printk-formats.txt: standardize document format

=========================================

How to get printk format specifiers right

=========================================

:Author: Randy Dunlap <rdunlap@infradead.org>

:Author: Andrew Murray <amurray@mpc-data.co.uk>

Integer types

=============

::

	If variable is of Type,		use printk format specifier:

---------------------------------------------------------

	------------------------------------------------------------

		int			%d or %x

		unsigned int		%u or %x

		long			%ld or %lx

		s64			%lld or %llx

		u64			%llu or %llx

If <type> is dependent on a config option for its size (e.g., sector_t,

blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a

format specifier of its largest possible type and explicitly cast to it.

Example:

If <type> is dependent on a config option for its size (e.g., ``sector_t``,

``blkcnt_t``) or is architecture-dependent for its size (e.g., ``tcflag_t``),

use a format specifier of its largest possible type and explicitly cast to it.

Example::

	printk("test: sector number/total blocks: %llu/%llu\n",

		(unsigned long long)sector, (unsigned long long)blockcount);

Reminder: sizeof() result is of type size_t.

Reminder: ``sizeof()`` result is of type ``size_t``.

The kernel's printf does not support %n. For obvious reasons, floating

point formats (%e, %f, %g, %a) are also not recognized. Use of any

The kernel's printf does not support ``%n``. For obvious reasons, floating

point formats (``%e, %f, %g, %a``) are also not recognized. Use of any

unsupported specifier or length qualifier results in a WARN and early

return from vsnprintf.

Raw pointer value SHOULD be printed with %p. The kernel supports

the following extended format specifiers for pointer types:

Symbols/Function Pointers:

Symbols/Function Pointers

=========================

::

	%pF	versatile_init+0x0/0x110

	%pf	versatile_init

	%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

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

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.

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.

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

===============

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

users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see

Documentation/sysctl/kernel.txt for more details.

Struct Resources:

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.

For printing struct resources. The ``R`` and ``r`` specifiers result in a

printed resource with (``R``) or without (``r``) a decoded flags member.

Passed by reference.

Physical addresses types phys_addr_t:

Physical addresses types ``phys_addr_t``

========================================

::

	%pa[p]	0x01234567 or 0x0123456789abcdef

	For printing a phys_addr_t type (and its derivatives, such as

	resource_size_t) which can vary based on build options, regardless of

For printing a ``phys_addr_t`` type (and its derivatives, such as

``resource_size_t``) which can vary based on build options, regardless of

the width of the CPU data path. Passed by reference.

DMA addresses types dma_addr_t:

DMA addresses types ``dma_addr_t``

==================================

::

	%pad	0x01234567 or 0x0123456789abcdef

	For printing a dma_addr_t type which can vary based on build options,

For printing a ``dma_addr_t`` type which can vary based on build options,

regardless of the width of the CPU data path. Passed by reference.

Raw buffer as an escaped string:

Raw buffer as an escaped string

===============================

::

	%*pE[achnops]

	For printing raw buffer as an escaped string. For the following buffer

For printing raw buffer as an escaped string. For the following buffer::

		1b 62 20 5c 43 07 22 90 0d 5d

few examples show how the conversion would be done (the result string

	without surrounding quotes):

without surrounding quotes)::

		%*pE		"\eb \C\a"\220\r]"

		%*pEhp		"\x1bb \C\x07"\x90\x0d]"

		%*pEa		"\e\142\040\\\103\a\042\220\r\135"

The conversion rules are applied according to an optional combination

	of flags (see string_escape_mem() kernel documentation for the

of flags (see :c:func:`string_escape_mem` kernel documentation for the

details):

		a - ESCAPE_ANY

		c - ESCAPE_SPECIAL

		h - ESCAPE_HEX

		n - ESCAPE_NULL

		o - ESCAPE_OCTAL

		p - ESCAPE_NP

		s - ESCAPE_SPACE

	- ``a`` - ESCAPE_ANY

	- ``c`` - ESCAPE_SPECIAL

	- ``h`` - ESCAPE_HEX

	- ``n`` - ESCAPE_NULL

	- ``o`` - ESCAPE_OCTAL

	- ``p`` - ESCAPE_NP

	- ``s`` - ESCAPE_SPACE

By default ESCAPE_ANY_NP is used.

ESCAPE_ANY_NP is the sane choice for many cases, in particularly for

If field width is omitted the 1 byte only will be escaped.

Raw buffer as a hex string:

Raw buffer as a hex string

==========================

::

	%*ph	00 01 02  ...  3f

	%*phC	00:01:02: ... :3f

For printing a small buffers (up to 64 bytes long) as a hex string with

certain separator. For the larger buffers consider to use

	print_hex_dump().

:c:func:`print_hex_dump`.

MAC/FDDI addresses

==================

MAC/FDDI addresses:

::

	%pM	00:01:02:03:04:05

	%pMR	05:04:03:02:01:00

	%pm	000102030405

	%pmR	050403020100

	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 (':').

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

Where FDDI addresses are concerned the ``F`` specifier can be used after

the ``M`` specifier to use dash (``-``) separators instead of the default

separator.

	For Bluetooth addresses the 'R' specifier shall be used after the 'M'

For Bluetooth addresses the ``R`` specifier shall be used after the ``M``

specifier to use reversed byte order suitable for visual interpretation

of Bluetooth addresses which are in the little endian order.

Passed by reference.

IPv4 addresses:

IPv4 addresses

==============

::

	%pI4	1.2.3.4

	%pi4	001.002.003.004

	%p[Ii]4[hnbl]

	For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'

	specifiers result in a printed address with ('i4') or without ('I4')

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

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.

