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Re: [Nmh-workers] Locking (specifically, sequences)

From: Lyndon Nerenberg
Subject: Re: [Nmh-workers] Locking (specifically, sequences)
Date: Fri, 8 Mar 2013 07:40:46 -0800

On 2013-03-08, at 2:12 AM, Tethys wrote:

> : flock()  does not lock files over NFS.  Use fcntl(2) instead: that does
> : work over NFS, given a sufficiently  recent  version  of  Linux  and  a
> : server which supports locking.

NFS is a bit of a no-mans land in this regard.  The is no consistency between 
OSes as to what works over NFS[234].  Or CIFS, AFS, 9fs, or any number of other 
networked filesystems.

POSIX says fcntl() is it, so we must support that.  But I'm not sure we can 
guarantee that we don't do anything that will cause us to unintentionally lose 
locks.  Making this sort of proof is tricky, and requires a lot of discipline 
to maintain moving forward.  Having flock() as an alternative decreases the 
potential for accidental lock lossage.  I very much want the option of using it 
when it's available.  (And on the systems I use, flock() does work over NFS 


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