[PATCH v2] vsprintf: add Bluetooth UUID %pU[rR] format specifier

[Marcel Holtmann]

The Bluetooth UUID is used in big endian reversed order. Add new
modifier to print a UUID in big endian, but where the input byte
stream is actually in reversed order.

This is similar to %pMR that allows to print a MAC address in
reversed order since that is how the Bluetooth BD_ADDR is
actually represented in a byte stream.

Signed-off-by: Marcel Holtmann <marcel@xxxxxxxxxxxx>
---
v2: Allow combinations of %pUlr etc.

 Documentation/printk-formats.txt |  6 ++++++
 lib/vsprintf.c                   | 40 ++++++++++++++++++++++++++++------------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 445ad74..1fd0e43 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -159,12 +159,18 @@ UUID/GUID addresses:
 	%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
 	%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
 	%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
+	%pUr	0f0e0d0c-0b0a-0908-0706-050403020100
+	%pUR	0F0E0D0C-0B0A-0908-0706-050403020100
 
 	For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
 	'b' and 'B' specifiers are used to specify a little endian order in
 	lower ('l') or upper case ('L') hex characters - and big endian order
 	in lower ('b') or upper case ('B') hex characters.
 
+	The additional 'r' and 'R' specifiers are used to specify reversed
+	big endian order in either lower ('r') or upper case ('R') hex
+	characters. This is useful for Bluetooth UUID addresses.
+
 	Where no additional specifiers are used the default little endian
 	order with lower case hex characters will be printed.
 
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 26559bd..d0f9188 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1106,20 +1106,32 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 	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;
+	bool reversed = false;
 
-	switch (*(++fmt)) {
-	case 'L':
-		uc = true;		/* fall-through */
-	case 'l':
-		index = le;
-		break;
-	case 'B':
-		uc = true;
-		break;
+	while (isalpha(*++fmt)) {
+		switch (*fmt) {
+		case 'L':
+			uc = true;		/* fall-through */
+		case 'l':
+			index = le;
+			break;
+		case 'B':
+			uc = true;
+			break;
+		case 'R':
+			uc = true;		/* fall-through */
+		case 'r':
+			reversed = true;
+			break;
+		}
 	}
 
 	for (i = 0; i < 16; i++) {
-		p = hex_byte_pack(p, addr[index[i]]);
+		if (reversed)
+			p = hex_byte_pack(p, addr[index[15 - i]]);
+		else
+			p = hex_byte_pack(p, addr[index[i]]);
+
 		switch (i) {
 		case 3:
 		case 5:
@@ -1199,10 +1211,14 @@ int kptr_restrict __read_mostly;
  *         B big endian UPPER case hex
  *         l little endian lower case hex
  *         L little endian UPPER case hex
+ *         r big endian lower case hex, reverse order (Bluetooth)
+ *         R big endian UPPER case hex, reverse order (Bluetooth)
  *           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]
+ *           big endian, reverse order output byte order is:
+ *             [15][14][13][12]-[11][10]-[9][8]-[7][6]-[5][4][3][2][1][0]
  * - 'V' For a struct va_format which contains a format string * and va_list *,
  *       call vsnprintf(->format, *->va_list).
  *       Implements a "recursive vsnprintf".
@@ -1572,8 +1588,8 @@ qualifier:
  * %pI6c print an IPv6 address as specified by RFC 5952
  * %pIS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address
  * %piS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address
- * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
- *   case.
+ * %pU[bBlLrR] print a UUID/GUID in big or little endian or reversed order
+ *   big endian using lower or upper case.
  * %*ph[CDN] a variable-length hex string with a separator (supports up to 64
  *           bytes of the input)
  * %n is ignored
-- 
1.8.3.1

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