ipneigh: neigh get support

This patch adds support to lookup a neigh entry
using recently added support in the kernel using RTM_GETNEIGH

example:
$ip neigh get 10.0.2.4 dev test-dummy0
10.0.2.4 dev test-dummy0 lladdr de:ad:be:ef:13:37 PERMANENT

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Tested-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>

ip/ipneigh.c

@@ -55,6 +55,7 @@ static void usage(void)
 		"\n"
 		"	ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ]\n"
 		"				  [ vrf NAME ]\n"
+		"	ip neigh get { ADDR | proxy ADDR } dev DEV\n"
 		"\n"
 		"STATE := { permanent | noarp | stale | reachable | none |\n"
 		"           incomplete | delay | probe | failed }\n");
@@ -599,6 +600,82 @@ static int do_show_or_flush(int argc, char **argv, int flush)
 	return 0;
 }
 
+static int ipneigh_get(int argc, char **argv)
+{
+	struct {
+		struct nlmsghdr	n;
+		struct ndmsg		ndm;
+		char			buf[1024];
+	} req = {
+		.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ndmsg)),
+		.n.nlmsg_flags = NLM_F_REQUEST,
+		.n.nlmsg_type = RTM_GETNEIGH,
+		.ndm.ndm_family = preferred_family,
+	};
+	struct nlmsghdr *answer;
+	char  *d = NULL;
+	int dst_ok = 0;
+	int dev_ok = 0;
+	inet_prefix dst;
+
+	while (argc > 0) {
+		if (strcmp(*argv, "dev") == 0) {
+			NEXT_ARG();
+			d = *argv;
+			dev_ok = 1;
+		} else if (matches(*argv, "proxy") == 0) {
+			NEXT_ARG();
+			if (matches(*argv, "help") == 0)
+				usage();
+			if (dst_ok)
+				duparg("address", *argv);
+			get_addr(&dst, *argv, preferred_family);
+			dst_ok = 1;
+			dev_ok = 1;
+			req.ndm.ndm_flags |= NTF_PROXY;
+		} else {
+			if (strcmp(*argv, "to") == 0)
+				NEXT_ARG();
+
+			if (matches(*argv, "help") == 0)
+				usage();
+			if (dst_ok)
+				duparg2("to", *argv);
+			get_addr(&dst, *argv, preferred_family);
+			dst_ok = 1;
+		}
+		argc--; argv++;
+	}
+
+	if (!dev_ok || !dst_ok || dst.family == AF_UNSPEC) {
+		fprintf(stderr, "Device and address are required arguments.\n");
+		return -1;
+	}
+
+	req.ndm.ndm_family = dst.family;
+	if (addattr_l(&req.n, sizeof(req), NDA_DST, &dst.data, dst.bytelen) < 0)
+		return -1;
+
+	if (d) {
+		req.ndm.ndm_ifindex = ll_name_to_index(d);
+		if (!req.ndm.ndm_ifindex) {
+			fprintf(stderr, "Cannot find device \"%s\"\n", d);
+			return -1;
+		}
+	}
+
+	if (rtnl_talk(&rth, &req.n, &answer) < 0)
+		return -2;
+
+	ipneigh_reset_filter(0);
+	if (print_neigh(answer, stdout) < 0) {
+		fprintf(stderr, "An error :-)\n");
+		return -1;
+	}
+
+	return 0;
+}
+
 int do_ipneigh(int argc, char **argv)
 {
 	if (argc > 0) {
@@ -611,10 +688,8 @@ int do_ipneigh(int argc, char **argv)
 			return ipneigh_modify(RTM_NEWNEIGH, NLM_F_CREATE|NLM_F_REPLACE, argc-1, argv+1);
 		if (matches(*argv, "delete") == 0)
 			return ipneigh_modify(RTM_DELNEIGH, 0, argc-1, argv+1);
-		if (matches(*argv, "get") == 0) {
+		if (matches(*argv, "get") == 0)
-			fprintf(stderr, "Sorry, \"neigh get\" is not implemented :-(\n");
+			return ipneigh_get(argc-1, argv+1);
-			return -1;
-		}
 		if (matches(*argv, "show") == 0 ||
 		    matches(*argv, "lst") == 0 ||
 		    matches(*argv, "list") == 0)

man/man8/ip-neighbour.8

@@ -37,6 +37,12 @@ ip-neighbour \- neighbour/arp tables management.
 .B  vrf
 .IR NAME " ] "
 
+.ti -8
+.B ip neigh get
+.IR ADDR
+.B  dev
+.IR DEV
+
 .ti -8
 .IR STATE " := {"
 .BR permanent " | " noarp " | " stale " | " reachable " | " none " |"
@@ -231,6 +237,23 @@ twice,
 also dumps all the deleted neighbours.
 .RE
 
+.TP
+ip neigh get
+lookup a neighbour entry to a destination given a device
+.RS
+
+.TP
+.BI proxy
+indicates whether we should lookup a proxy neigbour entry
+
+.TP
+.BI to " ADDRESS " (default)
+the prefix selecting the neighbour to query.
+
+.TP
+.BI dev " NAME"
+get neighbour entry attached to this device.
+
 .SH EXAMPLES
 .PP
 ip neighbour
@@ -242,6 +265,12 @@ ip neigh flush dev eth0
 .RS
 Removes entries in the neighbour table on device eth0.
 .RE
+.PP
+ip neigh get 10.0.1.10 dev eth0
+.RS
+Performs a neighbour lookup in the kernel and returns
+a neighbour entry.
+.RE
 
 .SH SEE ALSO
 .br