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

[Andreas Henriksson <andreas@fatal.se>]

Hello Dave Reisner!

On Thu, Jul 24, 2014 at 12:52:26PM -0400, Dave Reisner wrote:
> Is this really correct? Seems to me like the check should simply be
> removed. 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?).

I cought this when trying to build on Debian GNU/kFreeBSD (with incorrect
configure flags for that platform) where the SYS_pivot_root check
failed the build.
Not knowing anything about non-linux architectures myself it was not obvious
to me why this was.

Passing --disable-pivot_root fixed the build and it would be more
obvious that this is the correct thing to do if it was pointed out that
this is only expected to work on Linux.
I consider the UL_REQUIRES_LINUX check as a more obvious
way to point out this error so people like myself doesn't need to
spend so much time scratching their heads over this.

>From what I can tell, Linux is the only system offering this syscall anyway.
Do you know of any non-linux system offering this?
If not, then I think the check is still correct and helpful.

Regards,
Andreas Henriksson