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Date:   Wed, 20 Mar 2019 22:00:11 +0100
From:   Christian Brauner <christian@brauner.io>
To:     Daniel Colascione <dancol@google.com>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: pidfd design
Message-ID: <20190320210009.hhgtcu4wkvsxg4sa@brauner.io>
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On Wed, Mar 20, 2019 at 01:50:43PM -0700, Daniel Colascione wrote:
> On Wed, Mar 20, 2019 at 1:47 PM Christian Brauner <christian@brauner.io> wrote:
> >
> > On Wed, Mar 20, 2019 at 11:39:10PM +0300, Alexey Dobriyan wrote:
> > > On Wed, Mar 20, 2019 at 01:14:01PM -0700, Daniel Colascione wrote:
> > > > On Wed, Mar 20, 2019 at 1:07 PM Alexey Dobriyan <adobriyan@gmail.com> wrote:
> > > > > > What would be your opinion to having a
> > > > > > /proc/<pid>/handle
> > > > > > file instead of having a dirfd.
> > > > >
> > > > > This is even worse than depending on PROC_FS. Just for the dependency
> > > > > pidfd code should be backed out immediately. Forget about /proc.
> > > >
> > > > We already have pidfds, and we've had them since /proc was added ages
> > > > ago.
> > >
> > > New pidfd code (or whatever the name) should NOT depend on /proc and
> > > should not interact with VFS at all at any point (other than probably
> > > being a descriptor on a fake filesystem). The reason is that /proc is
> > > full of crap and you don't want to spill that into new and hopefully
> > > properly designed part of new code.
> >
> > Yes, I agree. That's why I was thinking that translate_pid() is a good
> > candidate to provide that decoupling.
> 
> Then again: how do you propose fetching process metadata? If you adopt
> a stance that nothing can use procfs and simultaneously adopt a stance
> that we don't want to duplicate all the decades of metadata interfaces
> in /proc/pid (which are useful, not "crap"), then the overall result
> is that we just won't make any progress at all. There's nothing wrong
> with taking a dependency on procfs: procfs is how we talk about
> processes. It's completely unreasonable to say "no, you can't use the
> old thing" and also "no, we can't add a new thing that would duplicate
> the old thing".

This style or arguing won't get us any further. Please, send in the code
that you think is right and you want to get reviewed. If you can get the
Acks from the people you need, good.