forked from mirrors/linux
doc: convert printk-formats.txt to rst
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
Jonathan Corbet
parent
2a7c7cba38
commit
b3ed23213e
4 changed files with 123 additions and 114 deletions
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@ -346,8 +346,6 @@ prctl/
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- directory with info on the priveledge control subsystem
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preempt-locking.txt
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- info on locking under a preemptive kernel.
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printk-formats.txt
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- how to get printk format specifiers right
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process/
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- how to work with the mainline kernel development process.
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pps/
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@ -22,6 +22,7 @@ Core utilities
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flexible-arrays
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librs
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genalloc
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printk-formats
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Interfaces for kernel debugging
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===============================
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@ -5,6 +5,7 @@ How to get printk format specifiers right
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:Author: Randy Dunlap <rdunlap@infradead.org>
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:Author: Andrew Murray <amurray@mpc-data.co.uk>
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Integer types
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=============
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@ -25,39 +26,45 @@ Integer types
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s64 %lld or %llx
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u64 %llu or %llx
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If <type> is dependent on a config option for its size (e.g., ``sector_t``,
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``blkcnt_t``) or is architecture-dependent for its size (e.g., ``tcflag_t``),
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use a format specifier of its largest possible type and explicitly cast to it.
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If <type> is dependent on a config option for its size (e.g., sector_t,
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blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
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format specifier of its largest possible type and explicitly cast to it.
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Example::
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printk("test: sector number/total blocks: %llu/%llu\n",
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(unsigned long long)sector, (unsigned long long)blockcount);
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Reminder: ``sizeof()`` result is of type ``size_t``.
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Reminder: sizeof() returns type size_t.
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The kernel's printf does not support ``%n``. For obvious reasons, floating
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point formats (``%e, %f, %g, %a``) are also not recognized. Use of any
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The kernel's printf does not support %n. Floating point formats (%e, %f,
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%g, %a) are also not recognized, for obvious reasons. Use of any
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unsupported specifier or length qualifier results in a WARN and early
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return from vsnprintf.
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return from vsnprintf().
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Raw pointer value SHOULD be printed with %p. The kernel supports
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the following extended format specifiers for pointer types:
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Pointer Types
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Pointer types
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=============
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Pointers printed without a specifier extension (i.e unadorned %p) are
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hashed to give a unique identifier without leaking kernel addresses to user
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space. On 64 bit machines the first 32 bits are zeroed. If you _really_
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want the address see %px below.
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A raw pointer value may be printed with %p which will hash the address
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before printing. The kernel also supports extended specifiers for printing
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pointers of different types.
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Plain Pointers
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--------------
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::
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%p abcdef12 or 00000000abcdef12
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Pointers printed without a specifier extension (i.e unadorned %p) are
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hashed to prevent leaking information about the kernel memory layout. This
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has the added benefit of providing a unique identifier. On 64-bit machines
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the first 32 bits are zeroed. If you *really* want the address see %px
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below.
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Symbols/Function Pointers
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=========================
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-------------------------
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::
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@ -69,6 +76,7 @@ Symbols/Function Pointers
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%ps versatile_init
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%pB prev_fn_of_versatile_init+0x88/0x88
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The ``F`` and ``f`` specifiers are for printing function pointers,
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for example, f->func, &gettimeofday. They have the same result as
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``S`` and ``s`` specifiers. But they do an extra conversion on
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@ -77,14 +85,14 @@ are actually function descriptors.
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The ``S`` and ``s`` specifiers can be used for printing symbols
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from direct addresses, for example, __builtin_return_address(0),
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(void *)regs->ip. They result in the symbol name with (``S``) or
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without (``s``) offsets. If KALLSYMS are disabled then the symbol
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(void *)regs->ip. They result in the symbol name with (S) or
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without (s) offsets. If KALLSYMS are disabled then the symbol
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address is printed instead.
