linux-kernel - Re: [PATCH 2/4] clone: add CLONE

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Date:   Mon, 15 Apr 2019 12:52:09 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
        jannh@...gle.com, dhowells@...hat.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, serge@...lyn.com, luto@...nel.org,
        arnd@...db.de, ebiederm@...ssion.com, keescook@...omium.org,
        tglx@...utronix.de, mtk.manpages@...il.com,
        akpm@...ux-foundation.org, cyphar@...har.com,
        joel@...lfernandes.org, dancol@...gle.com
Subject: Re: [PATCH 2/4] clone: add CLONE_PIDFD

On 04/14, Christian Brauner wrote:
>
> @@ -2260,6 +2363,10 @@ long _do_fork(unsigned long clone_flags,
>  	}
>
>  	put_pid(pid);
> +
> +	if (clone_flags & CLONE_PIDFD)
> +		nr = pidfd;
> +

Well, this doesn't look nice ...

CLONE_PARENT_SETTID doesn't look very usefule, so what if we add

	if ((clone_flags & (CLONE_PIDFD|CLONE_PARENT_SETTID)) ==
	                   (CLONE_PIDFD|CLONE_PARENT_SETTID))
		return ERR_PTR(-EINVAL);

at the start of copy_process() ?

Then it can do

	if (clone_flags & CLONE_PIDFD) {
		retval = pidfd_create(pid, &pidfdf);
		if (retval < 0)
			goto bad_fork_free_pid;
		retval = put_user(retval, parent_tidptr)
		if (retval < 0)
			goto bad_fork_free_pid;
	}

Oleg.