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Date:   Wed, 6 Dec 2017 10:18:49 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Tobin C. Harding" <me@...in.cc>, Jonathan Corbet <corbet@....net>
Cc:     Andrew Murray <amurray@...-data.co.uk>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] doc: convert printk-formats.txt to rst

On 12/05/2017 05:45 PM, Tobin C. Harding wrote:
> 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
> 
> - Add double backticks where needed.
> - Add entry to Documentation/index.rst
> - Use flat-table instead of ASCII table.
> - Fix minor grammatical errors.
> - Capitalize headers and correctly order heading adornments.

That's a style choice and an unneeded change (referring to Capitalize headers).

> - Use 'Passed by reference' uniformly.
> - Update pointer documentation around %px specifier.
> - Fix erroneous double backticks (to commas).
> - Simplify documentation for kobject.
> - Convert lib/vsnprintf.c function docs to use kernel-docs and
>   include in Documentation/printk-formats.rst

good idea.

> 
> Signed-off-by: Tobin C. Harding <me@...in.cc>
> ---
> 
> The last two need special reviewing please. In particular the conversion
> of kernel-docs in vsnprintf.c attempt was made to reduce documentation
> duplication with comments in the source code being simplified in order
> to be suitable for inclusion in Documentation/printk-formats.rst
> 
> I used -M when formatting the patch. If you don't like the diff with
> this flag just holla.
> 
> thanks,
> Tobin.
> 
>  Documentation/index.rst                            |  10 +
>  .../{printk-formats.txt => printk-formats.rst}     | 295 ++++++++++++---------
>  lib/vsprintf.c                                     | 160 +++++------
>  3 files changed, 235 insertions(+), 230 deletions(-)
>  rename Documentation/{printk-formats.txt => printk-formats.rst} (61%)

> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.rst
> similarity index 61%
> rename from Documentation/printk-formats.txt
> rename to Documentation/printk-formats.rst
> index aa0a776c817a..51449d213748 100644
> --- a/Documentation/printk-formats.txt
> +++ b/Documentation/printk-formats.rst
> @@ -1,6 +1,6 @@
> -=========================================
> -How to get printk format specifiers right
> -=========================================
> +=============================================
> +How to Get ``printk`` Format Specifiers Right
> +=============================================
>  
>  :Author: Randy Dunlap <rdunlap@...radead.org>
>  :Author: Andrew Murray <amurray@...-data.co.uk>
> @@ -8,56 +8,91 @@ How to get printk format specifiers right
>  Integer types
>  =============
>  
> -::
> +For printing integer types, we have the following format specifiers:
> +		
> +   .. flat-table:: 
> +      :widths: 2 2
> +
> +      * - **Type**
> +	- **Specifier**
> +
> +      * - ``int``
> +        - ``%d`` or ``%x``
> +
> +      * - ``unsigned int``
> +	- ``%u`` or ``%x``
> +
> +      * - ``long``
> +	- ``%ld`` or ``%lx``
> +
> +      * - ``unsigned long``
> +	- ``%lu`` or ``%lx``
> +
> +      * - ``long long``
> +	- ``%lld`` or ``%llx``
>  
> -	If variable is of Type,		use printk format specifier:
> -	------------------------------------------------------------
> -		int			%d or %x
> -		unsigned int		%u or %x
> -		long			%ld or %lx
> -		unsigned long		%lu or %lx
> -		long long		%lld or %llx
> -		unsigned long long	%llu or %llx
> -		size_t			%zu or %zx
> -		ssize_t			%zd or %zx
> -		s32			%d or %x
> -		u32			%u or %x
> -		s64			%lld or %llx
> -		u64			%llu or %llx
> -
> -If <type> is dependent on a config option for its size (e.g., ``sector_t``,
> +      * - ``unsigned long long``
> +	- ``%llu`` or ``%llx``
> +
> +      * - ``size_t``
> +	- ``%zu`` or ``%zx``
> +
> +      * - ``ssize_t``
> +	- ``%zd`` or ``%zx``
> +
> +      * - ``s32``
> +	- ``%d`` or ``%x``
> +
> +      * - ``u32``
> +	- ``%u`` or ``%x``
> +
> +      * - ``s64``
> +	- ``%lld`` or ``%llx``
> +
> +      * - ``u64``
> +	- ``%llu`` or ``%llx``
> +
> +
> +If ``<type>`` is dependent on a config option for its size (e.g., ``sector_t``,
>  ``blkcnt_t``) or is architecture-dependent for its size (e.g., ``tcflag_t``),
>  use a format specifier of its largest possible type and explicitly cast to it.
>  
>  Example::
>  
> -	printk("test: sector number/total blocks: %llu/%llu\n",
> -		(unsigned long long)sector, (unsigned long long)blockcount);
> +	printk("test: total blocks: %llu\n", (unsigned long long)blockcount);
>  
> -Reminder: ``sizeof()`` result is of type ``size_t``.
> +Reminder: ``sizeof()`` returns type ``size_t``.
>  
> -The kernel's printf does not support ``%n``. For obvious reasons, floating
> +The kernel's printf does not support ``%n``. For obvious reasons floating
>  point formats (``%e, %f, %g, %a``) are also not recognized. Use of any
>  unsupported specifier or length qualifier results in a WARN and early
> -return from vsnprintf.
> -
> -Raw pointer value SHOULD be printed with %p. The kernel supports
> -the following extended format specifiers for pointer types:
> +return from ``vsnprintf()``.
>  
>  Pointer Types
>  =============
>  
> -Pointers printed without a specifier extension (i.e unadorned %p) are
> -hashed to give a unique identifier without leaking kernel addresses to user
> -space. On 64 bit machines the first 32 bits are zeroed. If you _really_
> -want the address see %px below.
> +A raw pointer value may be printed with ``%p`` which will hash the address
> +before printing. The Kernel also supports extended specifiers for printing
> +pointers of different types.
> +
> +.. kernel-doc:: lib/vsprintf.c
> +     :doc: Extended Format Pointer Specifiers
> +
> +
> +Plain Pointers
> +--------------
>  
>  ::
>  
>  	%p	abcdef12 or 00000000abcdef12
>  
> +Pointers printed without a specifier extension (i.e unadorned ``%p``) are
> +hashed to give a unique identifier without leaking kernel addresses to user
> +space. On 64 bit machines the first 32 bits are zeroed. If you *really*

