linux-kernel - Re: clone3: allow creation of time namespace with offset

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Message-ID: <CAK8P3a18YySozk6P77JpS58Hbtz=QQmLKw+PrzXbdOwtOQQuJA@mail.gmail.com>
Date:   Thu, 19 Mar 2020 09:16:43 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Adrian Reber <areber@...hat.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Aleksa Sarai <cyphar@...har.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: clone3: allow creation of time namespace with offset

On Thu, Mar 19, 2020 at 9:11 AM Adrian Reber <areber@...hat.com> wrote:

> With Arnd's idea of only using nanoseconds, timens_offset would then
> contain something like this:
>
> struct timens_offset {
>         __aligned_s64 monotonic_offset_ns;
>         __aligned_s64 boottime_offset_ns;
> };
>
> I kind of prefer adding boottime and monotonic directly to struct clone_args
>
>         __aligned_u64 tls;
>         __aligned_u64 set_tid;
>         __aligned_u64 set_tid_size;
> +       __aligned_s64 monotonic_offset_ns;
> +       __aligned_s64 boottime_offset_ns;
>  };

I would also prefer the second approach using two 64-bit integers
instead of a pointer, as it keeps the interface simpler to implement
and simpler to interpret by other tools.

      Arnd