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Date:   Thu, 16 May 2019 16:56:08 +0200
From:   Geert Uytterhoeven <>
To:     Christian Brauner <>,
        David Howells <>
Cc:     Jann Horn <>, Oleg Nesterov <>,
        Al Viro <>,
        "" <>,
        Linux Kernel Mailing List <>,
        Arnd Bergmann <>,
        "" <>,
        Linux-sh list <>,,
        Joel Fernandes <>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        sparclinux <>,, Linux-Arch <>,
        linux-s390 <>,
        Daniel Colascione <>,
        "Serge E. Hallyn" <>,, Kees Cook <>,
        linux-m68k <>,
        Andy Lutomirski <>,
        Thomas Gleixner <>,
        Linux ARM <>,
        Parisc List <>,
        Linux API <>,,
        Andy Lutomirski <>,
        "Eric W. Biederman" <>,
        alpha <>,
        Andrew Morton <>,
        linuxppc-dev <>
Subject: Re: [PATCH v1 1/2] pid: add pidfd_open()

Hi Christian, David,

On Thu, May 16, 2019 at 4:00 PM Christian Brauner <> wrote:
> This adds the pidfd_open() syscall. It allows a caller to retrieve pollable
> pidfds for a process which did not get created via CLONE_PIDFD, i.e. for a
> process that is created via traditional fork()/clone() calls that is only
> referenced by a PID:
> int pidfd = pidfd_open(1234, 0);
> ret = pidfd_send_signal(pidfd, SIGSTOP, NULL, 0);
> With the introduction of pidfds through CLONE_PIDFD it is possible to
> created pidfds at process creation time.
> However, a lot of processes get created with traditional PID-based calls
> such as fork() or clone() (without CLONE_PIDFD). For these processes a
> caller can currently not create a pollable pidfd. This is a huge problem
> for Android's low memory killer (LMK) and service managers such as systemd.
> Both are examples of tools that want to make use of pidfds to get reliable
> notification of process exit for non-parents (pidfd polling) and race-free
> signal sending (pidfd_send_signal()). They intend to switch to this API for
> process supervision/management as soon as possible. Having no way to get
> pollable pidfds from PID-only processes is one of the biggest blockers for
> them in adopting this api. With pidfd_open() making it possible to retrieve
> pidfd for PID-based processes we enable them to adopt this api.
> In line with Arnd's recent changes to consolidate syscall numbers across
> architectures, I have added the pidfd_open() syscall to all architectures
> at the same time.

> +428    common  pidfd_open                      sys_pidfd_open

This number conflicts with "[PATCH 4/4] uapi: Wire up the mount API
syscalls on non-x86 arches", which is requested to be included before

Note that none of this is part of linux-next.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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