util: Helper for formatting MAC addresses

There are a couple of places where we somewhat messily open code formatting
an Ethernet like MAC address for display.  Add an eth_ntop() helper for
this.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

4 files changed, 27 insertions, 7 deletions

diff --git a/conf.c b/conf.c
index ed097bd..830f91a 100644
--- a/conf.c
+++ b/conf.c
@@ -921,7 +921,8 @@ pasta_opts:
  */
 static void conf_print(const struct ctx *c)
 {
-	char buf4[INET_ADDRSTRLEN], buf6[INET6_ADDRSTRLEN], ifn[IFNAMSIZ];
+	char buf4[INET_ADDRSTRLEN], buf6[INET6_ADDRSTRLEN];
+	char bufmac[ETH_ADDRSTRLEN], ifn[IFNAMSIZ];
 	int i;
 
 	info("Template interface: %s%s%s%s%s",
@@ -955,9 +956,7 @@ static void conf_print(const struct ctx *c)
 		info("Namespace interface: %s", c->pasta_ifn);
 
 	info("MAC:");
-	info("    host: %02x:%02x:%02x:%02x:%02x:%02x",
-	     c->mac[0], c->mac[1], c->mac[2],
-	     c->mac[3], c->mac[4], c->mac[5]);
+	info("    host: %s", eth_ntop(c->mac, bufmac, sizeof(bufmac)));
 
 	if (c->ifi4) {
 		if (!c->no_dhcp) {
diff --git a/dhcp.c b/dhcp.c
index aa9f59d..acc5b03 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -276,6 +276,7 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len)
 int dhcp(const struct ctx *c, const struct pool *p)
 {
 	size_t mlen, dlen, offset = 0, opt_len, opt_off = 0;
+	char macstr[ETH_ADDRSTRLEN];
 	const struct ethhdr *eh;
 	const struct iphdr *iph;
 	const struct udphdr *uh;
@@ -340,9 +341,7 @@ int dhcp(const struct ctx *c, const struct pool *p)
 		return -1;
 	}
 
-	info("    from %02x:%02x:%02x:%02x:%02x:%02x",
-	     m->chaddr[0], m->chaddr[1], m->chaddr[2],
-	     m->chaddr[3], m->chaddr[4], m->chaddr[5]);
+	info("    from %s", eth_ntop(m->chaddr, macstr, sizeof(macstr)));
 
 	m->yiaddr = c->ip4.addr;
 	mask.s_addr = htonl(0xffffffff << (32 - c->ip4.prefix_len));
diff --git a/util.c b/util.c
index 0b41404..7cb2c10 100644
--- a/util.c
+++ b/util.c
@@ -676,6 +676,25 @@ const char *sockaddr_ntop(const void *sa, char *dst, socklen_t size)
 	return dst;
 }
 
+/** eth_ntop() - Convert an Ethernet MAC address to text format
+ * @mac:	MAC address
+ * @dst:	Output buffer, minimum ETH_ADDRSTRLEN bytes
+ * @size:	Size of buffer at @dst
+ *
+ * Return: On success, a non-null pointer to @dst, NULL on failure
+ */
+const char *eth_ntop(const unsigned char *mac, char *dst, size_t size)
+{
+	int len;
+
+	len = snprintf(dst, size, "%02x:%02x:%02x:%02x:%02x:%02x",
+		       mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
+	if (len < 0 || (size_t)len >= size)
+		return NULL;
+
+	return dst;
+}
+
 /** str_ee_origin() - Convert socket extended error origin to a string
  * @ee:		Socket extended error structure
  *
diff --git a/util.h b/util.h
index cb4d181..a716849 100644
--- a/util.h
+++ b/util.h
@@ -215,9 +215,12 @@ static inline const char *af_name(sa_family_t af)
 
 #define SOCKADDR_STRLEN		MAX(SOCKADDR_INET_STRLEN, SOCKADDR_INET6_STRLEN)
 
+#define ETH_ADDRSTRLEN		(sizeof("00:11:22:33:44:55"))
+
 struct sock_extended_err;
 
 const char *sockaddr_ntop(const void *sa, char *dst, socklen_t size);
+const char *eth_ntop(const unsigned char *mac, char *dst, size_t size);
 const char *str_ee_origin(const struct sock_extended_err *ee);
 
 /**