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doc: convert printk-formats.txt to rst

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Documentation/printk-formats.txt is a candidate for conversion to
ReStructuredText format. Some effort has already been made to do this
conversion even thought the suffix is currently .txt

Changes required to complete conversion

 - Move printk-formats.txt to core-api/printk-formats.rst
 - Add entry to Documentation/core-api/index.rst
 - Remove entry from Documentation/00-INDEX
 - Fix minor grammatical errors.
 - Order heading adornments as suggested by rst docs.
 - Use 'Passed by reference' uniformly.
 - Update pointer documentation around %px specifier.
 - Fix erroneous double backticks (to commas).
 - Remove extraneous double backticks (suggested by Jonathan Corbet).
 - Simplify documentation for kobject.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
[jc: downcased "kernel"]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Tobin C. Harding 2017-12-20 08:17:15 +11:00 committed by Jonathan Corbet
parent 2a7c7cba38
commit b3ed23213e
4 changed files with 123 additions and 114 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
Documentation/00-INDEX
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@ -346,8 +346,6 @@ prctl/
- directory with info on the priveledge control subsystem
preempt-locking.txt
- info on locking under a preemptive kernel.
printk-formats.txt
- how to get printk format specifiers right
process/
- how to work with the mainline kernel development process.
pps/

1
Documentation/core-api/index.rst
View file

@ -22,6 +22,7 @@ Core utilities
flexible-arrays
librs
genalloc
printk-formats
Interfaces for kernel debugging
===============================

