[bug#34859] [PATCH] pack: "-RR" produces PRoot-enabled relocatable binaries.

["Ludovic Courtès" <ludovic.courtes@inria.fr>]

Hi there!

Ludovic Courtès <ludo@gnu.org> skribis:

>  @item --relocatable
>  @itemx -R
>  Produce @dfn{relocatable binaries}---i.e., binaries that can be placed
> -anywhere in the file system hierarchy and run from there.  For example,
> -if you create a pack containing Bash with:
> +anywhere in the file system hierarchy and run from there.
> +
> +When this option is passed once, the resulting binaries require support for
> +@dfn{user namespaces} in the kernel Linux; when passed
> +@emph{twice}@footnote{Here's a trick to memorize it: @code{-RR}, which adds
> +PRoot support, can be thought of as the abbreviation of ``Really
> +Relocatable''.  Neat, isn't it?}, relocatable binaries fall to back to PRoot
> +if user namespaces are unavailable, and essentially work anywhere---see below
> +for the implications.

For the record, we had discussed this idea a while back¹, and I was
recently reminded of it when looking at udocker².

Udocker has a third method to achieve file system virtualization, which
is to use Debian’s Fakechroot³.  Fakechroot is an LD_PRELOAD-based
thing, so it’s more lightweight than PRoot but also more fragile.  I
don’t think it’d be interesting for us to support that method in
addition to user namespaces and PRoot.

Thoughts?

Ludo’.

¹ https://lists.gnu.org/archive/html/guix-devel/2018-04/msg00252.html
² https://github.com/indigo-dc/udocker/
³ https://github.com/dex4er/fakechroot/wiki