linux-kernel - Re: [PATCHv7 01/33] ns: Introduce Time Namespace

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Message-ID: <alpine.DEB.2.21.1910161230070.2046@nanos.tec.linutronix.de>
Date:   Wed, 16 Oct 2019 12:39:11 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
cc:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...nvz.org>,
        Adrian Reber <adrian@...as.de>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        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>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCHv7 01/33] ns: Introduce Time Namespace

On Wed, 16 Oct 2019, Vincenzo Frascino wrote:

< Trim 250+ lines ( 3+ pages) of pointlessly wasted electrons >

> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1096,6 +1096,13 @@ config UTS_NS
> >  	  In this namespace tasks see different info provided with the
> >  	  uname() system call
> >  
> > +config TIME_NS
> > +	bool "TIME namespace"
> > +	default y
> 
> Having CONFIG_TIME_NS "default y" makes so that the option is selected even on
> the architectures that have no support for time namespaces.
> The direct consequence is that the fallbacks defined in this patch are never
> selected and this ends up in kernel compilation errors due to missing symbols.
> 
> The error below shows what happens on arm64 (similar behavior on other
> architectures):
> 
> aarch64-linux-gnu-ld: kernel/time/namespace.o: in function `timens_on_fork':
> kernel/time/namespace.c:321: undefined reference to `vdso_join_timens'
> 
> My proposal is to keep TIME_NS "default n" (just remove "default y"), let the
> architectures that enable time namespaces select it and make CONFIG_TIME_NS
> select GENERIC_VDSO_TIME_NS if arch has HAVE_GENERIC_VDSO.

Nah.

config TIME_NS
	bool "TIME namespace"
	depends on GENERIC_VDSO_TIME_NS
	default y

and in lib/vdso/Kconfig

config GENERIC_VDSO_TIME_NS
	bool

and let architectures which have support for the VDSO bits select it.

< Trim another gazillion of useless lines >

See: https://people.kernel.org/tglx/notes-about-netiquette

Thanks,

	tglx