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Date:   Mon, 17 Feb 2020 20:37:55 -0600
From: (Eric W. Biederman)
To:     Thomas Gleixner <>
Cc:     Christian Brauner <>,
        "Michael Kerrisk \(man-pages\)" <>,
        Dmitry Safonov <>,
        Andrei Vagin <>,
        Linux Kernel <>,
        Dmitry Safonov <>,
        Adrian Reber <>,
        Andy Lutomirski <>,
        Arnd Bergmann <>,
        Cyrill Gorcunov <>,
        "H. Peter Anvin" <>, Ingo Molnar <>,
        Jann Horn <>, Jeff Dike <>,
        Oleg Nesterov <>,
        Pavel Emelyanov <>,
        Shuah Khan <>,
        Vincenzo Frascino <>,
        containers <>,, Linux API <>,, Andrei Vagin <>
Subject: Re: Time Namespaces: CLONE_NEWTIME and clone3()?

Thomas Gleixner <> writes:

> Christian Brauner <> 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.

Short version.  If you are going to do migration of a container with
CRIU you want the time namespace in your container.  Possibly you can
avoid creating the time namespace until restore, but I don't think so.

Without the time namespace you get all kinds of applications that use
monotonic timers that will see their timers be ill behaved (probably
going backwards) over a checkpoint-restart event.


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