Question

I need to find who locked a file using python (posix/linux). Currently I use this method:

flk = struct.pack('hhqql', fcntl.F_WRLCK, 0, 0, 0, 0)
flk = struct.unpack('hhqql', fcntl.fcntl(self.__file, fcntl.F_GETLK , flk))

if flk[0] == fcntl.F_UNLCK:
    # file is unlocked ...
else:
    pid = flk[4]

This solution is not architecture-independent. Structure passed to fcntl contains fields such as off_t or pid_t. I cannot make assumptions about sizes of those types.

struct flock {
    ...
    short l_type;    /* Type of lock: F_RDLCK,
                    F_WRLCK, F_UNLCK */
    short l_whence;  /* How to interpret l_start:
                    SEEK_SET, SEEK_CUR, SEEK_END */
    off_t l_start;   /* Starting offset for lock */
    off_t l_len;     /* Number of bytes to lock */
    pid_t l_pid;     /* PID of process blocking our lock
                    (F_GETLK only) */
    ...
};

Is there any other way to find the PID? Or maybe sizes of off_t and pid_t? The solution must be fully portable between different architectures.

Edit
I decided to use lsof program as suggested below. Another option is to parse /proc/locks file.

Answer 1

Maybe you can try use external program, lsof, to do that?

   Lsof revision 4.85 lists on its standard output file information 
   about files opened by processes for the following UNIX dialects:

        AIX 5.3
        Apple Darwin 9 and Mac OS X 10.[56]
        FreeBSD 4.9 and 6.4 for x86-based systems
        FreeBSD 8.[02] and 9.0 for AMD64-based systems
        Linux 2.1.72 and above for x86-based systems
        Solaris 9, 10 and 11