On Tue, May 21, 2019 at 04:32:20PM +0200, Christian Brauner wrote: > On Mon, May 20, 2019 at 05:56:29PM +0200, 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 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 > > pidfds 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. > > > > Signed-off-by: Christian Brauner <christian@xxxxxxxxxx> > > Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx> > > This now also carries a Reviewed-by from David. > > > Acked-by: Arnd Bergmann <arnd@xxxxxxxx> > > Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Cc: Jann Horn <jannh@xxxxxxxxxx> > > Cc: David Howells <dhowells@xxxxxxxxxx> > > Cc: Andy Lutomirsky <luto@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Aleksa Sarai <cyphar@xxxxxxxxxx> > > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > Cc: linux-api@xxxxxxxxxxxxxxx > > I've moved pidfd_open() into my for-next branch together with Joel's > pidfd polling changes. Everything is based on v5.2-rc1. > > The chosen syscall number for now is 434. David is going to send out > another pile of mount api related syscalls. I'll coordinate with him > accordingly prior to the 5.3 merge window. After talking to Arnd, I split the syscall addition and the per-arch wiring-up of pidfd_open() into two patches. There are no functional changes and everything is still sitting in for-next. Thanks! Christian
