linux-kernel - Re: [PATCH 1/4] ns: prepare time namespace for clone3()

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Message-ID: <20200318115731.3vn7cjchunk2bqoe@wittgenstein>
Date:   Wed, 18 Mar 2020 12:57:31 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     Adrian Reber <areber@...hat.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,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/4] ns: prepare time namespace for clone3()

On Wed, Mar 18, 2020 at 02:28:14PM +0300, Cyrill Gorcunov wrote:
> On Wed, Mar 18, 2020 at 12:17:26PM +0100, Christian Brauner wrote:
> > On Wed, Mar 18, 2020 at 01:57:47PM +0300, Cyrill Gorcunov wrote:
> > > On Tue, Mar 17, 2020 at 09:30:41AM +0100, Adrian Reber wrote:
> > > ...
> > > > +/*
> > > > + * This structure is used to set the time namespace offset
> > > > + * via /proc as well as via clone3().
> > > > + */
> > > > +struct set_timens_offset {
> > > > +	int			clockid;
> > > > +	struct timespec64	val;
> > > > +};
> > > > +
> > > 
> > > I'm sorry, I didn't follow this series much so can't comment right now.
> > > Still this structure made me a bit wonder -- the @val seems to be 8 byte
> > > aligned and I guess we have a useless pad between these members. If so
> > > can we swap them? Or it is already part of api?
> > 
> > It's not part of the api yet. We're still arguing about how and what we
> > want to pass down.
> 
> I see, thanks for info! So I think we could swap the members.

Yeah, _if_ we go with a version of this struct we definitely need to
ensure proper padding/alignment!