Re: [PATCH] locks: export device name

Davidlohr Bueso
2012-02-16T22:37:20Z

On Wed, 2012-02-15 at 12:39 -0800, Andrew Morton wrote:
> On Wed, 15 Feb 2012 07:42:30 -0500
> "J. Bruce Fields" <bfields@fieldses.org> wrote:
>
> > > > Perhaps safest would be to replace /proc/locks by another interface and
> > > > deprecate this one.
> > >
> > > If exporting the name in the current /proc/locks file is out of the
> > > question, then IMHO I don't think it would be worth adding a new
> > > interface just for such a small change.
> >
> > OK.
> >
> > If you want to just change this over, I guess the thing to do would be
> > to stick something in feature-removal-schedule.txt saying "we'll switch
> > this in 2 years" (or however long you think before there are
> > realistically no more lslk users left), then do it then.
> >
> > Switching to a new api would be better as we could warn users of the old
> > api then. Maybe it'd be worth it if there was some other change we'd
> > been wanting to make? Can't think of anything off the top of my head.
> >
> > We may be adding more lock types--will lslk and lslocks handle that
> > gracefully?
>
> Adding a whole new interface is pretty attractive. It lets us get it
> right this time. In particular, something which is extensible given
> certain simple rules. As we've learned, the current /proc/locks didn't
> get that right!

Ok, however I'm a bit confused on what you mean by extensible; since
what we decide to export to userspace is pretty much permanent, how can
we change (extend) it later? We'd pretty much be running into
the /proc/locks situation now.

>
> We can eventually remove the old code - it may take longer than two
> years, but whatever. If we go this way, we should arrange for the
> kernel to emit a warning (printk_once) into the logs the first time
> someone accesses the old file. This will help to prompt people to
> migrate off the deprecated interface. After a while, we can add a
> config option to make the old interface go away. Distros will start to
> disable the feature. Later, we zap it altogether.

Kind if like what was done with the /proc/x/oom_adj interface.