[libmnl] examples: add arp cache dump example

diff --git a/examples/rtnl/Makefile.am b/examples/rtnl/Makefile.am
index 24769b6..e56365c 100644
--- a/examples/rtnl/Makefile.am
+++ b/examples/rtnl/Makefile.am
@@ -6,7 +6,8 @@  check_PROGRAMS = rtnl-addr-dump \
 		 rtnl-link-set \
 		 rtnl-route-add \
 		 rtnl-route-dump \
-		 rtnl-route-event
+		 rtnl-route-event \
+		 rtnl-arp-dump
 
 rtnl_addr_dump_SOURCES = rtnl-addr-dump.c
 rtnl_addr_dump_LDADD = ../../src/libmnl.la
@@ -34,3 +35,6 @@  rtnl_route_dump_LDADD = ../../src/libmnl.la
 
 rtnl_route_event_SOURCES = rtnl-route-event.c
 rtnl_route_event_LDADD = ../../src/libmnl.la
+
+rtnl_arp_dump_SOURCES = rtnl-arp-dump.c
+rtnl_arp_dump_LDADD = ../../src/libmnl.la
diff --git a/examples/rtnl/rtnl-arp-dump.c b/examples/rtnl/rtnl-arp-dump.c
new file mode 100644
index 0000000..fc0f205
--- /dev/null
+++ b/examples/rtnl/rtnl-arp-dump.c
@@ -0,0 +1,161 @@ 
+/* This example is placed in the public domain. */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <time.h>
+#include <arpa/inet.h>
+
+#include <libmnl/libmnl.h>
+#include <linux/if.h>
+#include <linux/if_link.h>
+#include <linux/rtnetlink.h>
+
+static int data_attr_cb(const struct nlattr *attr, void *data)
+{
+	const struct nlattr **tb = data;
+	int type = mnl_attr_get_type(attr);
+
+	/* skip unsupported attribute in user-space */
+	if (mnl_attr_type_valid(attr, IFA_MAX) < 0)
+		return MNL_CB_OK;
+
+	switch(type) {
+	case NDA_DST:
+		if (mnl_attr_validate(attr, MNL_TYPE_BINARY) < 0) {
+			perror("mnl_attr_validate");
+			return MNL_CB_ERROR;
+		}
+		break;
+	case NDA_LLADDR:
+		if (mnl_attr_validate(attr, MNL_TYPE_BINARY) < 0) {
+			perror("mnl_attr_validate");
+			return MNL_CB_ERROR;
+		}
+		break;
+	}
+	tb[type] = attr;
+	return MNL_CB_OK;
+}
+
+static int data_cb(const struct nlmsghdr *nlh, void *data)
+{
+	struct nlattr *tb[IFA_MAX + 1] = {};
+	struct ndmsg *ndm = mnl_nlmsg_get_payload(nlh);
+
+	printf("index=%d family=%d ", ndm->ndm_ifindex, ndm->ndm_family);
+
+	mnl_attr_parse(nlh, sizeof(*ndm), data_attr_cb, tb);
+	printf("dst=");
+	if (tb[NDA_DST]) {
+		void *addr = mnl_attr_get_payload(tb[NDA_DST]);
+		char out[INET6_ADDRSTRLEN];
+
+		if (inet_ntop(ndm->ndm_family, addr, out, sizeof(out)))
+			printf("%s ", out);
+	}
+
+	mnl_attr_parse(nlh, sizeof(*ndm), data_attr_cb, tb);
+	printf("lladdr=");
+	if (tb[NDA_LLADDR]) {
+		void *addr = mnl_attr_get_payload(tb[NDA_LLADDR]);
+		unsigned char lladdr[6] = {0};
+
+		if (memcpy(&lladdr, addr, 6))
+			printf("%02x:%02x:%02x:%02x:%02x:%02x ", lladdr[0], lladdr[1], lladdr[2], lladdr[3], lladdr[4], lladdr[5]);
+	}
+
+	printf("state=");
+	switch(ndm->ndm_state) {
+	case NUD_INCOMPLETE:
+		printf("incomplete ");
+		break;
+	case NUD_REACHABLE:
+		printf("reachable ");
+		break;
+	case NUD_STALE:
+		printf("stale ");
+		break;
+	case NUD_DELAY:
+		printf("delay ");
+		break;
+	case NUD_PROBE:
+		printf("probe ");
+		break;
+	case NUD_FAILED:
+		printf("failed ");
+		break;
+	case NUD_NOARP:
+		printf("noarp ");
+		break;
+	case NUD_PERMANENT:
+		printf("permanent ");
+		break;
+	default:
+		printf("%d ", ndm->ndm_state);
+		break;
+	}
+
+	printf("\n");
+	return MNL_CB_OK;
+}
+
+int main(int argc, char *argv[])
+{
+	struct mnl_socket *nl;
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh;
+	struct rtgenmsg *rt;
+	int ret;
+	unsigned int seq, portid;
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s <inet|inet6>\n", argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	nlh = mnl_nlmsg_put_header(buf);
+	nlh->nlmsg_type	= RTM_GETNEIGH;
+	nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+	nlh->nlmsg_seq = seq = time(NULL);
+
+	rt = mnl_nlmsg_put_extra_header(nlh, sizeof(struct rtgenmsg));
+	if (strcmp(argv[1], "inet") == 0)
+		rt->rtgen_family = AF_INET;
+	else if (strcmp(argv[1], "inet6") == 0)
+		rt->rtgen_family = AF_INET6;
+
+	nl = mnl_socket_open(NETLINK_ROUTE);
+	if (nl == NULL) {
+		perror("mnl_socket_open");
+		exit(EXIT_FAILURE);
+	}
+
+	if (mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0) {
+		perror("mnl_socket_bind");
+		exit(EXIT_FAILURE);
+	}
+	portid = mnl_socket_get_portid(nl);
+
+	if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
+		perror("mnl_socket_sendto");
+		exit(EXIT_FAILURE);
+	}
+
+	ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
+	while (ret > 0) {
+		ret = mnl_cb_run(buf, ret, seq, portid, data_cb, NULL);
+		if (ret <= MNL_CB_STOP)
+			break;
+		ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
+	}
+
+	if (ret == -1) {
+		perror("error");
+		exit(EXIT_FAILURE);
+	}
+
+	mnl_socket_close(nl);
+
+	return 0;
+}