ioctl-opt

Pythonified linux asm-generic/ioctl.h .

So you can replicate driver's code computing fcntl.ioctl's opt argument.

For example, starting from the following IOCTL declaration (taken from input.h):

.. code:: C

#include <sys/ioctl.h> #define EVIOCGNAME(len) _IOC(_IOC_READ, 'E', 0x06, len) /* get device name */

you could write the following:

.. code:: python

from ioctl_opt import IOC, IOC_READ EVIOCGNAME = lambda length: IOC(IOC_READ, ord('E'), 0x06, length)

The differences are minimal, and all come from python language or coding style:

• macros/constants to use from ioctl_opt for not start with an underscore
• defined macro becomes a callable (here a lambda, could be function)
• IOC's nr argument has to be an integer, so C's single-quote char becomes an ord call
• avoid shadowing built-in len function

The length argument is an object (typically serving as an I/O buffer with the fcntl.ioctl() call), the size of which is incorporated in the generated ioctl opt value. IOC() will calculate the size of the object. Supported object types are:

• any ctypes type or instance
• memoryview
• bytearray
• struct.Struct
• array.array

You may want to then write a pythonic function to conveniently access that ioctl:

.. code:: python

import ctypes import fcntl

def getDeviceName(fd, length=1024): name = (ctypes.c_char * length)() actual_length = fcntl.ioctl(fd, EVIOCGNAME(length), name, True) if actual_length < 0: raise OSError(-actual_length) if name[actual_length - 1] == b'\x00': actual_length -= 1 return name[:actual_length]

More advanced example defining hidraw ioctls, requiring structures (for more on how structures are defined, check python's ctype documentation for your python version):

.. code:: python

import ctypes from ioctl_opt import IOR, IOC, IOC_READ, IOC_WRITE

hid.h

HID_MAX_DESCRIPTOR_SIZE = 4096

hidraw.h

class hidraw_report_descriptor(ctypes.Structure): fields = [ ('size', ctypes.c_uint), ('value', ctypes.c_ubyte * HID_MAX_DESCRIPTOR_SIZE), ]

class hidraw_devinfo(ctypes.Structure): fields = [ ('bustype', ctypes.c_uint), ('vendor', ctypes.c_short), ('product', ctypes.c_short), ]

HIDIOCGRDESCSIZE = IOR(ord('H'), 0x01, ctypes.c_int) HIDIOCGRDESC = IOR(ord('H'), 0x02, hidraw_report_descriptor) HIDIOCGRAWINFO = IOR(ord('H'), 0x03, hidraw_devinfo) HIDIOCGRAWNAME = lambda length: IOC(IOC_READ, ord('H'), 0x04, length) HIDIOCGRAWPHYS = lambda length: IOC(IOC_READ, ord('H'), 0x05, length) HIDIOCSFEATURE = lambda length: IOC(IOC_WRITE|IOC_READ, ord('H'), 0x06, length) HIDIOCGFEATURE = lambda length: IOC(IOC_WRITE|IOC_READ, ord('H'), 0x07, length)