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

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Date:   Mon, 1 Apr 2019 09:15:00 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jonathan Kowalski <bl0pbl33p@...il.com>
Cc:     Daniel Colascione <dancol@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Andy Lutomirski <luto@...capital.net>,
        Christian Brauner <christian@...uner.io>,
        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>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()

On Mon, Apr 1, 2019 at 9:07 AM Jonathan Kowalski <bl0pbl33p@...il.com> wrote:
>
> With the POLLHUP model on a simple pidfd, you'd know when the process
> you were referring to is dead (and one can map POLLPRI to dead and
> POLLHUP to zombie, etc).

Adding ->poll() to the pidfd should be easy. Again, it would be
trivially be made to work for the directory fd you get from
/proc/<pid> too.

Yeah, yeah, pollable directories are odd, but the vfs layer doesn't
care about things like "is this a directory or not". It will just call
the f_op->poll() method.

              Linus