpacket_snd(struct packet_sock *po, struct 
msghdr *msg)
 
 static struct sk_buff *packet_alloc_skb(struct sock *sk, size_t prepad,
                                        size_t reserve, size_t len,
-                                       size_t linear, int noblock,
+                                       size_t linear, int flags,
                                        int *err)
 {
        struct sk_buff *skb;
+       size_t data_len;
 
-       /* Under a page?  Don't bother with paged skb. */
-       if (prepad + len < PAGE_SIZE || !linear)
-               linear = len;
+       if (flags & MSG_ZEROCOPY) {
+               /* Minimize linear, but respect header lower bound */
+               linear = reserve + min(len, max_t(size_t, linear, MAX_HEADER));
+               data_len = 0;
+       } else {
+               /* Under a page? Don't bother with paged skb. */
+               if (prepad + len < PAGE_SIZE || !linear)
+                       linear = len;
+               data_len = len - linear;
+       }
 
-       skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
-                                  err, 0);
+       skb = sock_alloc_send_pskb(sk, prepad + linear, data_len,
+                                  flags & MSG_DONTWAIT, err, 0);
        if (!skb)
                return NULL;
 
        skb_reserve(skb, reserve);
        skb_put(skb, linear);
-       skb->data_len = len - linear;
-       skb->len += len - linear;
+       skb->data_len = data_len;
+       skb->len += data_len;
 
        return skb;
 }
 
 static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 {
+       struct iov_iter *from = &msg->msg_iter;
        struct sock *sk = sock->sk;
        DECLARE_SOCKADDR(struct sockaddr_ll *, saddr, msg->msg_name);
        struct sk_buff *skb;
@@ -2894,7 +2903,7 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
        linear = __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len);
        linear = max(linear, min_t(int, len, dev->hard_header_len));
        skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, linear,
-                              msg->msg_flags & MSG_DONTWAIT, &err);
+                              msg->msg_flags, &err);
        if (skb == NULL)
                goto out_unlock;
 
@@ -2908,10 +2917,16 @@ static int packet_snd(struct socket *sock, struct 
msghdr *msg, size_t len)
        }
 
        /* Returns -EFAULT on error */
-       err = skb_copy_datagram_from_iter(skb, offset, &msg->msg_iter, len);
+       err = skb_copy_datagram_from_iter(skb, offset, from, skb->len - offset);
        if (err)
                goto out_free;
 
+       if (msg->msg_flags & MSG_ZEROCOPY && len) {
+               err = skb_zerocopy_iter_alloc(skb, msg, iov_iter_count(from));
+               if (err)
+                       goto out_free;
+       }
+
        if (sock->type == SOCK_RAW &&
            !dev_validate_header(dev, skb->data, len)) {
                err = -EINVAL;
@@ -2954,6 +2969,7 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
        return len;
 
 out_free:
+       skb_zcopy_abort(skb);
        kfree_skb(skb);
 out_unlock:
        if (dev)
-- 
2.13.1.611.g7e3b11ae1-goog