Re: [PATCH] Fix switch_root/pivot_root cut-n-paste error in configure.ac

[Karel Zak <kzak@redhat.com>]

On Thu, Jul 24, 2014 at 12:52:26PM -0400, Dave Reisner wrote:
> On Wed, Jul 23, 2014 at 07:39:02PM +0200, Andreas Henriksson wrote:
> > The "linux only" check for pivot_root seems to suffer from
> > a cut-n-paste problem from the earlier switch_root part.
> > 
> > Signed-off-by: Andreas Henriksson <andreas@fatal.se>
> > ---
> >  configure.ac | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/configure.ac b/configure.ac
> > index db53dff..aae2456 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -1193,7 +1193,7 @@ AC_ARG_ENABLE([pivot_root],
> >    [], [UL_DEFAULT_ENABLE([pivot_root], [check])]
> >  )
> >  UL_BUILD_INIT([pivot_root])
> > -UL_REQUIRES_LINUX([switch_root])
> > +UL_REQUIRES_LINUX([pivot_root])
> 
> Is this really correct? Seems to me like the check should simply be
> removed. 

 It's definitely better to check that the system is Linux before you
 start to check for something more complicated. There is logical "and"
 between all UL_REQUIRES_*, so the first unsuccessful check disabled
 the rest.

> In sys-utils/pivot_root.c, we have the following:
> 
>   #define pivot_root(new_root,put_old) syscall(SYS_pivot_root,new_root,put_old)
> 
> So, the subsequent check for the syscall seems like the only necessary
> check needed. As is, I think that u-l now fails to build in places where
> the pivot_root wrapper doesn't exist in the libc, but the syscall exists
> (does such a platform even exist?).

 There is no glibc wrapper at all, in code we always call the syscall
 and in configure.ac we check for SYS_pivot_root sycall on Linux.
 Nowhere we care about libc.

    Karel


-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com