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printk-formats.txt: standardize document format 

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- add a title for the document;
- add markups for section titles;
- move authorship to the beginning and use :Author:;
- use right markup for tables;
- mark literals and literal blocks.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab 2017-05-16 22:27:11 -03:00 committed by Jonathan Corbet
parent 9cc07df4b5
commit 3b033380cb
1 changed files with 229 additions and 155 deletions
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384
Documentation/printk-formats.txt
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@ -1,5 +1,18 @@
If variable is of Type, use printk format specifier:
---------------------------------------------------------
=========================================
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
@ -13,25 +26,29 @@ If variable is of Type, use printk format specifier:
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
@ -41,99 +58,122 @@ Symbols/Function Pointers:
%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.
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.
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.
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:
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.
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:
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.
Passed by reference.
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
the width of the CPU data path. Passed by reference.
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,
regardless of the width of the CPU data path. Passed by reference.
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):
few examples show how the conversion would be done (the result string
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
details):
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.
The conversion rules are applied according to an optional combination
of flags (see :c:func:`string_escape_mem` kernel documentation for the
details):
ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
printing SSIDs.
- ``a`` - ESCAPE_ANY
- ``c`` - ESCAPE_SPECIAL
- ``h`` - ESCAPE_HEX
- ``n`` - ESCAPE_NULL
- ``o`` - ESCAPE_OCTAL
- ``p`` - ESCAPE_NP
- ``s`` - ESCAPE_SPACE
If field width is omitted the 1 byte only will be escaped.
By default ESCAPE_ANY_NP is used.
Raw buffer as a hex string:
ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
printing SSIDs.
If field width is omitted the 1 byte only will be escaped.
Raw buffer as a hex string
==========================
::
%*ph 00 01 02 ... 3f
%*phC 00:01:02: ... :3f
%*phD 00-01-02- ... -3f
%*phN 000102 ... 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().
For printing a small buffers (up to 64 bytes long) as a hex string with
certain separator. For the larger buffers consider to use
: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
@ -141,53 +181,62 @@ MAC/FDDI addresses:
%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
separator.
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'
specifier to use reversed byte order suitable for visual interpretation
of Bluetooth addresses which are in the little endian order.
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.
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')
leading zeros.
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.
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.
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')
colon-separators. Leading zeros are always used.
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
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.
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
@ -195,87 +244,103 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
%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
https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
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
https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
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.
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.
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
%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.
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 big endian
order with lower case hex characters will be printed.
Where no additional specifiers are used the default big endian
order with lower case hex characters will be printed.
Passed by reference.
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.
Passed by reference.
block_device names:
block_device names
==================
::
%pg sda, sda1 or loop0p1
For printing name of block_device pointers.
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:
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;
};
Implements a "recursive vsnprintf".
Implements a "recursive vsnprintf".
Do not use this feature without some mechanism to verify the
correctness of the format string and va_list arguments.
Do not use this feature without some mechanism to verify the
correctness of the format string and va_list arguments.
Passed by reference.
Passed by reference.
kobjects
========
::
kobjects:
%pO
Base specifier for kobject based structs. Must be followed with
@ -311,61 +376,70 @@ kobjects:
Passed by reference.
struct clk:
struct clk
==========
::
%pC pll1
%pCn pll1
%pCr 1560000000
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.
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.
Passed by reference.
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
output the bitmap as range list with field width as the number of bits.
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``
output the bitmap as range list with field width as the number of bits.
Passed by reference.
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
%pGv read|exec|mayread|maywrite|mayexec|denywrite
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
names and print order depends on the particular type.
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
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
<trace/events/mmflags.h>.
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.
Passed by reference.
Network device features:
Network device features
=======================
::
%pNF 0x000000000000c000
For printing netdev_features_t.
For printing netdev_features_t.
Passed by reference.
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>