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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 1 Apr 2019 09:15:00 -0700
Message-ID: <CAHk-=wi1UEsMv5wmBZB5S+5YiCbxd-AtVsoz1TfuD-KrdcLQew@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
To:     Jonathan Kowalski <bl0pbl33p@gmail.com>
Cc:     Daniel Colascione <dancol@google.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Kees Cook <keescook@chromium.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Joel Fernandes <joel@joelfernandes.org>
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On Mon, Apr 1, 2019 at 9:07 AM Jonathan Kowalski <bl0pbl33p@gmail.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