Documentation: update printk-formats.txt

This patch updates the incomplete documentation concerning the printk
extended format specifiers.
Signed-off-by: NAndrew Murray <amurray@mpc-data.co.uk>
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/printk-formats.txt

@@ -9,7 +9,121 @@ If variable is of Type,		use printk format specifier:
 		size_t			%zu or %zx
 		ssize_t			%zd or %zx
 
-Raw pointer value SHOULD be printed with %p.
+Raw pointer value SHOULD be printed with %p. The kernel supports
+the following extended format specifiers for pointer types:
+
+Symbols/Function Pointers:
+
+	%pF	versatile_init+0x0/0x110
+	%pf	versatile_init
+	%pS	versatile_init+0x0/0x110
+	%ps	versatile_init
+	%pB	prev_fn_of_versatile_init+0x88/0x88
+
+	For printing symbols and function pointers. The 'S' and 's' specifiers
+	result in the symbol name with ('S') or without ('s') offsets. Where
+	this is used on a kernel without KALLSYMS - the symbol address is
+	printed instead.
+
+	The 'B' specifier results in the symbol name with offsets and should be
+	used when printing stack backtraces. The specifier takes into
+	consideration the effect of compiler optimisations which may occur
+	when tail-call's are used and marked with the noreturn GCC attribute.
+
+	On ia64, ppc64 and parisc64 architectures function pointers are
+	actually function descriptors which must first be resolved. The 'F' and
+	'f' specifiers perform this resolution and then provide the same
+	functionality as the 'S' and 's' specifiers.
+
+Kernel Pointers:
+
+	%pK	0x01234567 or 0x0123456789abcdef
+
+	For printing kernel pointers which should be hidden from unprivileged
+	users. The behaviour of %pK depends on the kptr_restrict sysctl - see
+	Documentation/sysctl/kernel.txt for more details.
+
+Struct Resources:
+
+	%pr	[mem 0x60000000-0x6fffffff flags 0x2200] or
+		[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
+	%pR	[mem 0x60000000-0x6fffffff pref] or
+		[mem 0x0000000060000000-0x000000006fffffff pref]
+
+	For printing struct resources. The 'R' and 'r' specifiers result in a
+	printed resource with ('R') or without ('r') a decoded flags member.
+
+MAC/FDDI addresses:
+
+	%pM	00:01:02:03:04:05
+	%pMF	00-01-02-03-04-05
+	%pm	000102030405
+
+	For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
+	specifiers result in a printed address with ('M') or without ('m') byte
+	separators. The default byte separator is the colon (':').
+
+	Where FDDI addresses are concerned the 'F' specifier can be used after
+	the 'M' specifier to use dash ('-') separators instead of the default
+	separator.
+
+IPv4 addresses:
+
+	%pI4	1.2.3.4
+	%pi4	001.002.003.004
+	%p[Ii][hnbl]
+
+	For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
+	specifiers result in a printed address with ('i4') or without ('I4')
+	leading zeros.
+
+	The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
+	host, network, big or little endian order addresses respectively. Where
+	no specifier is provided the default network/big endian order is used.
+
+IPv6 addresses:
+
+	%pI6	0001:0002:0003:0004:0005:0006:0007:0008
+	%pi6	00010002000300040005000600070008
+	%pI6c	1:2:3:4:5:6:7:8
+
+	For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
+	specifiers result in a printed address with ('I6') or without ('i6')
+	colon-separators. Leading zeros are always used.
+
+	The additional 'c' specifier can be used with the 'I' specifier to
+	print a compressed IPv6 address as described by
+	http://tools.ietf.org/html/rfc5952
+
+UUID/GUID addresses:
+
+	%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
+	%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F
+	%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
+	%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
+
+	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.
+
+	Where no additional specifiers are used the default little endian
+	order with lower case hex characters will be printed.
+
+struct va_format:
+
+	%pV
+
+	For printing struct va_format structures. These contain a format string
+	and va_list as follows:
+
+	struct va_format {
+		const char *fmt;
+		va_list *va;
+	};
+
+	Do not use this feature without some mechanism to verify the
+	correctness of the format string and va_list arguments.
 
 u64 SHOULD be printed with %llu/%llx, (unsigned long long):
 
@@ -32,4 +146,5 @@ Reminder: sizeof() result is of type size_t.
 Thank you for your cooperation and attention.
 
 
-By Randy Dunlap <rdunlap@xenotime.net>
+By Randy Dunlap <rdunlap@xenotime.net> and
+Andrew Murray <amurray@mpc-data.co.uk>