Invalid argument with fcntl.fcntl

I am trying to use the advisory locking with fcntl over NFS (thus, me
choosing fcntl instead of flock and friends).

I have the following code:
lockdata = struct.pack ("hhllhh", fcntl.F_RDLCK, 0, 0, 0, 0, 0)
print self.fd, type (self.fd), len (lockdata), type (lockdata)
ret = fcntl.fcntl (self.fd, fcntl.F_GETLK, lockdata)

when this code executes, I always get the following:

<open file '', mode 'a' at 0xb7e99458> <type 'file'> 16 <type
'str'> Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "", line 154, in _get_lock_state_nfs
ret = fcntl.fcntl (self.fd, fcntl.F_GETLK, lockdata)
IOError: [Errno 22] Invalid argument

If I execute the same code in the Python interpreter (replacing self.fd
with an open file object), it work.

Can anyone shed some light on why this code would produce that error?

Mitko Haralanov mitko@xxxxxxxxxx
Senior Software Engineer 650.934.8064
System Interconnect Group

FORTRAN is a good example of a language which is easier to parse
using ad hoc techniques.
-- D. Gries
[What's good about it? Ed.]