[Samba] Need a cross-platform lockfile algorithm

[Phil Endecott]

Dear Experts,

I'm hoping that your experience with SMB and CIFS means that you're 
familiar with cross-platform file locking.  I need a 
lowest-common-denominator whole-file locking method that will work on 
as many combinations of client and server systems as possible; in 
particular it needs to run on

- Linux client talking to NFS server.
- Linux client talking to Samba server.
- Linux client talking to Windows server.
- Windows client talking to Samba server.
- Windows client talking to Windows server.
- Linux local disk access.
- Windows local disk access.
No doubt each of those combinations has many variations.

I only need advisory locking, not mandatory locking; a lockfile 
convention would be fine.  I'm hoping that something like the algorithm 
used by liblockfile could be used (see man lockfile_create, e.g. 
http://pwet.fr/man/linux/fonctions_bibliotheques/lockfile_create).  
Basically it creates a file with a unique name, links it to the 
<filename>.lock file, and uses stat() to see if its link got there 
before any other contender.  This is designed to be NFS-safe but I 
don't know if it would be possible or safe in an SMB or CIFS environment.

I'm sure this must have been solved before but I can't find anything 
especially helpful; maybe I'm not searching for the right keywords.

If anyone can point me in the right direction I would be very grateful.


Regards,

Phil.