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)
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