Merge ~enr0n/ubuntu/+source/systemd:ubuntu-kinetic into ~ubuntu-core-dev/ubuntu/+source/systemd:ubuntu-kinetic

[Nick Rosbrook]

Pull Debian fix for bug in systemd-resolved installation where dpkg refuses to install the symlink in chroot/container environments where /etc/resolv.conf is bind mounted.

[Lukas Märdian (slyon)]

armhf PASS: https://autopkgtest.ubuntu.com/results/autopkgtest-kinetic-enr0n-systemd-251/kinetic/armhf/s/systemd/20220830_190610_24590@/log.gz

[Lukas Märdian (slyon)]

The proposed changes LGTM in general!

Unfortunately, the autopkgtests somehow got lost on autopkgtest.u.c (all but armhf, which PASSed).
Working around those infrastructure issues, @enr0n was able to provide a local autopkgtest run (on amd64):

```
autopkgtest systemd --setup-commands 'apt install software-properties-common -y; apt-add-repository -y -s ppa:enr0n/systemd-251' --shell-fail -U -- qemu --ram-size=8192 --cpus=4 /home/nr/ubuntu/autopkgtest-testbeds/autopkgtest-kinetic-amd64.img
[...]
autopkgtest [10:43:41]: @@@@@@@@@@@@@@@@@@@@ summary
timedated PASS
hostnamed PASS
localed-locale PASS
localed-x11-keymap PASS
logind PASS
unit-config PASS
storage PASS
networkd-test.py PASS
build-login PASS
boot-and-services PASS
udev PASS
unit-tests PASS
tests-in-lxd PASS
upstream-1 PASS
upstream-2 PASS
boot-smoke PASS
systemd-fsckd SKIP exit status 77 and marked as skippable
qemu-system-x86_64: terminating on signal 15 from pid 46477 (/usr/bin/python3)
```

The test environment for the other architecutres (but armhf) is pretty similar to amd64, so I feel comfortable sponsoring this upload. If testing fails in -proposed, we might need to upgrade other architectures to `big_packages` (similar to amd64 & ppc64el)

review: Approve

diff --git a/debian/changelog b/debian/changelog
index c8ce2d4..a7df987 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,10 +1,51 @@
-systemd (251.4-1ubuntu2) UNRELEASED; urgency=medium
+systemd (251.4-1ubuntu2) kinetic; urgency=medium
 
+  [ Lukas Märdian ]
   * Provide upgrade path (Replaces:) for Jammy's systemd-repart (LP: 1897932)
     File: debian/control
     https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=2281670aa8007179170d5cc485bb94e3bbc3b63c
 
- -- Lukas Märdian <[e-mail]>  Tue, 30 Aug 2022 10:05:19 +0200
+  [ Luca Boccassi ]
+  * resolved: switch from .links to postinst/rm (LP: #1988300)
+    dpkg refuses to install the symlink in chroot/container environments
+    where /etc/resolv.conf is bind mounted:
+    | Unpacking systemd-resolved (251.4-1) ...
+    | dpkg: error processing archive /var/cache/apt/archives/systemd-resolved_251.4-1_amd64.deb (--unpack):
+    |  unable to make backup link of './etc/resolv.conf' before installing new version: Invalid cross-device link
+    So unfortunately manual handling via maintainerscripts is necessary.
+    Use maintainer scripts to avoid failing the installation, and provide
+    feedback to the user if the symlink cannot be successfully installed.
+    Also on removal, either copy /run/systemd/resolve/resolv.conf or
+    create an empty /etc/resolv.conf.
+    Amend to use the correct Ubuntu version string (251.4-1ubuntu2).
+    Author: Luca Boccassi
+    Files:
+    - debian/systemd-resolved.links
+    - debian/systemd-resolved.postinst
+    - debian/systemd-resolved.postrm
+    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=faf479a6158aac977c2cdb32fd1eaecc0862a7ef
+  * resolv.conf: take backup as a fallback
+    piuparts doesn't like seeing an empty resolv.conf after removing
+    the package, so take a backup and use it in case resolved/resolv.conf
+    is not available
+    Author: Luca Boccassi
+    Files:
+    - debian/systemd-resolved.postinst
+    - debian/systemd-resolved.postrm
+    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=c2b15f43eb7779953a3dda7f461edbb1bf038701
+
+  [ Nick Rosbrook ]
+  * debian/systemd-resolved.{postinst,postrm}: do not use DPKG_ROOT.
+    We cherry-picked "resolved: switch from .links to postinst/rm" and
+    "resolv.conf: take backup as a fallback" from debian/251.4-3 to fix a
+    systemd-resolved installation issue, but we are not taking the DPKG_ROOT
+    changes at the moment due to feature freeze.
+    Files:
+    - debian/systemd-resolved.postinst
+    - debian/systemd-resolved.postrm
+    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=5664be09ce9813cb2dd2bd71c5d325036655c312
+
+ -- Nick Rosbrook <[e-mail]>  Wed, 31 Aug 2022 09:55:31 -0400
 