             64-bit

> +want the address see ``%px`` below.
> +
>  Symbols/Function Pointers
> -=========================
> +-------------------------
>  
>  ::
>  
> @@ -69,61 +104,60 @@ Symbols/Function Pointers
>  	%ps	versatile_init
>  	%pB	prev_fn_of_versatile_init+0x88/0x88
>  
> -The ``F`` and ``f`` specifiers are for printing function pointers,
> -for example, f->func, &gettimeofday. They have the same result as
> -``S`` and ``s`` specifiers. But they do an extra conversion on
> -ia64, ppc64 and parisc64 architectures where the function pointers
> -are actually function descriptors.
> +The ``F`` and ``f`` specifiers are for printing function pointers, for
> +example, ``f->func``, ``&gettimeofday``. They have the same result as ``S``
> +and ``s`` specifiers. But they do an extra conversion on ia64, ppc64 and
> +parisc64 architectures where the function pointers are actually function
> +descriptors.
>  
>  The ``S`` and ``s`` specifiers can be used for printing symbols
> -from direct addresses, for example, __builtin_return_address(0),
> -(void *)regs->ip. They result in the symbol name with (``S``) or
> +from direct addresses, for example, ``__builtin_return_address(0)``,
> +``(void *)regs->ip``. They result in the symbol name with (``S``) or
>  without (``s``) offsets. If KALLSYMS are disabled then the symbol
>  address is printed instead.
>  
>  The ``B`` specifier results in the symbol name with offsets and should be
>  used when printing stack backtraces. The specifier takes into
>  consideration the effect of compiler optimisations which may occur
> -when tail-call``s are used and marked with the noreturn GCC attribute.
> +when tail-call's are used and marked with the ``noreturn`` GCC attribute.
>  
>  Examples::
>  
>  	printk("Going to call: %pF\n", gettimeofday);
>  	printk("Going to call: %pF\n", p->func);
>  	printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
> -	printk("%s: called from %pS\n", __func__,
> -				(void *)__builtin_return_address(0));
> +	printk("%s: called from %pS\n", __func__, (void *)__builtin_return_address(0));
>  	printk("Faulted at %pS\n", (void *)regs->ip);
>  	printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
>  
>  Kernel Pointers
> -===============
> +---------------
>  
>  ::
>  
>  	%pK	01234567 or 0123456789abcdef
>  
>  For printing kernel pointers which should be hidden from unprivileged
> -users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see
> -Documentation/sysctl/kernel.txt for more details.
> +users. The behaviour of ``%pK`` depends on the ``kptr_restrict`` sysctl -
> +see ``Documentation/sysctl/kernel.txt`` for more details.
>  
>  Unmodified Addresses
> -====================
> +--------------------
>  
>  ::
>  
>  	%px	01234567 or 0123456789abcdef
>  
> -For printing pointers when you _really_ want to print the address. Please
> +For printing pointers when you *really* want to print the address. Please
>  consider whether or not you are leaking sensitive information about the
> -Kernel layout in memory before printing pointers with %px. %px is
> -functionally equivalent to %lx. %px is preferred to %lx because it is more
> -uniquely grep'able. If, in the future, we need to modify the way the Kernel
> -handles printing pointers it will be nice to be able to find the call
> -sites.
> +kernel memory layout before printing pointers with ``%px``. ``%px`` is
> +functionally equivalent to ``%lx`` (or ``%lu``). ``%px``, however, is
> +preferable because it is more uniquely grep'able. If, in the future, we need
> +to modify the way the Kernel handles printing pointers we will be better
> +equipped to find the call sites.
>  
>  Struct Resources
> -================
> +----------------
>  
>  ::
>  
> @@ -132,12 +166,13 @@ Struct Resources
>  	%pR	[mem 0x60000000-0x6fffffff pref] or
>  		[mem 0x0000000060000000-0x000000006fffffff pref]
>  
> -For printing struct resources. The ``R`` and ``r`` specifiers result in a
> +For printing ``struct resources``. The ``R`` and ``r`` specifiers result in a
>  printed resource with (``R``) or without (``r``) a decoded flags member.
> +
>  Passed by reference.
>  
> -Physical addresses types ``phys_addr_t``
> -========================================
> +Physical Address Types ``phys_addr_t``
> +--------------------------------------
>  
>  ::
>  
> @@ -145,20 +180,24 @@ Physical addresses types ``phys_addr_t``
>  
>  For printing a ``phys_addr_t`` type (and its derivatives, such as
>  ``resource_size_t``) which can vary based on build options, regardless of
> -the width of the CPU data path. Passed by reference.
> +the width of the CPU data path.
> +
> +Passed by reference.
>  
> -DMA addresses types ``dma_addr_t``
> -==================================
> +DMA Address Types ``dma_addr_t``
> +--------------------------------
>  
>  ::
>  
>  	%pad	0x01234567 or 0x0123456789abcdef
>  
>  For printing a ``dma_addr_t`` type which can vary based on build options,
> -regardless of the width of the CPU data path. Passed by reference.
> +regardless of the width of the CPU data path.
>  
> -Raw buffer as an escaped string
> -===============================
> +Passed by reference.
> +
> +Raw Buffer as an Escaped String
> +-------------------------------
>  
>  ::
>  
> @@ -168,7 +207,7 @@ For printing raw buffer as an escaped string. For the following buffer::
>  
>  		1b 62 20 5c 43 07 22 90 0d 5d
>  
> -few examples show how the conversion would be done (the result string
> +A few examples show how the conversion would be done (the result string
>  without surrounding quotes)::
>  
>  		%*pE		"\eb \C\a"\220\r]"
> @@ -194,8 +233,8 @@ printing SSIDs.
>  
>  If field width is omitted the 1 byte only will be escaped.

