[oe-core][PATCHv2] systemd: fix unmerged-bin tainted message

[<rs@ti.com>]

From: Randolph Sapp <rs@ti.com>

Systemd prefers both /bin and /sbin to link to /usr/bin. If this is not
the case it reports that the system is tainted in systemctl status.

Add a link from /usr/sbin to /usr/bin to prevent anything from being
excluded from the merged bin directory. This mimics the current merged
bin directory structure of Arch Linux [1].

Update the systemd recipe to prevent creating a duplicate link when
sbinmerge is enabled.

Override most sbin variables to point to their bin equivalent when
usermerge is enabled, with the exception being base_sbindir_native and
sbindir_native. There is no guarantee the host machine is using this
filesystem scheme.

This check was added to systemd back in 2024 [2].

[1] https://gitlab.archlinux.org/archlinux/packaging/packages/filesystem/-/blob/main/PKGBUILD
[2] https://github.com/systemd/systemd/commit/844863c61e7b501097da84a1e4d1e4a6aa6d9f0d

Signed-off-by: Randolph Sapp <rs@ti.com>
---

v2:
	- Use recommended replacement variable when usermerge is enabled
	- Apply replacement to other relevant variables in this file
	- Keep usrmerge distro feature separate as I believe there is still some
	  merit to mimicking a systemd filesystem in a non-systemd enabled
	  environment, and I didn't hear too much discussion previously

 meta/classes-recipe/populate_sdk_base.bbclass | 5 +++--
 meta/conf/bitbake.conf                        | 8 ++++----
 meta/recipes-core/systemd/systemd_259.5.bb    | 8 ++++++--
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/meta/classes-recipe/populate_sdk_base.bbclass b/meta/classes-recipe/populate_sdk_base.bbclass
index b427ff2761..15f393a3bb 100644
--- a/meta/classes-recipe/populate_sdk_base.bbclass
+++ b/meta/classes-recipe/populate_sdk_base.bbclass
@@ -186,9 +186,10 @@ POPULATE_SDK_POST_HOST_COMMAND:append:task-populate-sdk = " write_host_sdk_manif
 # Prepare the root links to point to the /usr counterparts.
 create_merged_usr_symlinks() {
     root="$1"
-    install -d $root${base_bindir} $root${base_sbindir} $root${base_libdir}
+    install -d $root${base_bindir} $root${base_libdir}
     ln -rs $root${base_bindir} $root/bin
-    ln -rs $root${base_sbindir} $root/sbin
+    ln -rs $root${base_bindir} $root/sbin
+    ln -rs $root${base_bindir} $root/usr/sbin
     ln -rs $root${base_libdir} $root/${baselib}
 
     if [ "${nonarch_base_libdir}" != "${base_libdir}" ]; then
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index 84450386d9..5d27e70b04 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -22,7 +22,7 @@ root_prefix = "${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', '${exec_prefi
 
 # Base paths
 export base_bindir = "${root_prefix}/bin"
-export base_sbindir = "${root_prefix}/sbin"
+export base_sbindir = "${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', '${base_bindir}', '${root_prefix}/sbin', d)}"
 export base_libdir = "${root_prefix}/${baselib}"
 export nonarch_base_libdir = "${root_prefix}/lib"
 
@@ -43,7 +43,7 @@ export systemd_user_unitdir = "${nonarch_libdir}/systemd/user"
 
 # Architecture dependent paths
 export bindir = "${exec_prefix}/bin"
-export sbindir = "${exec_prefix}/sbin"
+export sbindir = "${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', '${bindir}', '${exec_prefix}/sbin', d)}"
 export libdir = "${exec_prefix}/${baselib}"
 export libexecdir = "${exec_prefix}/libexec"
 export includedir = "${exec_prefix}/include"
@@ -65,9 +65,9 @@ bindir_cross = "/bin"
 bindir_crossscripts = "${bindir}/crossscripts"
 prefix_nativesdk = "/usr"
 bindir_nativesdk = "${prefix_nativesdk}/bin"
-sbindir_nativesdk = "${prefix_nativesdk}/sbin"
+sbindir_nativesdk = "${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', '${bindir_nativesdk}', '${prefix_nativesdk}/sbin', d)}"
 base_bindir_nativesdk = "/bin"
-base_sbindir_nativesdk = "/sbin"
+base_sbindir_nativesdk = "${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', '${base_bindir_nativesdk}', '/sbin', d)}"
 includedir_nativesdk = "${prefix_nativesdk}/include"
 libdir_nativesdk = "${prefix_nativesdk}/lib"
 base_libdir_nativesdk = "/lib"
diff --git a/meta/recipes-core/systemd/systemd_259.5.bb b/meta/recipes-core/systemd/systemd_259.5.bb
index c3cb605b4d..d84e38d7cd 100644
--- a/meta/recipes-core/systemd/systemd_259.5.bb
+++ b/meta/recipes-core/systemd/systemd_259.5.bb
@@ -69,6 +69,7 @@ PACKAGECONFIG ??= " \
     quotacheck \
     randomseed \
     resolved \
+    sbinmerge \
     serial-getty-generator \
     set-time-epoch \
     sysusers \
@@ -339,8 +340,11 @@ do_install() {
 		install -m 0644 ${UNPACKDIR}/org.freedesktop.hostname1_no_polkit.conf ${D}${datadir}/dbus-1/system.d/
 	fi
 
-	# create link for existing udev rules
-	ln -s ${base_bindir}/udevadm ${D}${base_sbindir}/udevadm
+	# create link for existing udev rules if sbinmerge is not enabled
+	if ${@bb.utils.contains('PACKAGECONFIG', 'sbinmerge', 'false', 'true', d)}
+	then
+		ln -s ${base_bindir}/udevadm ${D}${base_sbindir}/udevadm
+	fi
 
 	# install default policy for presets
 	# https://www.freedesktop.org/wiki/Software/systemd/Preset/#howto
-- 
2.53.0