 systemd (251.4-1ubuntu1) kinetic; urgency=medium
 
diff --git a/debian/systemd-resolved.links b/debian/systemd-resolved.links
deleted file mode 100644
index 63b933a..0000000
--- a/debian/systemd-resolved.links
+++ /dev/null
@@ -1 +0,0 @@
-/run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
diff --git a/debian/systemd-resolved.postinst b/debian/systemd-resolved.postinst
index 17ab957..e6beb29 100644
--- a/debian/systemd-resolved.postinst
+++ b/debian/systemd-resolved.postinst
@@ -25,4 +25,14 @@ if [ "$1" = configure ] && [ -z "$2" ]; then
     _adopt_conffile /etc/systemd/resolved.conf systemd-resolved
 fi
 
+if [ "$1" = configure ] && dpkg --compare-versions "$2" lt 251.4-1ubuntu2; then
+    if [ "$(readlink "/etc/resolv.conf")" != "../run/systemd/resolve/stub-resolv.conf" ] && [ "$(readlink "/etc/resolv.conf")" != "/run/systemd/resolve/stub-resolv.conf" ]; then
+        echo "Converting /etc/resolv.conf to a symlink to /run/systemd/resolve/stub-resolv.conf..."
+        if [ -f "/etc/resolv.conf" ]; then
+            mv "/etc/resolv.conf" "/etc/.resolv.conf.systemd-resolved.bak" || echo "Cannot take a backup of /etc/resolv.conf."
+        fi
+        ln -sf ../run/systemd/resolve/stub-resolv.conf "/etc/resolv.conf" || echo "Cannot install symlink from /etc/resolv.conf to ../run/systemd/resolve/stub-resolv.conf"
+    fi
+fi
+
 #DEBHELPER#
diff --git a/debian/systemd-resolved.postrm b/debian/systemd-resolved.postrm
new file mode 100644
index 0000000..9d6904f
--- /dev/null
+++ b/debian/systemd-resolved.postrm
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+set -e
+
+if [ "$1" = remove ]; then
+    if [ "$(readlink "/etc/resolv.conf")" = "../run/systemd/resolve/stub-resolv.conf" ] || [ "$(readlink "/etc/resolv.conf")" = "/run/systemd/resolve/stub-resolv.conf" ]; then
+        echo "Removing /etc/resolv.conf symlink to /run/systemd/resolve/stub-resolv.conf..."
+        rm -f "/etc/resolv.conf" || echo "Cannot remove /etc/resolv.conf."
+        if [ -f "/run/systemd/resolve/resolv.conf" ]; then
+            echo "Copying /run/systemd/resolve/resolv.conf to /etc/resolv.conf..."
+            cp "/run/systemd/resolve/resolv.conf" "/etc/resolv.conf" || echo "Cannot copy /run/systemd/resolve/resolv.conf to /etc/resolv.conf."
+            # We prefer a current resolv.conf rather than an older backup, if available
+            rm -f "/etc/.resolv.conf.systemd-resolved.bak"
+        elif [ -f "/etc/.resolv.conf.systemd-resolved.bak" ]; then
+            echo "Restoring previous resolv.conf..."
+            mv "/etc/.resolv.conf.systemd-resolved.bak" "/etc/resolv.conf" || echo "Cannot restore /etc/resolv.conf backup."
+        else
+            echo "Creating an empty /etc/resolv.conf..."
+            touch "/etc/resolv.conf" || echo "Cannot create an empty /etc/resolv.conf."
+        fi
+    fi
+fi
+
+#DEBHELPER#