UUID/GUIDs are somewhat common in kernel source.

Standardize the printed style of UUID/GUIDs by using
another extension to %p.

%pUb:   01020304-0506-0708-090a-0b0c0d0e0f10
%pUB:   01020304-0506-0708-090A-0B0C0D0E0F10 (upper case)
%pUl:   04030201-0605-0807-090a-0b0c0d0e0f10
%pUL:   04030201-0605-0807-090A-0B0C0D0E0F10 (upper case)

%pU defaults to %pUb
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Jeff Garzik <jgarzik@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Alex Elder <aelder@sgi.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Artem Bityutskiy <dedekind@infradead.org>
Cc: Adrian Hunter <adrian.hunter@nokia.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/vsprintf.c

@@ -842,6 +842,52 @@ static char *ip4_addr_string(char *buf, char *end, const u8 *addr,
 	return string(buf, end, ip4_addr, spec);
 }
 
+static char *uuid_string(char *buf, char *end, const u8 *addr,
+			 struct printf_spec spec, const char *fmt)
+{
+	char uuid[sizeof("xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx")];
+	char *p = uuid;
+	int i;
+	static const u8 be[16] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
+	static const u8 le[16] = {3,2,1,0,5,4,7,6,8,9,10,11,12,13,14,15};
+	const u8 *index = be;
+	bool uc = false;
+
+	switch (*(++fmt)) {
+	case 'L':
+		uc = true;		/* fall-through */
+	case 'l':
+		index = le;
+		break;
+	case 'B':
+		uc = true;
+		break;
+	}
+
+	for (i = 0; i < 16; i++) {
+		p = pack_hex_byte(p, addr[index[i]]);
+		switch (i) {
+		case 3:
+		case 5:
+		case 7:
+		case 9:
+			*p++ = '-';
+			break;
+		}
+	}
+
+	*p = 0;
+
+	if (uc) {
+		p = uuid;
+		do {
+			*p = toupper(*p);
+		} while (*(++p));
+	}
+
+	return string(buf, end, uuid, spec);
+}
+
 /*
  * Show a '%p' thing.  A kernel extension is that the '%p' is followed
  * by an extra set of alphanumeric characters that are extended format
@@ -866,6 +912,18 @@ static char *ip4_addr_string(char *buf, char *end, const u8 *addr,
  *       IPv4 uses dot-separated decimal with leading 0's (010.123.045.006)
  * - 'I6c' for IPv6 addresses printed as specified by
  *       http://www.ietf.org/id/draft-kawamura-ipv6-text-representation-03.txt
+ * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form
+ *       "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+ *       Options for %pU are:
+ *         b big endian lower case hex (default)
+ *         B big endian UPPER case hex
+ *         l little endian lower case hex
+ *         L little endian UPPER case hex
+ *           big endian output byte order is:
+ *             [0][1][2][3]-[4][5]-[6][7]-[8][9]-[10][11][12][13][14][15]
+ *           little endian output byte order is:
+ *             [3][2][1][0]-[5][4]-[7][6]-[8][9]-[10][11][12][13][14][15]
+ *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
  * pointer to the real address.
@@ -880,9 +938,9 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'F':
 	case 'f':
 		ptr = dereference_function_descriptor(ptr);
-	case 's':
 		/* Fallthrough */
 	case 'S':
+	case 's':
 		return symbol_string(buf, end, ptr, spec, *fmt);
 	case 'R':
 	case 'r':
@@ -906,6 +964,8 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return ip4_addr_string(buf, end, ptr, spec, fmt);
 		}
 		break;
+	case 'U':
+		return uuid_string(buf, end, ptr, spec, fmt);
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {