python ioctl

Thu Apr 14 09:25:02 EDT 2011

Nitish Sharma wrote:
> Hi PyPpl,
> For my current project I have a kernel device driver and a user-space
> application. This user-space application is already provided to me, and
> written in python. I have to extend this application with some addition
> features, which involves communicating with kernel device driver through
> ioctl() interface.
> I am fairly new with Python and not able to grok how to provide "op" in
> ioctl syntax - fcntl.ioctl (fd, op[, arg[, mutate_flag]]). Operations
> supported by device driver, through ioctl, are of the form: IOCTL_SET_MSG
> _IOR(MAGIC_NUMBER, 0, char*).
> It'd be great if some help can be provided about how to "encode" these
> operations in python to implement the desired functionality.
>> Regards
> Nitish
Here's some of my stuff. Specific to my device, but maybe you get some ideas
-------- eioctl.py ----
from ctypes import *
libc = CDLL ('/lib/libc.so.6')
#print libc.ioctl
def set_ioctl_argtype (arg_type):
 libc.ioctl.argtypes = (c_int, c_int, arg_type)
IOC_WRITE = 0x1
_IOC_NRBITS=	8
_IOC_TYPEBITS=	8
_IOC_SIZEBITS=	14
_IOC_DIRBITS=	2
_IOC_NRSHIFT=	0
_IOC_TYPESHIFT=	(_IOC_NRSHIFT+_IOC_NRBITS)
_IOC_SIZESHIFT=	(_IOC_TYPESHIFT+_IOC_TYPEBITS)
_IOC_DIRSHIFT=	(_IOC_SIZESHIFT+_IOC_SIZEBITS)
def IOC (dir, type, nr, size):
 return (((dir) << _IOC_DIRSHIFT) | \
	 ((type) << _IOC_TYPESHIFT) | \
	 ((nr) << _IOC_NRSHIFT) | \
	 ((size) << _IOC_SIZESHIFT))
def ioctl (fd, request, args):
 return libc.ioctl (fd, request, args)
--------------
example of usage:
 # Enable byte swap in driver
 from eioctl import IOC, IOC_WRITE
 EOS_IOC_MAGIC = 0xF4
 request = IOC(IOC_WRITE, EOS_IOC_MAGIC, 1, struct.calcsize ('i'))
 err = fcntl.ioctl(eos_fd, request, 1)