Mailbox locking

[Niko Tyni <ntyni@iki.fi>]

Hi,

while trying to avoid fixing the Mail::Audit bugs, I've run
into the same mbox locking problem with Email::LocalDelivery.
Oh well.

Upstream is still using simply flock(LOCK_EX). Debian policy says
"use fcntl() first and dot locking after this".

Using fcntl() locks from Perl seems a bit tricky, since I'll have to
pack() the lock argument together myself. I need some advice here.
The corresponding struct in /usr/include/bits/fcntl.h is

struct flock
  {
    short int l_type;   /* Type of lock: F_RDLCK, F_WRLCK, or F_UNLCK.  */
    short int l_whence; /* Where `l_start' is relative to (like `lseek').  */
#ifndef __USE_FILE_OFFSET64
    __off_t l_start;    /* Offset where the lock begins.  */
    __off_t l_len;      /* Size of the locked area; zero means until EOF.  */
#else
    __off64_t l_start;  /* Offset where the lock begins.  */
    __off64_t l_len;    /* Size of the locked area; zero means until EOF.  */
#endif
    __pid_t l_pid;      /* Process holding the lock.  */
  };


I'm a bit worried about the __off64_t stuff. Can I assume that these are
of the 'l' type for pack()? What about pid_t? The best hit on Google I found,
<http://pleac.sourceforge.net/include/perl/ch07/lockarea>, has
my $FLOCK_STRUCT = 's s l l i';

The dotlocking part is easy to do by execing dotlockfile(1) from liblockfile1;
it can't be done inside the module because it needs setgid mail privileges.

Cheers,
-- 
Niko