Passed by reference.

IPv6 addresses:

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')

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

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

Passed by reference.

IPv4/IPv6 addresses (generic, with port, flowinfo, scope):

IPv4/IPv6 addresses (generic, with port, flowinfo, scope)

=========================================================

::

	%pIS	1.2.3.4		or 0001:0002:0003:0004:0005:0006:0007:0008

	%piS	001.002.003.004	or 00010002000300040005000600070008

	%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345

	%p[Ii]S[pfschnbl]

	For printing an IP address without the need to distinguish whether it's

	of type AF_INET or AF_INET6, a pointer to a valid 'struct sockaddr',

	specified through 'IS' or 'iS', can be passed to this format specifier.

For printing an IP address without the need to distinguish whether it``s

of type AF_INET or AF_INET6, a pointer to a valid ``struct sockaddr``,

specified through ``IS`` or ``iS``, can be passed to this format specifier.

	The additional 'p', 'f', and 's' specifiers are used to specify port

	(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ':' prefix,

	flowinfo a '/' and scope a '%', each followed by the actual value.

The additional ``p``, ``f``, and ``s`` specifiers are used to specify port

(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,

flowinfo a ``/`` and scope a ``%``, each followed by the actual value.

In case of an IPv6 address the compressed IPv6 address as described by

http://tools.ietf.org/html/rfc5952 is being used if the additional

	specifier 'c' is given. The IPv6 address is surrounded by '[', ']' in

	case of additional specifiers 'p', 'f' or 's' as suggested by

specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in

case of additional specifiers ``p``, ``f`` or ``s`` as suggested by

https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07

	In case of IPv4 addresses, the additional 'h', 'n', 'b', and 'l'

In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``

specifiers can be used as well and are ignored in case of an IPv6

address.

Passed by reference.

	Further examples:

Further examples::

	%pISfc		1.2.3.4		or [1:2:3:4:5:6:7:8]/123456789

	%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890

	%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789

UUID/GUID addresses:

UUID/GUID addresses

===================

::

	%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f

	%pUB	00010203-0405-0607-0809-0A0B0C0D0E0F

Passed by reference.

dentry names:

dentry names

============

::

	%pd{,2,3,4}

	%pD{,2,3,4}

	For printing dentry name; if we race with d_move(), the name might be

	a mix of old and new ones, but it won't oops.  %pd dentry is a safer

	equivalent of %s dentry->d_name.name we used to use, %pd<n> prints

	n last components.  %pD does the same thing for struct file.

For printing dentry name; if we race with :c:func:`d_move`, the name might be

a mix of old and new ones, but it won't oops.  ``%pd`` dentry is a safer

equivalent of ``%s`` ``dentry->d_name.name`` we used to use, ``%pd<n>`` prints

``n`` last components.  ``%pD`` does the same thing for struct file.

Passed by reference.

block_device names:

block_device names

==================

::

	%pg	sda, sda1 or loop0p1

For printing name of block_device pointers.

struct va_format:

struct va_format

================

::

	%pV

For printing struct va_format structures. These contain a format string

	and va_list as follows:

and va_list as follows::

	struct va_format {

		const char *fmt;

Passed by reference.

kobjects:

kobjects

========

::

	%pO

	Base specifier for kobject based structs. Must be followed with

	Passed by reference.

struct clk:

struct clk

==========

::

	%pC	pll1

	%pCn	pll1

	%pCr	1560000000

	For printing struct clk structures. '%pC' and '%pCn' print the name

For printing struct clk structures. ``%pC`` and ``%pCn`` print the name

(Common Clock Framework) or address (legacy clock framework) of the

	structure; '%pCr' prints the current clock rate.

structure; ``%pCr`` prints the current clock rate.

Passed by reference.

bitmap and its derivatives such as cpumask and nodemask:

bitmap and its derivatives such as cpumask and nodemask

=======================================================

::

	%*pb	0779

	%*pbl	0,3-6,8-10

For printing bitmap and its derivatives such as cpumask and nodemask,

	%*pb output the bitmap with field width as the number of bits and %*pbl

``%*pb`` output the bitmap with field width as the number of bits and ``%*pbl``

output the bitmap as range list with field width as the number of bits.

Passed by reference.

Flags bitfields such as page flags, gfp_flags:

Flags bitfields such as page flags, gfp_flags

=============================================

::

	%pGp	referenced|uptodate|lru|active|private

	%pGg	GFP_USER|GFP_DMA32|GFP_NOWARN

For printing flags bitfields as a collection of symbolic constants that

would construct the value. The type of flags is given by the third

character. Currently supported are [p]age flags, [v]ma_flags (both

	expect unsigned long *) and [g]fp_flags (expects gfp_t *). The flag

expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag

names and print order depends on the particular	type.

	Note that this format should not be used directly in TP_printk() part

	of a tracepoint. Instead, use the show_*_flags() functions from

Note that this format should not be used directly in :c:func:`TP_printk()` part

of a tracepoint. Instead, use the ``show_*_flags()`` functions from

<trace/events/mmflags.h>.

Passed by reference.

Network device features:

Network device features

=======================

::

	%pNF	0x000000000000c000

Passed by reference.

If you add other %p extensions, please extend lib/test_printf.c with

If you add other ``%p`` extensions, please extend lib/test_printf.c with

one or more test cases, if at all feasible.

Thank you for your cooperation and attention.

By Randy Dunlap <rdunlap@infradead.org> and

Andrew Murray <amurray@mpc-data.co.uk>