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SubjectRe: [PATCHv7 01/33] ns: Introduce Time Namespace
On Wed, Oct 16, 2019 at 12:39:11PM +0200, Thomas Gleixner wrote:
> 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

I was thinking to fix this by the same way with a small difference.

If GENERIC_GETTIMEOFDAY isn't set, it should be safe to allow enabling
TIME_NS. In this case, clock_gettime works via system call and we don't
have arch-specific code in this case. Does this sound reasonable?

depends on (!GENERIC_GETTIMEOFDAY || GENERIC_VDSO_TIME_NS)

Thanks,
Andrei

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