linux-kernel - Re: Time Namespaces: CLONE

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Message-ID: <874kvossh4.fsf@nanos.tec.linutronix.de>
Date:   Tue, 18 Feb 2020 00:29:27 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christian Brauner <christian.brauner@...ntu.com>,
        "Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>
Cc:     Dmitry Safonov <dima@...sta.com>, Andrei Vagin <avagin@...nvz.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Adrian Reber <adrian@...as.de>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        containers <containers@...ts.linux-foundation.org>,
        criu@...nvz.org, Linux API <linux-api@...r.kernel.org>,
        x86@...nel.org, Andrei Vagin <avagin@...il.com>
Subject: Re: Time Namespaces: CLONE_NEWTIME and clone3()?

Christian Brauner <christian.brauner@...ntu.com> writes:
> On Mon, Feb 17, 2020 at 10:47:53PM +0100, Michael Kerrisk (man-pages) wrote:
>> Actually, I think the alternative you propose just here is better. I
>> imagine there are times when one will want to create multiple
>> namespaces with a single call to clone3(), including a time namespace.
>> I think this should be allowed by the API. And, otherwise, clone3()
>> becomes something of a second-class citizen for creating namespaces.
>> (I don't really get the "less invasive" argument. Implementing this is
>> just a piece of kernel to code to make user-space's life a bit simpler
>> and more consistent.)
>
> I don't particularly mind either way. If there's actual users that need
> to set it at clone3() time then we can extend it. So I'd like to hear
> what Adrian, Dmitry, and Thomas think since they are well-versed how
> this will be used in the wild. I'm weary of exposing a whole new uapi
> struct and extending clone3() without any real use-case but I'm happy to
> if there is!

I really have no clue. I merily helped getting this in shape without
creating havoc for timekeeping and VDSO. I have to punt to the container
wizards.

Thanks,

        tglx