attribute documentation

abi2doc is a helper tool for generating and formatting sysfs attribute documentation which is location under Documentation/ABI in the kernel source code.

From a rough estimate, there are around 2000 attributes that are undocumented in the kernel.

The ABI documentation format looks like the following:

abi2doc can fill in the 'Date' and the 'KernelVersion' fields with high accuracy. The 'Contact' details is prompted for once, and the others 'What' and 'Description' are prompted on every attribute.

It also tries to collect description from various sources-

• From the commit message that introduced the attribute
• From comments around the attribute show/store functions or the attribute

declaring macro.

• From the structure fields that map to the attribute.

  For eg. consider the attribute declaring macro PORT_RO(dest_id) and its show function port_destid_show(...).

static ssize_t
port_destid_show(struct device *dev, struct device_attribute *attr,
                 char *buf)
{
        struct rio_mport *mport = to_rio_mport(dev);

        if (mport)
                return sprintf(buf, "0x%04x\n", mport->host_deviceid);
        else
                return -ENODEV;
}

The show functions typically contain a conversion to a driver private struct and then one or many fields from it are put in the buffer.

In the example above, the driver private structure is a struct of type rio_mport and the attribute port_id maps to the field host_deviceid in the structure.

struct rio_mport {
      ...
      int host_deviceid;      /* Host device ID */
      struct rio_ops *ops;    /* low-level architecture-dependent routines */
      unsigned char id;       /* port ID, unique among all ports */
      ...
      };

There's a comment against host_deviceid here and this can be extracted.

All sysfs attribute declaring macros are located in abi2doc/macros.txt. Each row of macros.txt contains an attribute declaring macro space separated by the location of the attribute name in the macro - DEVICE_ATTR 0. This list is not complete. Please send a pull request if you find any that are not in the list.

Usage

Prerequisites:

• Coccinelle - install instructions

spatch will need to be compiled with option ./configure --with-python=python3

• Python 3
• Linux Kernel source code

abi2doc is available on PYPI. Install with pip3:

pip3 install abi2doc

The library is currently tested against Python versions 3.4+.

usage: abi2doc [-h] -f SOURCE_FILE -o OUTPUT_FILE

Helper for documenting Linux Kernel sysfs attributes

required arguments:
  -f SOURCE_FILE  linux source file to document
  -o OUTPUT_FILE  location of the generated sysfs ABI documentation

optional arguments:
  -h, --help      show this help message and exit

Example usage:

abi2doc -f drivers/video/backlight/lp855x_bl.c -o sysfs_doc.txt

The script will fill in the 'Date' and the 'KernelVersion' fields for found attributes. The 'Contact' details is prompted for once, and the others 'What' and 'Description' are prompted on every attribute. The entered description will be followed by hints, as shown in a generated file below.

What:       /sys/class/backlight/<backlight>/bled_mode
Date:       Oct, 2012
KernelVersion:  3.7
Contact:    dri-devel@lists.freedesktop.org
Description:
        (WO) Write to the backlight mapping mode. The backlight current
        can be mapped for either exponential (value "0") or linear
        mapping modes (default).
        --------------------------------
        %%%%% Hints below %%%%%
        bled_mode DEVICE_ATTR drivers/video/backlight/lm3639_bl.c 220
        --------------------------------
        %%%%% store fn comments %%%%%
        /* backlight mapping mode */
        --------------------------------
        %%%%% commit message %%%%%
        commit 0f59858d511960caefb42c4535dc73c2c5f3136c
        Author: G.Shark Jeong <gshark.jeong@gmail.com>
        Date:   Thu Oct 4 17:12:55 2012 -0700

            backlight: add new lm3639 backlight driver

            This driver is a general version for LM3639 backlgiht + flash driver chip
            of TI.

            LM3639:
            The LM3639 is a single chip LCD Display Backlight driver + white LED
            Camera driver.  Programming is done over an I2C compatible interface.
            www.ti.com

            [akpm@linux-foundation.org: code layout tweaks]
            Signed-off-by: G.Shark Jeong <gshark.jeong@gmail.com>
            Cc: Richard Purdie <rpurdie@rpsys.net>
            Cc: Daniel Jeong <daniel.jeong@ti.com>
            Cc: Randy Dunlap <rdunlap@xenotime.net>
            Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
            Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Expected time for the scripts to run =

(num of attrs x avg 4 min per attr)/num of cores.

Contributions

Contributions are welcome, whether it is in the form of code or documentation. Please refer to the issues tab for places that need help.