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The ``B`` specifier results in the symbol name with offsets and should be
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used when printing stack backtraces. The specifier takes into
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consideration the effect of compiler optimisations which may occur
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when tail-call``s are used and marked with the noreturn GCC attribute.
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when tail-calls are used and marked with the noreturn GCC attribute.
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Examples::
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@ -97,33 +105,32 @@ Examples::
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printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
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Kernel Pointers
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===============
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---------------
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::
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%pK 01234567 or 0123456789abcdef
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For printing kernel pointers which should be hidden from unprivileged
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users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see
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users. The behaviour of %pK depends on the kptr_restrict sysctl - see
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Documentation/sysctl/kernel.txt for more details.
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Unmodified Addresses
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====================
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--------------------
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::
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%px 01234567 or 0123456789abcdef
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For printing pointers when you _really_ want to print the address. Please
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For printing pointers when you *really* want to print the address. Please
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consider whether or not you are leaking sensitive information about the
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Kernel layout in memory before printing pointers with %px. %px is
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functionally equivalent to %lx. %px is preferred to %lx because it is more
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uniquely grep'able. If, in the future, we need to modify the way the Kernel
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handles printing pointers it will be nice to be able to find the call
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sites.
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kernel memory layout before printing pointers with %px. %px is functionally
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equivalent to %lx (or %lu). %px is preferred because it is more uniquely
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grep'able. If in the future we need to modify the way the kernel handles
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printing pointers we will be better equipped to find the call sites.
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Struct Resources
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================
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----------------
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::
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@ -133,32 +140,37 @@ Struct Resources
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[mem 0x0000000060000000-0x000000006fffffff pref]
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For printing struct resources. The ``R`` and ``r`` specifiers result in a
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printed resource with (``R``) or without (``r``) a decoded flags member.
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printed resource with (R) or without (r) a decoded flags member.
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Passed by reference.
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Physical addresses types ``phys_addr_t``
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========================================
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Physical address types phys_addr_t
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----------------------------------
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::
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%pa[p] 0x01234567 or 0x0123456789abcdef
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For printing a ``phys_addr_t`` type (and its derivatives, such as
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``resource_size_t``) which can vary based on build options, regardless of
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the width of the CPU data path. Passed by reference.
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For printing a phys_addr_t type (and its derivatives, such as
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resource_size_t) which can vary based on build options, regardless of the
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width of the CPU data path.
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DMA addresses types ``dma_addr_t``
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==================================
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Passed by reference.
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DMA address types dma_addr_t
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----------------------------
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::
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%pad 0x01234567 or 0x0123456789abcdef
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For printing a ``dma_addr_t`` type which can vary based on build options,
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regardless of the width of the CPU data path. Passed by reference.
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For printing a dma_addr_t type which can vary based on build options,
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regardless of the width of the CPU data path.
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Passed by reference.
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Raw buffer as an escaped string
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===============================
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-------------------------------
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::
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@ -168,8 +180,8 @@ For printing raw buffer as an escaped string. For the following buffer::
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1b 62 20 5c 43 07 22 90 0d 5d
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few examples show how the conversion would be done (the result string
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without surrounding quotes)::
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A few examples show how the conversion would be done (excluding surrounding
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quotes)::
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%*pE "\eb \C\a"\220\r]"
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%*pEhp "\x1bb \C\x07"\x90\x0d]"
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@ -179,23 +191,23 @@ The conversion rules are applied according to an optional combination
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of flags (see :c:func:`string_escape_mem` kernel documentation for the
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details):
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- ``a`` - ESCAPE_ANY
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- ``c`` - ESCAPE_SPECIAL
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- ``h`` - ESCAPE_HEX
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- ``n`` - ESCAPE_NULL
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- ``o`` - ESCAPE_OCTAL
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- ``p`` - ESCAPE_NP
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- ``s`` - ESCAPE_SPACE
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- a - ESCAPE_ANY
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- c - ESCAPE_SPECIAL
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- h - ESCAPE_HEX
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- n - ESCAPE_NULL
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- o - ESCAPE_OCTAL
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- p - ESCAPE_NP
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- s - ESCAPE_SPACE
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By default ESCAPE_ANY_NP is used.
