fstab-generator: if usr= is specified, mount it to /sysusr/usr/ first

This changes the fstab-generator to handle mounting of /usr/ a bit
differently than before. Instead of immediately mounting the fs to
/sysroot/usr/ we'll first mount it to /sysusr/usr/ and then add a
separate bind mount that mounts it from /sysusr/usr/ to /sysroot/usr/.

This way we can access /usr independently of the root fs, without for
waiting to be mounted via the /sysusr/ hierarchy. This is useful for
invoking systemd-repart while a root fs doesn't exist yet and for
creating it, with partition data read from the /usr/ hierarchy.

This introduces a new generic target initrd-usr-fs.target that may be
used to generically order services against /sysusr/ to become available.

5 files changed, 22 insertions, 4 deletions

diff --git a/units/initrd-usr-fs.target b/units/initrd-usr-fs.target
new file mode 100644
index 0000000000..7219655c9c
--- /dev/null
+++ b/units/initrd-usr-fs.target
@@ -0,0 +1,17 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Initrd /usr File System
+Documentation=man:systemd.special(7)
+AssertPathExists=/etc/initrd-release
+OnFailure=emergency.target
+OnFailureJobMode=replace-irreversibly
+DefaultDependencies=no
+Conflicts=shutdown.target
diff --git a/units/initrd.target b/units/initrd.target
index 655158a58b..fc8fbff4bd 100644
--- a/units/initrd.target
+++ b/units/initrd.target
@@ -14,6 +14,6 @@ OnFailure=emergency.target
 OnFailureJobMode=replace-irreversibly
 AssertPathExists=/etc/initrd-release
 Requires=basic.target
-Wants=initrd-root-fs.target initrd-root-device.target initrd-fs.target initrd-parse-etc.service
-After=initrd-root-fs.target initrd-root-device.target initrd-fs.target basic.target rescue.service rescue.target
+Wants=initrd-root-fs.target initrd-root-device.target initrd-fs.target initrd-usr-fs.target initrd-parse-etc.service
+After=initrd-root-fs.target initrd-root-device.target initrd-fs.target initrd-usr-fs.target basic.target rescue.service rescue.target
 AllowIsolate=yes
diff --git a/units/meson.build b/units/meson.build
index 15463760c6..fe8e95ff91 100644
--- a/units/meson.build
+++ b/units/meson.build
@@ -38,6 +38,7 @@ units = [
         ['initrd-switch-root.service',          'ENABLE_INITRD'],
         ['initrd-switch-root.target',           'ENABLE_INITRD'],
         ['initrd-udevadm-cleanup-db.service',   'ENABLE_INITRD'],
+        ['initrd-usr-fs.target',                'ENABLE_INITRD'],
         ['initrd.target',                       'ENABLE_INITRD'],
         ['kexec.target',                        ''],
         ['ldconfig.service',                    'ENABLE_LDCONFIG',
diff --git a/units/systemd-repart.service.in b/units/systemd-repart.service.in
index a5565834eb..60dc7783b3 100644
--- a/units/systemd-repart.service.in
+++ b/units/systemd-repart.service.in
@@ -12,7 +12,7 @@ Description=Repartition Root Disk
 Documentation=man:systemd-repart.service(8)
 DefaultDependencies=no
 Conflicts=shutdown.target
-After=sysroot.mount
+After=initrd-usr-fs.target
 Before=initrd-root-fs.target shutdown.target
 ConditionVirtualization=!container
 ConditionDirectoryNotEmpty=|/usr/lib/repart.d
diff --git a/units/systemd-volatile-root.service.in b/units/systemd-volatile-root.service.in
index 5ecc702b6d..468d85f968 100644
--- a/units/systemd-volatile-root.service.in
+++ b/units/systemd-volatile-root.service.in
@@ -12,7 +12,7 @@ Description=Enforce Volatile Root File Systems
 Documentation=man:systemd-volatile-root.service(8)
 DefaultDependencies=no
 Conflicts=shutdown.target
-After=sysroot.mount systemd-repart.service
+After=sysroot.mount sysroot-usr.mount systemd-repart.service
 Before=initrd-root-fs.target shutdown.target
 AssertPathExists=/etc/initrd-release