[PATCH net-next RFC 08/10] packet: enable sendmsg zerocopy

[Willem de Bruijn]

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

Support MSG_ZEROCOPY on PF_PACKET transmission.

Signed-off-by: Willem de Bruijn <will...@google.com>
---
 net/packet/af_packet.c | 45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index b5afe53..8c5588b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2476,28 +2476,47 @@ out:
 
 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 = 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_zerocopy_sg_from_iovec(struct sk_buff *skb,
+                                        struct msghdr *msg, size_t size)
+{
+       if (zerocopy_sg_from_iter(skb, &msg->msg_iter))
+               return -EIO;
+       if (!skb_zerocopy_alloc(skb, size))
+               return -ENOMEM;
+
+       return 0;
+}
+
 static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 {
        struct sock *sk = sock->sk;
@@ -2515,6 +2534,7 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
        int hlen, tlen;
        int extra_len = 0;
        ssize_t n;
+       bool zerocopy = msg->msg_flags & MSG_ZEROCOPY;
 
        /*
         *      Get and verify the address.
@@ -2611,7 +2631,7 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
        tlen = dev->needed_tailroom;
        skb = packet_alloc_skb(sk, hlen + tlen, hlen, len,
                               __virtio16_to_cpu(false, vnet_hdr.hdr_len),
-                              msg->msg_flags & MSG_DONTWAIT, &err);
+                              msg->msg_flags, &err);
        if (skb == NULL)
                goto out_unlock;
 
@@ -2628,7 +2648,11 @@ 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);
+       if (zerocopy)
+               err = packet_zerocopy_sg_from_iovec(skb, msg, len);
+       else
+               err = skb_copy_datagram_from_iter(skb, offset, &msg->msg_iter,
+                                                 len);
        if (err)
                goto out_free;
 
@@ -2690,6 +2714,7 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
        return len;
 
 out_free:
+       sock_zerocopy_put_abort(skb_zcopy(skb));
        kfree_skb(skb);
 out_unlock:
        if (dev)
-- 
2.5.0.276.gf5e568e

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