inet: Add ip_make_skb and ip_finish_skb

This patch adds the helper ip_make_skb which is like ip_append_data
and ip_push_pending_frames all rolled into one, except that it does
not send the skb produced.  The sending part is carried out by
ip_send_skb, which the transport protocol can call after it has
tweaked the skb.

It is meant to be called in cases where corking is not used should
have a one-to-one correspondence to sendmsg.

This patch also adds the helper ip_finish_skb which is meant to
be replace ip_push_pending_frames when corking is required.
Previously the protocol stack would peek at the socket write
queue and add its header to the first packet.  With ip_finish_skb,
the protocol stack can directly operate on the final skb instead,
just like the non-corking case with ip_make_skb.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 67 insertions, 14 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index 67fac78a186b..a4f631108c54 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -116,8 +116,24 @@ extern int		ip_append_data(struct sock *sk,
 extern int              ip_generic_getfrag(void *from, char *to, int offset, int len, int odd, struct sk_buff *skb);
 extern ssize_t          ip_append_page(struct sock *sk, struct page *page,
                                 int offset, size_t size, int flags);
+extern struct sk_buff  *__ip_make_skb(struct sock *sk,
+                                      struct sk_buff_head *queue,
+                                      struct inet_cork *cork);
+extern int              ip_send_skb(struct sk_buff *skb);
 extern int              ip_push_pending_frames(struct sock *sk);
 extern void             ip_flush_pending_frames(struct sock *sk);
+extern struct sk_buff  *ip_make_skb(struct sock *sk,
+                                    int getfrag(void *from, char *to, int offset, int len,
+                                                int odd, struct sk_buff *skb),
+                                    void *from, int length, int transhdrlen,
+                                    struct ipcm_cookie *ipc,
+                                    struct rtable **rtp,
+                                    unsigned int flags);
+
+static inline struct sk_buff *ip_finish_skb(struct sock *sk)
+{
+        return __ip_make_skb(sk, &sk->sk_write_queue, &inet_sk(sk)->cork);
+}
 
 /* datagram.c */
 extern int              ip4_datagram_connect(struct sock *sk, 
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 1dd5ecc9a27e..460308c35028 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1267,9 +1267,9 @@ static void ip_cork_release(struct inet_cork *cork)
  *      Combined all pending IP fragments on the socket as one IP datagram
  *      and push them out.
  */
-static int __ip_push_pending_frames(struct sock *sk,
-                                    struct sk_buff_head *queue,
-                                    struct inet_cork *cork)
+struct sk_buff *__ip_make_skb(struct sock *sk,
+                              struct sk_buff_head *queue,
+                              struct inet_cork *cork)
 {
         struct sk_buff *skb, *tmp_skb;
         struct sk_buff **tail_skb;
@@ -1280,7 +1280,6 @@ static int __ip_push_pending_frames(struct sock *sk,
         struct iphdr *iph;
         __be16 df = 0;
         __u8 ttl;
-        int err = 0;
 
         if ((skb = __skb_dequeue(queue)) == NULL)
                 goto out;
@@ -1351,28 +1350,37 @@ static int __ip_push_pending_frames(struct sock *sk,
                 icmp_out_count(net, ((struct icmphdr *)
                         skb_transport_header(skb))->type);
 
-        /* Netfilter gets whole the not fragmented skb. */
+        ip_cork_release(cork);
+out:
+        return skb;
+}
+
+int ip_send_skb(struct sk_buff *skb)
+{
+        struct net *net = sock_net(skb->sk);
+        int err;
+
         err = ip_local_out(skb);
         if (err) {
                 if (err > 0)
                         err = net_xmit_errno(err);
                 if (err)
-                        goto error;
+                        IP_INC_STATS(net, IPSTATS_MIB_OUTDISCARDS);
         }
 
-out:
-        ip_cork_release(cork);
         return err;
-
-error:
-        IP_INC_STATS(net, IPSTATS_MIB_OUTDISCARDS);
-        goto out;
 }
 
 int ip_push_pending_frames(struct sock *sk)
 {
-        return __ip_push_pending_frames(sk, &sk->sk_write_queue,
-                                        &inet_sk(sk)->cork);
+        struct sk_buff *skb;
+
+        skb = ip_finish_skb(sk);
+        if (!skb)
+                return 0;
+
+        /* Netfilter gets whole the not fragmented skb. */
+        return ip_send_skb(skb);
 }
 
 /*
@@ -1395,6 +1403,35 @@ void ip_flush_pending_frames(struct sock *sk)
         __ip_flush_pending_frames(sk, &sk->sk_write_queue, &inet_sk(sk)->cork);
 }
 
+struct sk_buff *ip_make_skb(struct sock *sk,
+                            int getfrag(void *from, char *to, int offset,
+                                        int len, int odd, struct sk_buff *skb),
+                            void *from, int length, int transhdrlen,
+                            struct ipcm_cookie *ipc, struct rtable **rtp,
+                            unsigned int flags)
+{
+        struct inet_cork cork = {};
+        struct sk_buff_head queue;
+        int err;
+
+        if (flags & MSG_PROBE)
+                return NULL;
+
+        __skb_queue_head_init(&queue);
+
+        err = ip_setup_cork(sk, &cork, ipc, rtp);
+        if (err)
+                return ERR_PTR(err);
+
+        err = __ip_append_data(sk, &queue, &cork, getfrag,
+                               from, length, transhdrlen, flags);
+        if (err) {
+                __ip_flush_pending_frames(sk, &queue, &cork);
+                return ERR_PTR(err);
+        }
+
+        return __ip_make_skb(sk, &queue, &cork);
+}
 
 /*
  *      Fetch data from kernel space and fill in checksum if needed.