Re: [exim-dev] mbx locking bug in CYGWIN

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Auteur: Philip Hazel
Datum:  
Aan: Derek Martin
CC: exim-dev
Onderwerp: Re: [exim-dev] mbx locking bug in CYGWIN
On Thu, 17 Mar 2005, Derek Martin wrote:

> Understood. OTOH, if it is a legitimate bug, knowing about it,
> wouldn't you want to fix it?


Yes, I would. The problem here is in the knowing... :-)

> > I wonder why we have had no problems with user mailboxes on NFS (for a
> > system with three separate hosts) over the last 8 or so years, then?
>
> It could just be that you've been lucky...
>
> In all honesty, the race conditions involved are (as I understand it)
> such that should be exceedingly rare to encounter a problem.


Did I mention that we do you the lock files + link() trick? As well as
fcntl() locks. Looks like I forgot.

> It would mean that the MDA and the MUA would have to, at the exact
> same time, both request an exclusive lock on the same file, and the
> request which came over NFS came first but was interrupted before it
> completed. Even on busy mail spool files, how likely is that to
> happen?


I did say "mailboxes", not spool files. (Assuming the Exim usage of
the word "spool".) I wouldn't put a mail spool (in the Exim sense) on
NFS. But from your mention of MUAs, I guess you were meaning mailboxes.

-- 
Philip Hazel            University of Cambridge Computing Service,
ph10@???      Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book:    http://www.uit.co.uk/exim-book