linux-kernel - Re: [PATCH 1/4] pidfd: support PIDFD_NONBLOCK in pidfd

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Date:   Tue, 1 Sep 2020 18:33:08 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Sargun Dhillon <sargun@...gun.me>,
        Aleksa Sarai <cyphar@...har.com>,
        linux-kselftest@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Jens Axboe <axboe@...nel.dk>, linux-api@...r.kernel.org
Subject: Re: [PATCH 1/4] pidfd: support PIDFD_NONBLOCK in pidfd_open()

On Tue, Sep 01, 2020 at 06:23:10PM +0200, Oleg Nesterov wrote:
> On 08/31, Christian Brauner wrote:
> >
> > --- /dev/null
> > +++ b/include/uapi/linux/pidfd.h
> > @@ -0,0 +1,12 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +
> > +#ifndef _UAPI_LINUX_PIDFD_H
> > +#define _UAPI_LINUX_PIDFD_H
> > +
> > +#include <linux/types.h>
> > +#include <linux/fcntl.h>
> > +
> > +/* Flags for pidfd_open().  */
> > +#define PIDFD_NONBLOCK O_NONBLOCK
> > +
> > +#endif /* _UAPI_LINUX_PIDFD_H */
> 
> Why? Can't we simply use O_NONBLOCK ?

It's the same thing we seem to do for any other (anon inode) fds:

include/linux/eventfd.h:#define		EFD_NONBLOCK O_NONBLOCK
include/uapi/linux/inotify.h:#define	IN_NONBLOCK O_NONBLOCK
include/uapi/linux/signalfd.h:#define	SFD_NONBLOCK O_NONBLOCK
include/uapi/linux/timerfd.h:#define	TFD_NONBLOCK O_NONBLOCK

also for O_CLOEXEC:

include/linux/eventfd.h:#define		EFD_CLOEXEC O_CLOEXEC
include/linux/userfaultfd_k.h:#define	UFFD_CLOEXEC O_CLOEXEC
include/uapi/linux/eventpoll.h:#define	EPOLL_CLOEXEC O_CLOEXEC
include/uapi/linux/mount.h:#define	OPEN_TREE_CLOEXEC    O_CLOEXEC
include/uapi/linux/perf_event.h:#define PERF_FLAG_FD_CLOEXEC (1UL << 3) /* O_CLOEXEC */
include/uapi/linux/signalfd.h:#define	SFD_CLOEXEC O_CLOEXEC
include/uapi/linux/timerfd.h:#define	TFD_CLOEXEC O_CLOEXEC

So I think we should just do the same. A clean flag namespace seems
nicer to me too tbh.

Christian