inet: Remove explicit write references to sk/inet in ip_append_data

In order to allow simultaneous calls to ip_append_data on the same
socket, it must not modify any shared state in sk or inet (other
than those that are designed to allow that such as atomic counters).

This patch abstracts out write references to sk and inet_sk in
ip_append_data and its friends so that we may use the underlying
code in parallel.

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>

include/net/inet_sock.h

@@ -86,6 +86,19 @@ static inline struct inet_request_sock *inet_rsk(const struct request_sock *sk)
 	return (struct inet_request_sock *)sk;
 }
 
+struct inet_cork {
+	unsigned int		flags;
+	unsigned int		fragsize;
+	struct ip_options	*opt;
+	struct dst_entry	*dst;
+	int			length; /* Total length of all frames */
+	__be32			addr;
+	struct flowi		fl;
+	struct page		*page;
+	u32			off;
+	u8			tx_flags;
+};
+
 struct ip_mc_socklist;
 struct ipv6_pinfo;
 struct rtable;
@@ -143,15 +156,7 @@ struct inet_sock {
 	int			mc_index;
 	__be32			mc_addr;
 	struct ip_mc_socklist __rcu	*mc_list;
-	struct {
-		unsigned int		flags;
-		unsigned int		fragsize;
-		struct ip_options	*opt;
-		struct dst_entry	*dst;
-		int			length; /* Total length of all frames */
-		__be32			addr;
-		struct flowi		fl;
-	} cork;
+	struct inet_cork	cork;
 };
 
 #define IPCORK_OPT	1	/* ip-options has been held in ipcork.opt */