Documentation: update printk-formats.txt

This patch updates the incomplete documentation concerning the printk
extended format specifiers.

Signed-off-by: Andrew Murray <amurray@mpc-data.co.uk>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 1b5a5dd..5df176e 100644 (file)
--- a/Documentation/printk-formats.txt
+++ b/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>