From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f66.google.com ([209.85.208.66]:42624 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726889AbfEPO6X (ORCPT ); Thu, 16 May 2019 10:58:23 -0400 Received: by mail-ed1-f66.google.com with SMTP id l25so5675863eda.9 for ; Thu, 16 May 2019 07:58:22 -0700 (PDT) Date: Thu, 16 May 2019 16:58:19 +0200 From: Christian Brauner Subject: Re: [PATCH v1 1/2] pid: add pidfd_open() Message-ID: <20190516145819.ofqkv6ozfpumhhuk@brauner.io> References: <20190516135944.7205-1-christian@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Geert Uytterhoeven Cc: David Howells , Jann Horn , Oleg Nesterov , Al Viro , "torvalds@linux-foundation.org" , Linux Kernel Mailing List , Arnd Bergmann , "linux-ia64@vger.kernel.org" , Linux-sh list , linux-mips@vger.kernel.org, Joel Fernandes , "open list:KERNEL SELFTEST FRAMEWORK" , sparclinux , elena.reshetova@intel.com, Linux-Arch , linux-s390 , Daniel Colascione , "Serge E. Hallyn" , linux-xtensa@linux-xtensa.org, Kees Cook , linux-m68k , Andy Lutomirski , Thomas Gleixner , Linux ARM , Parisc List , Linux API , cyphar@cyphar.com, Andy Lutomirski , "Eric W. Biederman" , alpha , Andrew Morton , linuxppc-dev Message-ID: <20190516145819.mrSxZPuOoep_PEbgFLqgpzZOFlzbKPD_TPGxLdbuhUU@z> On Thu, May 16, 2019 at 04:56:08PM +0200, Geert Uytterhoeven wrote: > 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 > rc1. Yep, already spotted this thanks to Arnd! Will change the syscall numbers. Thanks! Christian > > Note that none of this is part of linux-next. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > 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