231
Documentation/printk-formats.txt → Documentation/core-api/printk-formats.rst
View file

@ -5,6 +5,7 @@ How to get printk format specifiers right
:Author: Randy Dunlap <rdunlap@infradead.org>
:Author: Andrew Murray <amurray@mpc-data.co.uk>
Integer types
=============
@ -25,39 +26,45 @@ Integer types
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.
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() returns 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. Floating point formats (%e, %f,
%g, %a) are also not recognized, for obvious reasons. Use of any
unsupported specifier or length qualifier results in a WARN and early
return from vsnprintf.
return from vsnprintf().
Raw pointer value SHOULD be printed with %p. The kernel supports
the following extended format specifiers for pointer types:
Pointer Types
Pointer types
=============
Pointers printed without a specifier extension (i.e unadorned %p) are
hashed to give a unique identifier without leaking kernel addresses to user
space. On 64 bit machines the first 32 bits are zeroed. If you _really_
want the address see %px below.
A raw pointer value may be printed with %p which will hash the address
before printing. The kernel also supports extended specifiers for printing
pointers of different types.
Plain Pointers
--------------
::
%p abcdef12 or 00000000abcdef12
Pointers printed without a specifier extension (i.e unadorned %p) are
hashed to prevent leaking information about the kernel memory layout. This
has the added benefit of providing a unique identifier. On 64-bit machines
the first 32 bits are zeroed. If you *really* want the address see %px
below.
Symbols/Function Pointers
=========================
-------------------------
::
@ -69,6 +76,7 @@ Symbols/Function Pointers
%ps versatile_init
%pB prev_fn_of_versatile_init+0x88/0x88
The ``F`` and ``f`` specifiers are for printing function pointers,
for example, f->func, &gettimeofday. They have the same result as
``S`` and ``s`` specifiers. But they do an extra conversion on
@ -77,14 +85,14 @@ are actually function descriptors.
The ``S`` and ``s`` specifiers can be used for printing symbols
from direct addresses, for example, __builtin_return_address(0),
(void *)regs->ip. They result in the symbol name with (``S``) or
without (``s``) offsets. If KALLSYMS are disabled then the symbol
(void *)regs->ip. They result in the symbol name with (S) or
without (s) offsets. If KALLSYMS are disabled then 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.
when tail-calls are used and marked with the noreturn GCC attribute.
Examples::
@ -97,33 +105,32 @@ Examples::
printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
Kernel Pointers
===============
---------------
::
%pK 01234567 or 0123456789abcdef
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.
Unmodified Addresses
====================
--------------------
::
%px 01234567 or 0123456789abcdef
For printing pointers when you _really_ want to print the address. Please
For printing pointers when you *really* want to print the address. Please
consider whether or not you are leaking sensitive information about the
Kernel layout in memory before printing pointers with %px. %px is
functionally equivalent to %lx. %px is preferred to %lx because it is more
uniquely grep'able. If, in the future, we need to modify the way the Kernel
handles printing pointers it will be nice to be able to find the call
sites.
kernel memory layout before printing pointers with %px. %px is functionally
equivalent to %lx (or %lu). %px is preferred because it is more uniquely
grep'able. If in the future we need to modify the way the kernel handles
printing pointers we will be better equipped to find the call sites.
Struct Resources
================
----------------
::
@ -133,32 +140,37 @@ Struct Resources
[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.
printed resource with (R) or without (r) a decoded flags member.
Passed by reference.
Physical addresses types ``phys_addr_t``
========================================
Physical address 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.
DMA addresses types ``dma_addr_t``
==================================
Passed by reference.
DMA address 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
===============================
-------------------------------
::
@ -168,8 +180,8 @@ 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)::
A few examples show how the conversion would be done (excluding surrounding
quotes)::
%*pE "\eb \C\a"\220\r]"
%*pEhp "\x1bb \C\x07"\x90\x0d]"
@ -179,23 +191,23 @@ The conversion rules are applied according to an optional combination
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
printing SSIDs.
If field width is omitted the 1 byte only will be escaped.
If field width is omitted then 1 byte only will be escaped.
Raw buffer as a hex string
==========================
--------------------------
::
@ -204,12 +216,12 @@ Raw buffer as a hex string
%*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
For printing small buffers (up to 64 bytes long) as a hex string with a
certain separator. For larger buffers consider using
:c:func:`print_hex_dump`.
MAC/FDDI addresses
==================
------------------
::
@ -220,11 +232,11 @@ MAC/FDDI addresses
%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 (``:``).
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
the ``M`` specifier to use dash (-) separators instead of the default
separator.
For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
@ -234,7 +246,7 @@ of Bluetooth addresses which are in the little endian order.
Passed by reference.
IPv4 addresses
==============
--------------
::
@ -243,8 +255,8 @@ IPv4 addresses
%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.
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
@ -253,7 +265,7 @@ no specifier is provided the default network/big endian order is used.
Passed by reference.
IPv6 addresses
==============
--------------
::
@ -262,7 +274,7 @@ IPv6 addresses
%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``)
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
@ -272,7 +284,7 @@ http://tools.ietf.org/html/rfc5952
Passed by reference.
IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
=========================================================
---------------------------------------------------------
::
@ -282,8 +294,8 @@ 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``,
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
@ -309,7 +321,7 @@ Further examples::
%pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
UUID/GUID addresses
===================
-------------------
::
@ -318,33 +330,33 @@ UUID/GUID addresses
%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 notation - and big endian order in lower (b)
or upper case (B) hex notation.
Where no additional specifiers are used the default big endian
order with lower case hex characters will be printed.
order with lower case hex notation will be printed.
Passed by reference.
dentry names
============
------------
::
%pd{,2,3,4}
%pD{,2,3,4}
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.
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
==================
------------------
::
@ -353,7 +365,7 @@ block_device names
For printing name of block_device pointers.
struct va_format
================
----------------
::
@ -375,31 +387,27 @@ correctness of the format string and va_list arguments.
Passed by reference.
kobjects
========
--------
::
%pO
Base specifier for kobject based structs. Must be followed with
character for specific type of kobject as listed below:
Device tree nodes:
%pOF[fnpPcCF]
For printing device tree nodes. The optional arguments are:
f device node full_name
n device node name
p device node phandle
P device node path spec (name + @unit)
F device node flags
c major compatible string
C full compatible string
Without any arguments prints full_name (same as %pOFf)
The separator when using multiple arguments is ':'
Examples:
For printing kobject based structs (device nodes). Default behaviour is
equivalent to %pOFf.
- f - device node full_name
- n - device node name
- p - device node phandle
- P - device node path spec (name + @unit)
- F - device node flags
- c - major compatible string
- C - full compatible string
The separator when using multiple arguments is ':'
Examples::
%pOF /foo/bar@0 - Node full name
%pOFf /foo/bar@0 - Same as above
@ -412,11 +420,10 @@ kobjects
P - Populated
B - Populated bus
Passed by reference.
Passed by reference.
struct clk
==========
----------
::
@ -424,14 +431,14 @@ struct clk
%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
=======================================================
-------------------------------------------------------
::
@ -439,13 +446,13 @@ bitmap and its derivatives such as cpumask and nodemask
%*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 outputs 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
=============================================
---------------------------------------------
::
@ -459,14 +466,14 @@ 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 :c:func:`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 the
: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
=======================
-----------------------
::
@ -476,8 +483,10 @@ For printing netdev_features_t.
Passed by reference.
If you add other ``%p`` extensions, please extend lib/test_printf.c with
Thanks
======
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.

3
lib/vsprintf.c
View file

@ -1834,7 +1834,8 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
*
* - 'x' For printing the address. Equivalent to "%lx".
*
* ** Please update also Documentation/printk-formats.txt when making changes **
* ** When making changes please also update:
* Documentation/core-api/printk-formats.rst
*
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a