tc: add ACT_CSUM action support (csum)

tc: add ACT_CSUM action support (csum)

Add the iproute2 support for the ACT_CSUM action. Can be used as following, certainly in conjunction with the ACT_PEDIT action (pedit):

# In order to DNAT (stateless) IPv4 packet from 192.168.1.100 to # 0x12345678 (18.52.86.120), and update the IPv4 header checksum and # the UDP checksum (the last one, only if the packet is UDP). tc filter add eth0 prio 1 protocol ip parent ffff: \
u32 match ip src 192.168.1.100/32 flowid :1 \
action pedit munge offset 16 u32 set 0x12345678 \
pipe csum ip and udp

# In order to alter destination address of IPv6 TCP packets from fc00::1 # and correct the TCP checksum (nothing happened? except maybe for # checksums in the TCP payload ...).
tc filter add eth0 prio 1 protocol ipv6 parent ffff: \
u32 match ip6 src fc00::1/128 match ip6 protocol 0x06 0xff flowid :1 \
action pedit munge offset 24 u32 set 0x12345678 \
pipe csum tcp

Version 2 changes:
- correction in print_csum() (bad statistics print)

---
 include/linux/tc_act/tc_csum.h |   32 +++++
 tc/Makefile                    |    1 +
 tc/m_csum.c                    |  246 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 279 insertions(+), 0 deletions(-)
 create mode 100644 include/linux/tc_act/tc_csum.h
 create mode 100644 tc/m_csum.c

new file mode 100644
index 0000000..a047c49
@@ -0,0 +1,32 @@
+#ifndef __LINUX_TC_CSUM_H
+#define __LINUX_TC_CSUM_H
+
+#include <linux/types.h>
+#include <linux/pkt_cls.h>
+
+#define TCA_ACT_CSUM 16
+
+enum {
+	TCA_CSUM_UNSPEC,
+	TCA_CSUM_PARMS,
+	TCA_CSUM_TM,
+	__TCA_CSUM_MAX
+};
+#define TCA_CSUM_MAX (__TCA_CSUM_MAX - 1)
+
+enum {
+	TCA_CSUM_UPDATE_FLAG_IPV4HDR = 1,
+	TCA_CSUM_UPDATE_FLAG_ICMP    = 2,
+	TCA_CSUM_UPDATE_FLAG_IGMP    = 4,
+	TCA_CSUM_UPDATE_FLAG_TCP     = 8,
+	TCA_CSUM_UPDATE_FLAG_UDP     = 16,
+	TCA_CSUM_UPDATE_FLAG_UDPLITE = 32
+};
+
+struct tc_csum {
+	tc_gen;
+
+	__u32 update_flags;
+};
+
+#endif /* __LINUX_TC_CSUM_H */

index 3aa9f26..101cc83 100644
@@ -34,6 +34,7 @@ TCMODULES += m_mirred.o
 TCMODULES += m_nat.o
 TCMODULES += m_pedit.o
 TCMODULES += m_skbedit.o
+TCMODULES += m_csum.o
 TCMODULES += p_ip.o
 TCMODULES += p_icmp.o
 TCMODULES += p_tcp.o