Archive Mail, Exim and Locking Bug? (was RE: [MAILSCANNER] Locki ng failing?)

[Tony Finch]

"Desai, Jason" <jase at SENSIS.COM> wrote:
>
>I am testing out my new MailScanner server and I think I see a problem with
>message locking when I have Archive Mail set.  To test, I send an email with
>a large attachment which will take several seconds to scan.  When I have
>
>Archive Mail = /var/spool/MailScanner/archive
>
>it seems that all 3 of my MailScanner processes scan the same single email
>and 2 of them (as would be expected) have problems moving the email to the
>out queue (see logs below).  But if I comment out Archive Mail and send the
>same email again, only one MailScanner process scans the email and moves it
>to the out queue with no problem.
>
>I also tried setting Lock Type = flock (just as a test) and sent the same
>email again.  With this, only one MailScanner process scanned the mail and
>moved it to the out queue fine.  But I don't think I should keep it this way
>because I am using Exim.  Is this a bug?  Is anyone else using Exim and
>Archive Mail?  Can anyone else duplicate this?

I think I've worked out where the problem comes from, and I caused it :-(
The FreeBSD fcntl manual page says:

     This interface follows the completely stupid semantics of System V and
     IEEE Std 1003.1-1988 (``POSIX.1'') that require that all locks associated
     with a file for a given process are removed when any file descriptor for
     that file is closed by that process.

which has implications for MailScanner when it copies messages around :-(

I'll be back at some point with a patch.

Tony.
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