net: introduce proto_ports_offset()

Introduce proto_ports_offset() for getting the position of the ports or
SPI in the message of a protocol.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/linux/in.h b/include/linux/in.h
index 41d88a4689af..beeb6dee2b49 100644
--- a/include/linux/in.h
+++ b/include/linux/in.h
@@ -250,6 +250,25 @@ struct sockaddr_in {
 
 #ifdef __KERNEL__
 
+#include <linux/errno.h>
+
+static inline int proto_ports_offset(int proto)
+{
+        switch (proto) {
+        case IPPROTO_TCP:
+        case IPPROTO_UDP:
+        case IPPROTO_DCCP:
+        case IPPROTO_ESP:       /* SPI */
+        case IPPROTO_SCTP:
+        case IPPROTO_UDPLITE:
+                return 0;
+        case IPPROTO_AH:        /* SPI */
+                return 4;
+        default:
+                return -EINVAL;
+        }
+}
+
 static inline bool ipv4_is_loopback(__be32 addr)
 {
         return (addr & htonl(0xff000000)) == htonl(0x7f000000);