Rik van Riel wrote:
>
> On Tue, 6 Feb 2001, Mike Silbersack wrote:
> > On Tue, 6 Feb 2001, Rik van Riel wrote:
> >
> > > The system call used to guarantee this is fsync (and friends?);
> > > if qmail doesn't use it but makes assumptions that aren't true
> > > on any decent OS out there ...
> >
> > Well, the various qmail programs do seem to fsync (though I'm
> > not sure if it's in the right places.)
>
> > ftp://elektroni.ee.tut.fi/pub/qmail_linux_metadata_message :
>
> > So what is this all about? qmail relies on the BSD semantics of
> ^^^
> > immediate update of directories on the disk when link(),
> > unlink(), open() and rename() calls are used.
>
> Pre-softupdate BSD semantics, apparently. Doesn't sound like
> the smartest thing to do when you want a reliable MTA...
This description is not entirely right.
Qmail depends on ordered-metadata updates (Terry! :-). That means
if you issue a link() to the new place and a unlink() in the old
place it should guarantee that the link() happens *BEFORE* the
unlink(). At least standard FFS/UFS does this. Linux ext2 might
do the the unlink() before the link() and a crash in that moment
will loose the file completely. It is all about the ordering
guarantee.
> > But Linux writes them to the disk asynchronously. My library
> > loaded before libc changes those calls to do the corresponding
> > directory writes too. Then qmail should be reliable against
> > power outages also in Linux.
>
> If djb could be considered to take things like reliability
> and the SMTP specification into account, and not just
> security, then qmail would have the potential to be a pretty
> decent mailer.
He did and qmail is one of the best and most reliable mailers on
the Internet.
> As it is, I can only recommend people to go with something
> like postfix, Exim or zmailer ...
Have a look at the qmail source and the facts before you spill
out such a *bullshit*!
--
Andre
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