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    SubjectRe: [PATCH] doc: convert printk-formats.txt to rst
    On Tue, Dec 5, 2017 at 5:45 PM, Tobin C. Harding <me@tobin.cc> 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.
    > - 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

    Awesome!

    >
    > Signed-off-by: Tobin C. Harding <me@tobin.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/index.rst b/Documentation/index.rst
    > index cb7f1ba5b3b1..83ace60efbe7 100644
    > --- a/Documentation/index.rst
    > +++ b/Documentation/index.rst
    > @@ -87,6 +87,16 @@ implementation.
    >
    > sh/index
    >
    > +Miscellaneous documentation
    > +---------------------------
    > +
    > +These guides contain general information useful when writing kernel code.
    > +
    > +.. toctree::
    > + :maxdepth: 1
    > +
    > + printk-formats

    I actually think this belongs in the kernel core API documentation
    list (Documentation/core-api/index.rst). I defer to Jon's opinion,
    though.

    > [...]
    > +.. kernel-doc:: lib/vsprintf.c
    > + :doc: Extended Format Pointer Specifiers

    Awesome!

    > [...]
    > +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.

    nit? You de-capitalized Kernel at the start but not at the end. "the
    Kernel handles ..."

    > [...]
    > 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
    > + * changes.

    Perhaps "... please update the kernel-doc above when making changes to
    this file." ?

    > + *
    > * 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.

    Is there no way to retain these per-flag details in the kernel-doc?
    Seems a shame to split up the docs if we can keep it together in here.

    > - * - '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.
    > --
    > 2.7.4
    >

    Nice work!

    -Kees

    --
    Kees Cook
    Pixel Security

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