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

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Message-ID: <CAHk-=wiPv4QJBC0qX8xxnT5P2C7S5uDG0HKdvdSpcoXaHG91tQ@mail.gmail.com>
Date:   Mon, 29 Apr 2019 14:31:30 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Florian Weimer <fweimer@...hat.com>
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]

On Mon, Apr 29, 2019 at 1:38 PM Florian Weimer <fweimer@...hat.com> wrote:
>
> 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.

What broken library does that?

Sure, we didn't have a proper vfork() long long long ago. But that
predates both git and BK, so it's some time in the 90's. We've had a
proper vfork() *forever*.

> 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.

No. Just make a bug-report to whatever broken library you use. What's
the point of having a library that can't even get vfork() right? Why
would you want to have a flag to say "vfork is broken"?

                 Linus