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

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Date:   Sun, 31 Mar 2019 14:03:25 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Christian Brauner <christian@...uner.io>,
        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 1:38 PM Andy Lutomirski <luto@...capital.net> wrote:
>
> openat(fd to pidfd’s proc directory, “status”, ...);
>
> And we want a non-utterly-crappy way to do this.  The ioctl is certainly ugly, but it *works*.

It's beyond clunky. It's a disgrace.

If people really want equivalency between open("/proc/%d") and some
new pidfd_open(), then just *make* the two equivalent.

No effing crappy ioctl idiocy to create one from the other. Just make
the damn things be the exact same thing (and then if we extend clone()
to return one, make that return the same exact thing too).

Btw, we have several clone bits left:

 - if we don't have CLONE_PARENT set, the low 8 bits are still available

 - ignoring that, wehave bit #12 free: It used to be CLONE_IDLETASK
long long ago, but it was always kernel-only so it's never been
exposed as a user space bit.

                  Linus