mmdebstrap/hooks/merged-usr/setup00.sh

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#!/bin/sh
#
# mmdebstrap does have a --merged-usr option but only as a no-op for
# debootstrap compatibility
#
# Using this hook script, you can emulate what debootstrap does to set up
# merged /usr via directory symlinks, even using the exact same shell function
# that debootstrap uses by running mmdebstrap with:
#
# --setup-hook=/usr/share/mmdebstrap/hooks/merged-usr/setup00.sh
#
# Alternatively, you can setup merged-/usr by installing the usrmerge package:
#
# --include=usrmerge
#
# mmdebstrap will not include this functionality via a --merged-usr option
# because there are many reasons against implementing merged-/usr that way:
#
# https://wiki.debian.org/Teams/Dpkg/MergedUsr
# https://wiki.debian.org/Teams/Dpkg/FAQ#Q:_Does_dpkg_support_merged-.2Fusr-via-aliased-dirs.3F
# https://lists.debian.org/20190219044924.GB21901@gaara.hadrons.org
# https://lists.debian.org/YAkLOMIocggdprSQ@thunder.hadrons.org
# https://lists.debian.org/20181223030614.GA8788@gaara.hadrons.org
#
# In addition, the merged-/usr-via-aliased-dirs approach violates an important
# principle of component based software engineering one of the core design
# ideas/goals of mmdebstrap: All the information to create a chroot of a Debian
# based distribution should be included in its packages and their metadata.
# Using directory symlinks as used by debootstrap contradicts this principle.
# The information whether a distribution uses this approach to merged-/usr or
# not is not anymore contained in its packages but in a tool from the outside.
#
# Example real world problem: I'm using debbisect to bisect Debian unstable
# between 2015 and today. For which snapshot.d.o timestamp should a merged-/usr
# chroot be created and for which ones not?
#
# The problem is not the idea of merged-/usr but the problem is the way how it
# got implemented in debootstrap via directory symlinks. That way of rolling
# out merged-/usr is bad from the dpkg point-of-view and completely opposite of
# the vision with which in mind I wrote mmdebstrap.
set -eu
if [ "$MMDEBSTRAP_VERBOSITY" -ge 3 ]; then
set -x
fi
TARGET="$1"
ARCH=$(dpkg --print-architecture)
eval "$(APT_CONFIG="$MMDEBSTRAP_APT_CONFIG" apt-config shell ARCH Apt::Architecture)"
if [ -e /usr/share/debootstrap/functions ]; then
. /usr/share/debootstrap/functions
doing_variant () { [ $1 != "buildd" ]; }
MERGED_USR="yes"
setup_merged_usr
else
link_dir=""
case $ARCH in
hurd-*) exit 0;;
amd64) link_dir="lib32 lib64 libx32" ;;
i386) link_dir="lib64 libx32" ;;
mips|mipsel) link_dir="lib32 lib64" ;;
mips64*|mipsn32*) link_dir="lib32 lib64 libo32" ;;
powerpc) link_dir="lib64" ;;
ppc64) link_dir="lib32 lib64" ;;
ppc64el) link_dir="lib64" ;;
s390x) link_dir="lib32" ;;
sparc) link_dir="lib64" ;;
sparc64) link_dir="lib32 lib64" ;;
x32) link_dir="lib32 lib64 libx32" ;;
esac
link_dir="bin sbin lib $link_dir"
for dir in $link_dir; do
ln -s usr/"$dir" "$TARGET/$dir"
mkdir -p "$TARGET/usr/$dir"
done
fi