printk: add %pM format specifier for MAC addresses

Add format specifiers for printing out six colon-separated bytes:

MAC addresses (%pM):
xx:xx:xx:xx:xx:xx

%#pM is also supported and omits the colon separators.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/vsprintf.c

@@ -581,6 +581,23 @@ static char *resource_string(char *buf, char *end, struct resource *res, int fie
 	return string(buf, end, sym, field_width, precision, flags);
 }
 
+static char *mac_address_string(char *buf, char *end, u8 *addr, int field_width,
+				int precision, int flags)
+{
+	char mac_addr[6 * 3]; /* (6 * 2 hex digits), 5 colons and trailing zero */
+	char *p = mac_addr;
+	int i;
+
+	for (i = 0; i < 6; i++) {
+		p = pack_hex_byte(p, addr[i]);
+		if (!(flags & SPECIAL) && i != 5)
+			*p++ = ':';
+	}
+	*p = '\0';
+
+	return string(buf, end, mac_addr, field_width, precision, flags & ~SPECIAL);
+}
+
 /*
  * Show a '%p' thing.  A kernel extension is that the '%p' is followed
  * by an extra set of alphanumeric characters that are extended format
@@ -592,6 +609,8 @@ static char *resource_string(char *buf, char *end, struct resource *res, int fie
  * - 'S' For symbolic direct pointers
  * - 'R' For a struct resource pointer, it prints the range of
  *       addresses (not the name nor the flags)
+ * - 'M' For a 6-byte MAC address, it prints the address in the
+ *       usual colon-separated hex notation
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
@@ -607,6 +626,8 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr, int field
 		return symbol_string(buf, end, ptr, field_width, precision, flags);
 	case 'R':
 		return resource_string(buf, end, ptr, field_width, precision, flags);
+	case 'M':
+		return mac_address_string(buf, end, ptr, field_width, precision, flags);
 	}
 	flags |= SMALL;
 	if (field_width == -1) {