mptcp: add the mib for data checksum

This patch added the mib for the data checksum, MPTCP_MIB_DATACSUMERR.

Acked-by: Paolo Abeni <[e-mail]>
Signed-off-by: Geliang Tang <[e-mail]>
Signed-off-by: Mat Martineau <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/mptcp/mib.c

···
 	SNMP_MIB_ITEM("MPJoinAckHMacFailure", MPTCP_MIB_JOINACKMAC),
 	SNMP_MIB_ITEM("DSSNotMatching", MPTCP_MIB_DSSNOMATCH),
 	SNMP_MIB_ITEM("InfiniteMapRx", MPTCP_MIB_INFINITEMAPRX),
+	SNMP_MIB_ITEM("DataCsumErr", MPTCP_MIB_DATACSUMERR),
 	SNMP_MIB_ITEM("OFOQueueTail", MPTCP_MIB_OFOQUEUETAIL),
 	SNMP_MIB_ITEM("OFOQueue", MPTCP_MIB_OFOQUEUE),
 	SNMP_MIB_ITEM("OFOMerge", MPTCP_MIB_OFOMERGE),

net/mptcp/mib.h

···
 	MPTCP_MIB_JOINACKMAC,		/* HMAC was wrong on ACK + MP_JOIN */
 	MPTCP_MIB_DSSNOMATCH,		/* Received a new mapping that did not match the previous one */
 	MPTCP_MIB_INFINITEMAPRX,	/* Received an infinite mapping */
+	MPTCP_MIB_DATACSUMERR,		/* The data checksum fail */
 	MPTCP_MIB_OFOQUEUETAIL,	/* Segments inserted into OoO queue tail */
 	MPTCP_MIB_OFOQUEUE,		/* Segments inserted into OoO queue */
 	MPTCP_MIB_OFOMERGE,		/* Segments merged in OoO queue */

net/mptcp/subflow.c

···
 	header.csum = 0;
 
 	csum = csum_partial(&header, sizeof(header), subflow->map_data_csum);
-	if (unlikely(csum_fold(csum)))
+	if (unlikely(csum_fold(csum))) {
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DATACSUMERR);
 		return subflow->mp_join ? MAPPING_INVALID : MAPPING_DUMMY;
+	}
 
 	return MAPPING_OK;
 }