I'm doing some USB user-space driver programming 
in Python 2.1.3 under Linux 2.4.

When using a particular ioctl (HIDIOCGNAME), the 
return value as well as the (copy_to_user) binary data 
is significant.

Here is the code from line 547 of hiddev.c (kernel 
2.4.19-pre7):
  if (_IOC_NR(cmd) == _IOC_NR(HIDIOCGNAME(0))) {
    int len;
    if (!hid->name) return 0;
    len = strlen(hid->name) + 1;
    if (len > _IOC_SIZE(cmd)) len = _IOC_SIZE(cmd);
    return copy_to_user((char *) arg, hid->name, len) ?
      -EFAULT : len;
  }

So here is the problem:  fcntl.ioctl() will only give me 
one or the other value, but not both.

I can work around this by initialising the input buffer to 
all chr(0), and then strip them off after.  But there will 
be a time when an ioctl call *requires* both values.

Until now I have appreciated the simple ioctl interface, 
but now it is shown to be an oversimplification.

It may be that POSIX, or some standard somewhere 
says that ioctl should not be used to do this, but 
maybe Python should support it anyway.

I suggest either:
1.  A new function ioctl2(fd, op, arg) that returns a 
2-tuple of (return_value, binary_buffer) and does not 
try to interpret the return value.
2.  An optional 4th parameter whose presence (but 
not value) requests the 2-tuple mentioned in (1).

Gotta love Python!