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@@ -26,27 +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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+
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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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+
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+Pointer types
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+=============
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+
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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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+
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+Plain Pointers
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+--------------
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+
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+::
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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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+ %p abcdef12 or 00000000abcdef12
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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 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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@@ -58,6 +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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+
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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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@@ -66,14 +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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@@ -85,20 +104,33 @@ Examples::
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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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-
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Kernel Pointers
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-===============
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+---------------
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::
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- %pK 0x01234567 or 0x0123456789abcdef
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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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+
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+ %px 01234567 or 0123456789abcdef
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+
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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 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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+
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Struct Resources
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-================
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+----------------
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::
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@@ -108,32 +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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+
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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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+
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+Passed by reference.
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-DMA addresses types ``dma_addr_t``
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-==================================
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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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+
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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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@@ -143,8 +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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@@ -154,23 +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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@@ -179,12 +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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@@ -195,11 +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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@@ -209,7 +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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@@ -218,8 +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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@@ -228,7 +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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@@ -237,7 +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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@@ -247,7 +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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@@ -257,8 +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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-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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The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
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@@ -284,7 +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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UUID/GUID addresses
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-===================
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+-------------------
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::
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@@ -293,33 +330,33 @@ UUID/GUID addresses
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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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+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 notation - and big endian order in lower (b)
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+or upper case (B) hex notation.
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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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+order with lower case hex notation 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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::
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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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+For printing dentry name; if we race with :c:func:`d_move`, the name might
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+be 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 ``n``
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+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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::
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@@ -328,7 +365,7 @@ block_device names
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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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::
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@@ -350,31 +387,27 @@ 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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::
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- %pO
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+ %pOF[fnpPcCF]
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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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+For printing kobject based structs (device nodes). Default behaviour is
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+equivalent to %pOFf.
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- %pOF[fnpPcCF]
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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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- 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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+The separator when using multiple arguments is ':'
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- Examples:
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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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@@ -387,11 +420,10 @@ kobjects
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P - Populated
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B - Populated bus
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- Passed by reference.
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-
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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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::
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@@ -399,14 +431,14 @@ struct clk
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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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+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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+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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::
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@@ -414,13 +446,13 @@ bitmap and its derivatives such as cpumask and nodemask
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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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+%*pb outputs 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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::
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@@ -434,14 +466,14 @@ 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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+Note that this format should not be used directly in the
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+:c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
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+functions from <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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::
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@@ -451,8 +483,10 @@ 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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+Thanks
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+======
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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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