                             then
I think...

>  
> -Raw buffer as a hex string
> -==========================
> +Raw Buffer as a Hex String
> +--------------------------
>  
>  ::
>  
> @@ -205,11 +244,11 @@ Raw buffer as a hex string
>  	%*phN	000102 ... 3f
>  
>  For printing a small buffers (up to 64 bytes long) as a hex string with
> -certain separator. For the larger buffers consider to use
> +certain separator. For the larger buffers consider using
>  :c:func:`print_hex_dump`.
>  
> -MAC/FDDI addresses
> -==================
> +MAC/FDDI Addresses
> +------------------
>  
>  ::
>  
> @@ -233,8 +272,8 @@ of Bluetooth addresses which are in the little endian order.
>  
>  Passed by reference.
>  
> -IPv4 addresses
> -==============
> +IPv4 Addresses
> +--------------
>  
>  ::
>  
> @@ -252,8 +291,8 @@ no specifier is provided the default network/big endian order is used.
>  
>  Passed by reference.
>  
> -IPv6 addresses
> -==============
> +IPv6 Addresses
> +--------------
>  
>  ::
>  
> @@ -271,8 +310,8 @@ http://tools.ietf.org/html/rfc5952
>  
>  Passed by reference.
>  
> -IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
> -=========================================================
> +IPv4/IPv6 Addresses (generic, with port, flowinfo or scope)
> +---------------------------------------------------------------

I prefer the additional (Oxford) comma.
and why is the --- line longer than the header?

>  
>  ::
>  
> @@ -282,8 +321,8 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
>  	%pISpc	1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345
>  	%p[Ii]S[pfschnbl]
>  
> -For printing an IP address without the need to distinguish whether it``s
> -of type AF_INET or AF_INET6, a pointer to a valid ``struct sockaddr``,
> +For printing an IP address without the need to distinguish whether it's
> +of type AF_INET or AF_INET6. A pointer to a valid ``struct sockaddr``,
>  specified through ``IS`` or ``iS``, can be passed to this format specifier.
>  
>  The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
> @@ -308,8 +347,8 @@ Further examples::
>  	%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
>  	%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
>  
> -UUID/GUID addresses
> -===================
> +UUID/GUID Addresses
> +-------------------
>  
>  ::
>  
> @@ -318,18 +357,18 @@ UUID/GUID addresses
>  	%pUl	03020100-0504-0706-0809-0a0b0c0e0e0f
>  	%pUL	03020100-0504-0706-0809-0A0B0C0E0E0F
>  
> -For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
> -'b' and 'B' specifiers are used to specify a little endian order in
> -lower ('l') or upper case ('L') hex characters - and big endian order
> -in lower ('b') or upper case ('B') hex characters.
> +For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
> +``b`` and ``B`` specifiers are used to specify a little endian order in
> +lower (``l``) or upper case (``L``) hex digits - and big endian order
> +in lower (``b``) or upper case (``B``) hex digits.
>  
>  Where no additional specifiers are used the default big endian
> -order with lower case hex characters will be printed.
> +order with lower case hex digits will be printed.

digits could imply base 10. but no big deal.

