484 строки
13 KiB
Plaintext
484 строки
13 KiB
Plaintext
=========================================
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How to get printk format specifiers right
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=========================================
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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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::
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If variable is of Type, use printk format specifier:
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------------------------------------------------------------
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int %d or %x
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unsigned int %u or %x
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long %ld or %lx
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unsigned long %lu or %lx
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long long %lld or %llx
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unsigned long long %llu or %llx
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size_t %zu or %zx
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ssize_t %zd or %zx
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s32 %d or %x
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u32 %u or %x
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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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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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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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unsupported specifier or length qualifier results in a WARN and early
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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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=============
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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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::
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%p abcdef12 or 00000000abcdef12
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Symbols/Function Pointers
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=========================
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::
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%pF versatile_init+0x0/0x110
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%pf versatile_init
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%pS versatile_init+0x0/0x110
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%pSR versatile_init+0x9/0x110
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(with __builtin_extract_return_addr() translation)
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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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ia64, ppc64 and parisc64 architectures where the function pointers
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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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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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Examples::
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printk("Going to call: %pF\n", gettimeofday);
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printk("Going to call: %pF\n", p->func);
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printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
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printk("%s: called from %pS\n", __func__,
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(void *)__builtin_return_address(0));
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printk("Faulted at %pS\n", (void *)regs->ip);
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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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%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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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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%px 01234567 or 0123456789abcdef
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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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Struct Resources
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================
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::
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%pr [mem 0x60000000-0x6fffffff flags 0x2200] or
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[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
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%pR [mem 0x60000000-0x6fffffff pref] or
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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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Passed by reference.
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Physical addresses 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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DMA addresses 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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Raw buffer as an escaped string
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===============================
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::
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%*pE[achnops]
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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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%*pE "\eb \C\a"\220\r]"
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%*pEhp "\x1bb \C\x07"\x90\x0d]"
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%*pEa "\e\142\040\\\103\a\042\220\r\135"
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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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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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Raw buffer as a hex string
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==========================
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::
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%*ph 00 01 02 ... 3f
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%*phC 00:01:02: ... :3f
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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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:c:func:`print_hex_dump`.
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MAC/FDDI addresses
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==================
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::
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%pM 00:01:02:03:04:05
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%pMR 05:04:03:02:01:00
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%pMF 00-01-02-03-04-05
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%pm 000102030405
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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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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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separator.
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For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
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specifier to use reversed byte order suitable for visual interpretation
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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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%pI4 1.2.3.4
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%pi4 001.002.003.004
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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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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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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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%pI6 0001:0002:0003:0004:0005:0006:0007:0008
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%pi6 00010002000300040005000600070008
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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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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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print a compressed IPv6 address as described by
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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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%pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
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%piS 001.002.003.004 or 00010002000300040005000600070008
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%pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
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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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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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specified through ``IS`` or ``iS``, can be passed to this format specifier.
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The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
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(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
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flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
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In case of an IPv6 address the compressed IPv6 address as described by
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http://tools.ietf.org/html/rfc5952 is being used if the additional
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specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
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case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
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https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
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In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
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specifiers can be used as well and are ignored in case of an IPv6
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address.
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Passed by reference.
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Further examples::
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%pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
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%pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
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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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UUID/GUID addresses
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===================
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::
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%pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
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%pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
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%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',
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'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.
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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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Passed by reference.
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dentry names
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============
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::
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%pd{,2,3,4}
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%pD{,2,3,4}
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For printing dentry name; if we race with :c:func:`d_move`, the name might be
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a mix of old and new ones, but it won't oops. ``%pd`` dentry is a safer
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equivalent of ``%s`` ``dentry->d_name.name`` we used to use, ``%pd<n>`` prints
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``n`` last components. ``%pD`` does the same thing for struct file.
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Passed by reference.
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block_device names
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==================
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::
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%pg sda, sda1 or loop0p1
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For printing name of block_device pointers.
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struct va_format
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================
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::
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%pV
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For printing struct va_format structures. These contain a format string
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and va_list as follows::
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struct va_format {
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const char *fmt;
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va_list *va;
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};
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Implements a "recursive vsnprintf".
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Do not use this feature without some mechanism to verify the
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correctness of the format string and va_list arguments.
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Passed by reference.
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kobjects
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========
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::
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%pO
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Base specifier for kobject based structs. Must be followed with
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character for specific type of kobject as listed below:
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Device tree nodes:
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%pOF[fnpPcCF]
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For printing device tree nodes. The optional arguments are:
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f device node full_name
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n device node name
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p device node phandle
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P device node path spec (name + @unit)
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F device node flags
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c major compatible string
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C full compatible string
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Without any arguments prints full_name (same as %pOFf)
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The separator when using multiple arguments is ':'
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Examples:
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%pOF /foo/bar@0 - Node full name
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%pOFf /foo/bar@0 - Same as above
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%pOFfp /foo/bar@0:10 - Node full name + phandle
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%pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
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major compatible string +
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node flags
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D - dynamic
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d - detached
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P - Populated
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B - Populated bus
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Passed by reference.
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struct clk
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==========
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::
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%pC pll1
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%pCn pll1
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%pCr 1560000000
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For printing struct clk structures. ``%pC`` and ``%pCn`` print the name
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(Common Clock Framework) or address (legacy clock framework) of the
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structure; ``%pCr`` prints the current clock rate.
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Passed by reference.
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bitmap and its derivatives such as cpumask and nodemask
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=======================================================
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::
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%*pb 0779
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%*pbl 0,3-6,8-10
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For printing bitmap and its derivatives such as cpumask and nodemask,
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``%*pb`` output the bitmap with field width as the number of bits and ``%*pbl``
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output the bitmap as range list with field width as the number of bits.
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Passed by reference.
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Flags bitfields such as page flags, gfp_flags
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=============================================
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::
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%pGp referenced|uptodate|lru|active|private
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%pGg GFP_USER|GFP_DMA32|GFP_NOWARN
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%pGv read|exec|mayread|maywrite|mayexec|denywrite
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For printing flags bitfields as a collection of symbolic constants that
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would construct the value. The type of flags is given by the third
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character. Currently supported are [p]age flags, [v]ma_flags (both
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expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
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names and print order depends on the particular type.
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Note that this format should not be used directly in :c:func:`TP_printk()` part
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of a tracepoint. Instead, use the ``show_*_flags()`` functions from
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<trace/events/mmflags.h>.
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Passed by reference.
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Network device features
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=======================
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::
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%pNF 0x000000000000c000
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For printing netdev_features_t.
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Passed by reference.
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If you add other ``%p`` extensions, please extend lib/test_printf.c with
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one or more test cases, if at all feasible.
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Thank you for your cooperation and attention.
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