samples: bpf: Convert ARP table network order fields into readable format

The ARP table that is dumped when the xdp_router_ipv4 process is launched
has the IP address & MAC address in non-readable network byte order format,
also the alignment is off when printing the table.

Address HwAddress
160000e0                1600005e0001
ff96a8c0                ffffffffffff
faffffef                faff7f5e0001
196a8c0		9607871293ea
fb0000e0                fb00005e0001
0               0
196a8c0		9607871293ea
ffff11ac                ffffffffffff
faffffef                faff7f5e0001
fb0000e0                fb00005e0001
160000e0                1600005e0001
160000e0                1600005e0001
faffffef                faff7f5e0001
fb0000e0                fb00005e0001
40011ac         40011ac4202

Fix this by converting the "Address" field from network byte order Hex into
dotted decimal notation IPv4 format and "HwAddress" field from network byte
order Hex into Colon separated Hex format. Also fix the aligntment of the
fields in the ARP table.

Address         HwAddress
224.0.0.22      01:00:5e:00:00:16
192.168.150.255 ff:ff:ff:ff:ff:ff
239.255.255.250 01:00:5e:7f:ff:fa
192.168.150.1	ea:93:12:87:07:96
224.0.0.251     01:00:5e:00:00:fb
0.0.0.0         00:00:00:00:00:00
192.168.150.1	ea:93:12:87:07:96
172.17.255.255  ff:ff:ff:ff:ff:ff
239.255.255.250 01:00:5e:7f:ff:fa
224.0.0.251     01:00:5e:00:00:fb
224.0.0.22      01:00:5e:00:00:16
224.0.0.22      01:00:5e:00:00:16
239.255.255.250 01:00:5e:7f:ff:fa
224.0.0.251     01:00:5e:00:00:fb
172.17.0.4      02:42:ac:11:00:04
Signed-off-by: Gokul Sivakumar <gokulkumar792@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210919080305.173588-2-gokulkumar792@gmail.com

samples/bpf/xdp_router_ipv4_user.c

@@ -397,8 +397,12 @@ static void read_arp(struct nlmsghdr *nh, int nll)
 
 	if (nh->nlmsg_type == RTM_GETNEIGH)
 		printf("READING arp entry\n");
-	printf("Address\tHwAddress\n");
+	printf("Address         HwAddress\n");
 	for (; NLMSG_OK(nh, nll); nh = NLMSG_NEXT(nh, nll)) {
+		struct in_addr dst_addr;
+		char mac_str[18];
+		int len = 0, i;
+
 		rt_msg = (struct ndmsg *)NLMSG_DATA(nh);
 		rt_attr = (struct rtattr *)RTM_RTA(rt_msg);
 		ndm_family = rt_msg->ndm_family;
@@ -419,7 +423,14 @@ static void read_arp(struct nlmsghdr *nh, int nll)
 		}
 		arp_entry.dst = atoi(dsts);
 		arp_entry.mac = atol(mac);
-		printf("%x\t\t%llx\n", arp_entry.dst, arp_entry.mac);
+
+		dst_addr.s_addr = arp_entry.dst;
+		for (i = 0; i < 6; i++)
+			len += snprintf(mac_str + len, 18 - len, "%02llx%s",
+					((arp_entry.mac >> i * 8) & 0xff),
+					i < 5 ? ":" : "");
+		printf("%-16s%s\n", inet_ntoa(dst_addr), mac_str);
+
 		if (ndm_family == AF_INET) {
 			if (bpf_map_lookup_elem(exact_match_map_fd,
 						&arp_entry.dst,
@@ -728,7 +739,7 @@ int main(int ac, char **argv)
 
 	printf("\n*******************ROUTE TABLE*************************\n");
 	get_route_table(AF_INET);
-	printf("*******************ARP TABLE***************************\n\n\n");
+	printf("\n*******************ARP TABLE***************************\n");
 	get_arp_table(AF_INET);
 	if (monitor_route() < 0) {
 		printf("Error in receiving route update");