linux-kernel - Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add CLONE

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Message-ID: <87zho8bl8x.fsf@oldenburg2.str.redhat.com>
Date:   Mon, 29 Apr 2019 22:38:06 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jann Horn <jannh@...gle.com>, Kevin Easton <kevin@...rana.org>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Aleksa Sarai <cyphar@...har.com>,
        "Enrico Weigelt\, metux IT consult" <lkml@...ux.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add CLONE_PIDFD]

* Linus Torvalds:

> On Mon, Apr 29, 2019 at 12:55 PM Jann Horn <jannh@...gle.com> wrote:
>>
>> ... I guess that already has a name, and it's called vfork(). (Well,
>> except that the Linux vfork() isn't a real vfork().)
>
> What?
>
> Linux vfork() is very much a real vfork(). What do you mean?

In Linux-as-the-ABI (as opposed to Linux-as-the-implementation), vfork
is sometimes implemented as fork, so applications cannot rely on the
vfork behavior regarding the stopped parent and the shared address
space.

In fact, it would be nice to have a flag we can check in the posix_spawn
implementation, so that we can support vfork-as-fork without any run
time cost to native Linux.

Thanks,
Florian