>  
>  Passed by reference.
>  
> -dentry names
> -============
> +Dentry Names
> +------------
>  
>  ::
>  
> @@ -343,24 +382,24 @@ equivalent of ``%s`` ``dentry->d_name.name`` we used to use, ``%pd<n>`` prints
>  
>  Passed by reference.
>  
> -block_device names
> -==================
> +block_device Names
> +------------------
>  
>  ::
>  
>  	%pg	sda, sda1 or loop0p1
>  
> -For printing name of block_device pointers.
> +For printing name of ``block_device`` pointers.
>  
>  struct va_format
> -================
> +----------------
>  
>  ::
>  
>  	%pV
>  
> -For printing struct va_format structures. These contain a format string
> -and va_list as follows::
> +For printing ``struct va_format`` structures. These contain a format string
> +and ``va_list`` as follows::
>  
>  	struct va_format {
>  		const char *fmt;
> @@ -370,36 +409,33 @@ and va_list as follows::
>  Implements a "recursive vsnprintf".
>  
>  Do not use this feature without some mechanism to verify the
> -correctness of the format string and va_list arguments.
> +correctness of the format string and ``va_list`` arguments.
>  
>  Passed by reference.
>  
>  kobjects
> -========
> -
> +--------
> +	
>  ::
>  
> -	%pO
> +	%pOF[fnpPcCF]
>  
> -	Base specifier for kobject based structs. Must be followed with
> -	character for specific type of kobject as listed below:
>  
> -	Device tree nodes:
> +For printing kobject based structs (device nodes). Default behaviour is
> +equivalent to ``%pOFf``.
>  
> -	%pOF[fnpPcCF]
> +	- ``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
>  
> -	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 ':'
> +The separator when using multiple arguments is ``:``
>  
> -	Examples:
> +Examples:
> +::
>  
>  	%pOF	/foo/bar@0			- Node full name
>  	%pOFf	/foo/bar@0			- Same as above
> @@ -412,11 +448,10 @@ kobjects
>  							P - Populated
>  							B - Populated bus
>  
> -	Passed by reference.
> -
> +Passed by reference.
>  
>  struct clk
> -==========
> +----------
>  
>  ::
>  
> @@ -424,14 +459,14 @@ 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.
>  
>  Passed by reference.
>  
> -bitmap and its derivatives such as cpumask and nodemask
> -=======================================================
> +Bitmap and its Derivatives (such as cpumask and nodemask)
> +---------------------------------------------------------
>  
>  ::
>  
> @@ -439,13 +474,13 @@ 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``
> -output the bitmap as range list with field width as the number of bits.
> +``%*pb`` outputs the bitmap with field width as the number of bits and ``%*pbl``
> +outputs the bitmap as range list with field width as the number of bits.
>  
>  Passed by reference.
>  
> -Flags bitfields such as page flags, gfp_flags
> -=============================================
> +Flags Bitfields (such as page flags, gfp_flags)
> +-----------------------------------------------
>  
>  ::
>  
> @@ -459,25 +494,27 @@ 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
> -=======================
> +Network Device Features
> +-----------------------
>  
>  ::
>  
>  	%pNF	0x000000000000c000
>  
> -For printing netdev_features_t.
> +For printing ``netdev_features_t``.
>  
>  Passed by reference.
>  
> -If you add other ``%p`` extensions, please extend lib/test_printf.c with
> -one or more test cases, if at all feasible.
> +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.
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 01c3957b2de6..f9247b78e8ef 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1727,115 +1727,73 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
