[ovs-dev] [PATCH] daemon: Avoid the link() syscall.

[Ben Pfaff]

On Fri, Nov 16, 2012 at 02:52:48PM -0800, Ethan Jackson wrote:
> > I don't see why we're scheduling tmpfile to get deleted on exit.  We're
> > about to rename it away to pidfile.  After we do that, someone else may
> > come along and newly create a file with that name and lock it on the way
> > to trying to acquire the pidfile.  Deleting it will screw up that
> > procedure.
> 
> The reason is that if we die in between taking the lock, and doing the
> actual rename, we leave a stale tmpfile sitting around.  It's not really a
> problem in the scheme of things, it just looks a bit messy.  I think we can
> solve the problem you site by simply calling
> fatal_signal_remove_file_to_unlink() immediately after doing the rename.

Hmm, I guess that's OK given that we don't process fatal signals
immediately but only after we get back to the main loop.

> > rename is always atomic, so I'm not sure what the statement about
> >  atomicity adds here.
> 
> I meant that the whole operation is atomic, as opposed to opening the
> pidfile, locking it, and then writing to it, during which
> you'd briefly have an empty/half-written pidfile.  That said, I agree this
> comment is unclear and not particularly useful.  I'll remove it.

OK, thanks.