core: do not attempt to add 'private' symlinks when RootImage/RootDirectory are used

A bind mount is added directly from private on the host to the actual
destination directory, no need for the symlinks (which cannot be created
as the bind mount happens first and creates the target as an actual directory)

Fixes https://github.com/systemd/systemd/issues/22264

test/units/testsuite-29.sh

@@ -6,10 +6,13 @@ set -eux
 set -o pipefail
 
 ARGS=()
+state_directory=/var/lib/private/
 if [[ -v ASAN_OPTIONS || -v UBSAN_OPTIONS ]]; then
     # If we're running under sanitizers, we need to use a less restrictive
     # profile, otherwise LSan syscall would get blocked by seccomp
     ARGS+=(--profile=trusted)
+    # With the trusted profile DynamicUser is disabled, so the storage is not in private/
+    state_directory=/var/lib/
 fi
 
 systemd-dissect --no-pager /usr/share/minimal_0.raw | grep -q '✓ portable service'
@@ -109,6 +112,12 @@ status="$(portablectl is-attached --extension app1 minimal_1)"
 
 portablectl detach --now --runtime --extension /usr/share/app1.raw /usr/share/minimal_1.raw app1
 
+# Ensure that the combination of read-only images, state directory and dynamic user works, and that
+# state is retained. Check after detaching, as on slow systems (eg: sanitizers) it might take a while
+# after the service is attached before the file appears.
+grep -q -F bar "${state_directory}/app0/foo"
+grep -q -F baz "${state_directory}/app1/foo"
+
 # portablectl also works with directory paths rather than images
 
 mkdir /tmp/rootdir /tmp/app0 /tmp/app1 /tmp/overlay /tmp/os-release-fix /tmp/os-release-fix/etc

test/units/testsuite-50.sh

@@ -308,7 +308,8 @@ systemd-run -P --property ExtensionImages="/usr/share/app0.raw /usr/share/app1.r
 cat >/run/systemd/system/testservice-50e.service <<EOF
 [Service]
 MountAPIVFS=yes
-TemporaryFileSystem=/run
+TemporaryFileSystem=/run /var/lib
+StateDirectory=app0
 RootImage=${image}.raw
 ExtensionImages=/usr/share/app0.raw /usr/share/app1.raw:nosuid
 # Relevant only for sanitizer runs
@@ -336,7 +337,8 @@ systemd-run -P --property ExtensionDirectories="${image_dir}/app0 ${image_dir}/a
 cat >/run/systemd/system/testservice-50f.service <<EOF
 [Service]
 MountAPIVFS=yes
-TemporaryFileSystem=/run
+TemporaryFileSystem=/run /var/lib
+StateDirectory=app0
 RootImage=${image}.raw
 ExtensionDirectories=${image_dir}/app0 ${image_dir}/app1
 # Relevant only for sanitizer runs