>  	return number(buf, end, hashval, spec);
>  }
>  
> +/**
> + * DOC: Extended Format Pointer Specifiers
> + *
> + * Briefly we handle the following extensions:
> + *
> + * - ``F`` - For symbolic function descriptor pointers with offset.
> + * - ``f`` - For simple symbolic function names without offset.
> + *
> + * - ``S`` - For symbolic direct pointers with offset.
> + * - ``s`` - For symbolic direct pointers without offset.
> + * - ``[FfSs]R`` - As above with ``__builtin_extract_return_addr()`` translation.
> + * - ``B`` - For backtraced symbolic direct pointers with offset.
> + * - ``R`` - For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref].
> + * - ``r`` - For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201].
> + * - ``b[l]`` - For a bitmap, the number of bits is determined by the field
> + *   width which must be explicitly specified either as part of the format
> + *   string ``32b[l]`` or through ``*b[l]``, ``[l]`` selects range-list format
> + *   instead of hex format.
> + * - ``M`` - For a 6-byte MAC address, it prints the address in the usual
> + *   colon-separated hex notation.
> + * - ``m`` - For a 6-byte MAC address, it prints the hex address without colons.
> + * - ``MF`` - For a 6-byte MAC FDDI address, it prints the address with a
> + *   dash-separated hex notation.
> + * - ``[mM]R`` - For a 6-byte MAC address, Reverse order (Bluetooth).
> + * - ``I[46]`` - For IPv4/IPv6 addresses printed in the usual way.
> + * - ``I[S][pfs]`` - For generic IPv4/IPv6 address (struct sockaddr *) that falls
> + *   back to ``[4]`` or ``[6]`` and is able to print port ``[p]``,
> + *   flowinfo ``[f]``, scope ``[s]``.
> + * - ``i[46]`` - For 'raw' IPv4/IPv6 addresses IPv6 omits the colons (01020304...0f)
> + *   IPv4 uses dot-separated decimal with leading 0's (010.123.045.006).
> + * - ``i[S][pfs]`` - For generic IPv4/IPv6 address (struct sockaddr *) that falls back
> + *   to ``[4]`` or ``[6]`` (``[pfs]`` as above).
> + * - ``[Ii][4S][hnbl]`` - For IPv4 addresses in host, network, big or little endian order.
> + * - ``I[6S]c`` - For IPv6 addresses printed as per http://tools.ietf.org/html/rfc5952.
> + * - ``E[achnops]`` - For an escaped buffer.
> + * - ``U`` - For a 16 byte UUID/GUID.
> + * - ``V`` - For a ``struct va_format`` which contains a format ``string *``
> + *   and ``va_list *``.
> + * - ``K`` -  For a kernel pointer that should be hidden from unprivileged users.
> + * - ``NF`` - For a ``netdev_features_t``.
> + * - ``h[CDN]`` - For a variable-length buffer.
> + * - ``a[pd]`` - For address types ``[p] phys_addr_t``, ``[d] dma_addr_t`` and
> + *   derivatives.
> + * - ``d[234]`` - For a dentry name (optionally 2-4 last components).
> + * - ``D[234]`` - Same as 'd' but for a struct file.
> + * - ``g`` - For ``block_device`` name (gendisk + partition number).
> + * - ``C[n]`` - For a clock, it prints the name (Common Clock Framework) or
> + *   address (legacy clock framework) of the clock. ``[n]`` is optional.
> + * - ``Cr`` - For a clock, it prints the current rate of the clock.
> + * - ``G`` - For flags to be printed as a collection of symbolic strings that
> + *   would construct the specific value.
> + * - ``O`` - For a kobject based struct (device node).
> + * - ``x`` - For printing the address. Equivalent to ``%lx``.
> + */
> +
>  /*
>   * Show a '%p' thing.  A kernel extension is that the '%p' is followed
>   * by an extra set of alphanumeric characters that are extended format
>   * specifiers.
>   *
> + * Please see Documentation/printk-formats.rst for fuller description
> + * of specifier extensions. Also please update this file when making

