[PATCH v2] Dockerfile.isar: Pull qemu-user-static from buster-backports

[Jan Kiszka <jan.kiszka@siemens.com>]

From: Jan Kiszka <jan.kiszka@siemens.com>

This is needed for running fakeroot from bullseye and sid which triggers
an unimplemented syscall with the current version.

Due to changes in the new qemu-user-static package, the current approach
to activate its binfmt settings no longer works. Instead, switch to an
explicit call of the binfmt-support in init script.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Changes in v2:
 - fix binfmt activation
 - drop unneeded (and effectless) listing of binfmt-support for
   buster-backports

OK, this was a nice one:
 - debootstrap (of buster) creates the rootfs initially with a link of
   $target/proc -> /proc
 - later, it tries to umount $target/proc (and then sets up a proper 
   mounting via chroot) - I consider this a bug of debootstrap
 - for us, umount $target/proc, which is effectively umount /proc,
   because /proc/sys/fs/binfmt_misc is mounted
 - debootstrap ignores this error
 - but due to the issue in v1, binfmt_misc wasn't mounted, and the
   problem started...

 Dockerfile.isar | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Dockerfile.isar b/Dockerfile.isar
index 6b325f3..cde63b0 100644
--- a/Dockerfile.isar
+++ b/Dockerfile.isar
@@ -3,7 +3,9 @@
 FROM kasproject/kas:latest
 
 ENV LC_ALL=en_US.UTF-8
-RUN apt-get update && \
+RUN echo 'deb http://deb.debian.org/debian buster-backports main' > /etc/apt/sources.list.d/buster-backports.list && \
+    echo "Package: qemu-user-static\nPin: release n=buster-backports\nPin-Priority: 501\n\nPackage: *\nPin: release n=buster-backports\nPin-Priority: -1" > /etc/apt/preferences.d/qemu-user-static && \
+    apt-get update && \
     apt-get install -y -f --no-install-recommends \
             autoconf automake gdisk libtool bash-completion \
             sudo grub2 grub-efi-amd64-bin grub-efi-ia32-bin \
@@ -18,4 +20,4 @@ RUN echo "builder ALL=NOPASSWD: ALL" > /etc/sudoers.d/builder-nopasswd && \
 RUN echo "Defaults env_keep += \"ftp_proxy http_proxy https_proxy no_proxy\"" \
     > /etc/sudoers.d/env_keep && chmod 660 /etc/sudoers.d/env_keep
 
-RUN sed -i 's|#!/bin/bash|\0\n\ndpkg-reconfigure qemu-user-static 2>\&1 \| grep -v "already enabled in kernel"|' /kas/docker-entrypoint
+RUN sed -i 's|#!/bin/bash|\0\n\n/etc/init.d/binfmt-support start|' /kas/docker-entrypoint
-- 
2.26.2