ip link: proto_down config and display.

This patch adds support to set and display protodown on a switch port. The
switch driver can handle this error state by doing a phys down on the port.

One example user space application setting this flag is a multi-chassis
LAG application to handle split-brain situation on peer-link failure.

Example:
root@net-next:~# ip link set eth1 protodown on
root@net-next:~/iproute2# ip link show eth1
4: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:12:35:01 brd ff:ff:ff:ff:ff:ff protodown on
root@net-next:~/iproute2# ip link set eth1 protodown off
root@net-next:~/iproute2# ip link show eth1
4: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:12:35:01 brd ff:ff:ff:ff:ff:ff
root@net-next:~/iproute2#
Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>
Signed-off-by: Andy Gospodarek <gospo@cumulusnetworks.com>
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>

ip/ipaddress.c

@@ -744,6 +744,11 @@ int print_linkinfo(const struct sockaddr_nl *who,
 			fprintf(fp, " link-netnsid unknown");
 	}
 
+	if (tb[IFLA_PROTO_DOWN]) {
+		if (rta_getattr_u8(tb[IFLA_PROTO_DOWN]))
+			fprintf(fp, " protodown on ");
+	}
+
 	if (tb[IFLA_PROMISCUITY] && show_details)
 		fprintf(fp, " promiscuity %u ",
 			*(int*)RTA_DATA(tb[IFLA_PROMISCUITY]));

ip/iplink.c

@@ -85,6 +85,7 @@ void iplink_usage(void)
 	fprintf(stderr, "			  [ master DEVICE ]\n");
 	fprintf(stderr, "			  [ nomaster ]\n");
 	fprintf(stderr, "			  [ addrgenmode { eui64 | none } ]\n");
+	fprintf(stderr, "	                  [ protodown { on | off } ]\n");
 	fprintf(stderr, "       ip link show [ DEVICE | group GROUP ] [up] [master DEV] [type TYPE]\n");
 
 	if (iplink_have_newlink()) {
@@ -612,6 +613,18 @@ int iplink_parse(int argc, char **argv, struct iplink_req *req,
 				invarg("Invalid \"link-netnsid\" value\n", *argv);
 			addattr32(&req->n, sizeof(*req), IFLA_LINK_NETNSID,
 				  link_netnsid);
+		} else if (strcmp(*argv, "protodown") == 0) {
+			unsigned int proto_down;
+
+			NEXT_ARG();
+			if (strcmp(*argv, "on") == 0)
+				proto_down = 1;
+			else if (strcmp(*argv, "off") == 0)
+				proto_down = 0;
+			else
+				return on_off("protodown", *argv);
+			addattr8(&req->n, sizeof(*req), IFLA_PROTO_DOWN,
+				 proto_down);
 		} else {
 			if (strcmp(*argv, "dev") == 0) {
 				NEXT_ARG();

man/man8/ip-link.8.in

@@ -101,6 +101,8 @@ ip-link \- network device configuration
 .br
 .BR multicast " { " on " | " off " } |"
 .br
+.BR protodown " { " on " | " off " } |"
+.br
 .B  txqueuelen
 .IR PACKETS " |"
 .br
@@ -681,6 +683,12 @@ change the
 .B MULTICAST
 flag on the device.
 
+.TP
+.BR "protodown on " or " protodown off"
+change the
+.B PROTODOWN
+state on the device. Indicates that a protocol error has been detected on the port. Switch drivers can react to this error by doing a phys down on the switch port.
+
 .TP
 .BR "dynamic on " or " dynamic off"
 change the