"this file" is the file that I am reading?  or could it be "that file"?

> + * changes.
> + *
>   * Please update scripts/checkpatch.pl when adding/removing conversion
>   * characters.  (Search for "check for vsprintf extension").
>   *
> - * Right now we handle:
> - *
> - * - 'F' For symbolic function descriptor pointers with offset
> - * - 'f' For simple symbolic function names without offset
> - * - 'S' For symbolic direct pointers with offset
> - * - 's' For symbolic direct pointers without offset
> - * - '[FfSs]R' as above with __builtin_extract_return_addr() translation
> - * - 'B' For backtraced symbolic direct pointers with offset
> - * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
> - * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]
> - * - 'b[l]' For a bitmap, the number of bits is determined by the field
> - *       width which must be explicitly specified either as part of the
> - *       format string '%32b[l]' or through '%*b[l]', [l] selects
> - *       range-list format instead of hex format
> - * - 'M' For a 6-byte MAC address, it prints the address in the
> - *       usual colon-separated hex notation
> - * - 'm' For a 6-byte MAC address, it prints the hex address without colons
> - * - 'MF' For a 6-byte MAC FDDI address, it prints the address
> - *       with a dash-separated hex notation
> - * - '[mM]R' For a 6-byte MAC address, Reverse order (Bluetooth)
> - * - 'I' [46] for IPv4/IPv6 addresses printed in the usual way
> - *       IPv4 uses dot-separated decimal without leading 0's (1.2.3.4)
> - *       IPv6 uses colon separated network-order 16 bit hex with leading 0's
> - *       [S][pfs]
> - *       Generic IPv4/IPv6 address (struct sockaddr *) that falls back to
> - *       [4] or [6] and is able to print port [p], flowinfo [f], scope [s]
> - * - 'i' [46] for 'raw' IPv4/IPv6 addresses
> - *       IPv6 omits the colons (01020304...0f)
> - *       IPv4 uses dot-separated decimal with leading 0's (010.123.045.006)
> - *       [S][pfs]
> - *       Generic IPv4/IPv6 address (struct sockaddr *) that falls back to
> - *       [4] or [6] and is able to print port [p], flowinfo [f], scope [s]
> - * - '[Ii][4S][hnbl]' IPv4 addresses in host, network, big or little endian order
> - * - 'I[6S]c' for IPv6 addresses printed as specified by
> - *       http://tools.ietf.org/html/rfc5952
> - * - 'E[achnops]' For an escaped buffer, where rules are defined by combination
> - *                of the following flags (see string_escape_mem() for the
> - *                details):
> - *                  a - ESCAPE_ANY
> - *                  c - ESCAPE_SPECIAL
> - *                  h - ESCAPE_HEX
> - *                  n - ESCAPE_NULL
> - *                  o - ESCAPE_OCTAL
> - *                  p - ESCAPE_NP
> - *                  s - ESCAPE_SPACE
> - *                By default ESCAPE_ANY_NP is used.
> - * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form
> - *       "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
> - *       Options for %pU are:
> - *         b big endian lower case hex (default)
> - *         B big endian UPPER case hex
> - *         l little endian lower case hex
> - *         L little endian UPPER case hex
> - *           big endian output byte order is:
> - *             [0][1][2][3]-[4][5]-[6][7]-[8][9]-[10][11][12][13][14][15]
> - *           little endian output byte order is:
> - *             [3][2][1][0]-[5][4]-[7][6]-[8][9]-[10][11][12][13][14][15]
> - * - 'V' For a struct va_format which contains a format string * and va_list *,
> - *       call vsnprintf(->format, *->va_list).
> - *       Implements a "recursive vsnprintf".
> - *       Do not use this feature without some mechanism to verify the
> - *       correctness of the format string and va_list arguments.
> - * - 'K' For a kernel pointer that should be hidden from unprivileged users
> - * - 'NF' For a netdev_features_t
> - * - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
> - *            a certain separator (' ' by default):
> - *              C colon
> - *              D dash
> - *              N no separator
> - *            The maximum supported length is 64 bytes of the input. Consider
> - *            to use print_hex_dump() for the larger input.
> - * - 'a[pd]' For address types [p] phys_addr_t, [d] dma_addr_t and derivatives
> - *           (default assumed to be phys_addr_t, passed by reference)
> - * - 'd[234]' For a dentry name (optionally 2-4 last components)
> - * - 'D[234]' Same as 'd' but for a struct file
> - * - 'g' For block_device name (gendisk + partition number)
> - * - 'C' For a clock, it prints the name (Common Clock Framework) or address
> - *       (legacy clock framework) of the clock
> - * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address
> - *        (legacy clock framework) of the clock
> - * - 'Cr' For a clock, it prints the current rate of the clock
> - * - 'G' For flags to be printed as a collection of symbolic strings that would
> - *       construct the specific value. Supported flags given by option:
> - *       p page flags (see struct page) given as pointer to unsigned long
> - *       g gfp flags (GFP_* and __GFP_*) given as pointer to gfp_t
> - *       v vma flags (VM_*) given as pointer to unsigned long
> - * - 'O' For a kobject based struct. Must be one of the following:
> - *       - 'OF[fnpPcCF]'  For a device tree object
> - *                        Without any optional arguments prints the full_name
> - *                        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
> - *
> - * - 'x' For printing the address. Equivalent to "%lx".
> - *
> - * ** Please update also Documentation/printk-formats.txt when making changes **
> - *
>   * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
>   * function pointers are really function descriptors, which contain a
>   * pointer to the real address.
> 

ta.
-- 
~Randy

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