ROSE: Add rose_ntop implementation.

ROSE addresses are ten digit numbers, basically like North American
telephone numbers.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David Ahern <dsahern@kernel.org>
diff --git a/Makefile b/Makefile
index df894d5..5eddd50 100644
--- a/Makefile
+++ b/Makefile
@@ -43,6 +43,9 @@
 #options for AX.25
 ADDLIB+=ax25_ntop.o
 
+#options for AX.25
+ADDLIB+=rose_ntop.o
+
 #options for mpls
 ADDLIB+=mpls_ntop.o mpls_pton.o
 
diff --git a/include/utils.h b/include/utils.h
index 6ab2fa7..b6c468e 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -200,6 +200,8 @@
 
 const char *ax25_ntop(int af, const void *addr, char *str, socklen_t len);
 
+const char *rose_ntop(int af, const void *addr, char *buf, socklen_t buflen);
+
 const char *mpls_ntop(int af, const void *addr, char *str, size_t len);
 int mpls_pton(int af, const char *src, void *addr, size_t alen);
 
diff --git a/lib/rose_ntop.c b/lib/rose_ntop.c
new file mode 100644
index 0000000..c9ba712
--- /dev/null
+++ b/lib/rose_ntop.c
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <string.h>
+#include <errno.h>
+
+#include <linux/netdevice.h>
+#include <linux/if_arp.h>
+#include <linux/sockios.h>
+#include <linux/rose.h>
+
+#include "rt_names.h"
+#include "utils.h"
+
+static const char *rose_ntop1(const rose_address *src, char *dst,
+			      socklen_t size)
+{
+	char *p = dst;
+	int i;
+
+	if (size < 10)
+		return NULL;
+
+	for (i = 0; i < 5; i++) {
+		*p++ = '0' + ((src->rose_addr[i] >> 4) & 0xf);
+		*p++ = '0' + ((src->rose_addr[i]     ) & 0xf);
+	}
+
+	if (size == 10)
+		return dst;
+
+	*p = '\0';
+
+	return dst;
+}
+
+const char *rose_ntop(int af, const void *addr, char *buf, socklen_t buflen)
+{
+	switch (af) {
+	case AF_ROSE:
+		errno = 0;
+		return rose_ntop1((rose_address *)addr, buf, buflen);
+
+	default:
+		errno = EAFNOSUPPORT;
+	}
+
+	return NULL;
+}