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ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
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printing SSIDs.
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If field width is omitted the 1 byte only will be escaped.
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If field width is omitted then 1 byte only will be escaped.
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Raw buffer as a hex string
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==========================
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--------------------------
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::
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@ -204,12 +216,12 @@ Raw buffer as a hex string
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%*phD 00-01-02- ... -3f
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%*phN 000102 ... 3f
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For printing a small buffers (up to 64 bytes long) as a hex string with
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certain separator. For the larger buffers consider to use
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For printing small buffers (up to 64 bytes long) as a hex string with a
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certain separator. For larger buffers consider using
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:c:func:`print_hex_dump`.
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MAC/FDDI addresses
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==================
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------------------
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::
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@ -220,11 +232,11 @@ MAC/FDDI addresses
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%pmR 050403020100
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For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
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specifiers result in a printed address with (``M``) or without (``m``) byte
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separators. The default byte separator is the colon (``:``).
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specifiers result in a printed address with (M) or without (m) byte
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separators. The default byte separator is the colon (:).
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Where FDDI addresses are concerned the ``F`` specifier can be used after
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the ``M`` specifier to use dash (``-``) separators instead of the default
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the ``M`` specifier to use dash (-) separators instead of the default
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separator.
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For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
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@ -234,7 +246,7 @@ of Bluetooth addresses which are in the little endian order.
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Passed by reference.
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IPv4 addresses
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==============
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--------------
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::
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@ -243,8 +255,8 @@ IPv4 addresses
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%p[Ii]4[hnbl]
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For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
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specifiers result in a printed address with (``i4``) or without (``I4``)
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leading zeros.
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specifiers result in a printed address with (i4) or without (I4) leading
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zeros.
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The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
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host, network, big or little endian order addresses respectively. Where
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@ -253,7 +265,7 @@ no specifier is provided the default network/big endian order is used.
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Passed by reference.
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IPv6 addresses
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==============
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--------------
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::
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@ -262,7 +274,7 @@ IPv6 addresses
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%pI6c 1:2:3:4:5:6:7:8
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For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
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specifiers result in a printed address with (``I6``) or without (``i6``)
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specifiers result in a printed address with (I6) or without (i6)
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colon-separators. Leading zeros are always used.
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The additional ``c`` specifier can be used with the ``I`` specifier to
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|
|
@ -272,7 +284,7 @@ http://tools.ietf.org/html/rfc5952
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Passed by reference.
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IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
|
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=========================================================
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---------------------------------------------------------
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|
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::
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@ -282,8 +294,8 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
|
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%pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
|
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%p[Ii]S[pfschnbl]
|
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|
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For printing an IP address without the need to distinguish whether it``s
|
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of type AF_INET or AF_INET6, a pointer to a valid ``struct sockaddr``,
|
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For printing an IP address without the need to distinguish whether it's of
|
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type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
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specified through ``IS`` or ``iS``, can be passed to this format specifier.
|
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|
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The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
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|
@ -309,7 +321,7 @@ Further examples::
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%pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
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|
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UUID/GUID addresses
|
||||
===================
|
||||
-------------------
|
||||
|
||||
::
|
||||
|
||||
|
|
@ -318,33 +330,33 @@ UUID/GUID addresses
|
|||
%pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
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%pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
|
||||
|
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For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
|
||||
'b' and 'B' specifiers are used to specify a little endian order in
|
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lower ('l') or upper case ('L') hex characters - and big endian order
|
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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
|
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order with lower case hex characters will be printed.
|
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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.
|
||||
|
|
@ -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
|
||||
|
|
|
|||
Loading…
Reference in a new issue