linux-kernel - Re: [PATCH v3 1/1] pidfd: implement PIDFD_THREAD flag for pidfd

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Date: Mon, 5 Feb 2024 16:22:41 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
	Tycho Andersen <tycho@...ho.pizza>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] pidfd: implement PIDFD_THREAD flag for
 pidfd_open()

On 02/02, Christian Brauner wrote:
>
> > @@ -2050,6 +2051,8 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
> >
> >  	seq_put_decimal_ll(m, "Pid:\t", nr);
> >
> > +	/* TODO: report PIDFD_THREAD */
>
> So I think we don't need to do anything here. Since PIDFD_THREAD sets
> O_EXCL in file->f_flags and in contrast to do_dentry_open() it isn't
> dropped. So userspace can already detect PIDFD_NONBLOCK as O_NONBLOCK
> and PIDFD_THREAD as O_EXCL.

Ah, indeed, I didn't know that fs/proc/fd.c:seq_show() reports ->f_flags.
Thanks.

OK, what about another TODO in sys_pidfd_send_signal() ?

I mean, should I send a simple patch which changes pidfd_send_signal()
to use do_send_specific() if PIDFD_THREAD ? Or do you think this should
be controlled by pidfd_send_signal's "flags" argument?

I honestly do not know what makes more sense.

Oleg.