linux-kernel - Re: [PATCH v2 0/5] pid: add pidfd

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Date:   Sun, 31 Mar 2019 14:17:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christian Brauner <christian@...uner.io>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Daniel Colascione <dancol@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        Jonathan Kowalski <bl0pbl33p@...il.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()

On Sun, Mar 31, 2019 at 2:10 PM Christian Brauner <christian@...uner.io> wrote:
>
> I don't think that we want or can make them equivalent since that would
> mean we depend on procfs.

Sure we can.

If /proc is enabled, then you always do that dance YOU ALREADY WROTE
THE CODE FOR to do the stupid ioctl.

And if /procfs isn't enabled, then you don't do that.

Ta-daa. Done. No stupid ioctl, and now /proc and pidfd_open() return
the same damn thing.

And guess what? If /proc isn't enabled, then obviously pidfd_open()
gives you the /proc-less thing, but at least there is no crazy "two
different file descriptors for the same thing" situation, because then
the /proc one doesn't exist.

Notice? No incompatibility. No crazy stupid new "convert one to the
other", because "the other model" NEVER EXISTS. There is only one
pidfd - it might be proc-less if CONFIG_PROC isn't there, but let's
face it, nobody even cares, because nobody ever disabled /proc anyway.

And no need for some new "convert" interface (ioctl or other).

Problem solved.

                   Linus