Re: [PATCH 1/4] pidfd: support PIDFD_NONBLOCK in pidfd_open()

[Christian Brauner]

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