Create initrd-root-device.target synchronization point (#3239)

Add a synchronization point so that custom initramfs units can run
after the root device becomes available, before it is fsck'd and
mounted.

This is useful for custom initramfs units that may modify the
root disk partition table, where the root device is not known in
advance (it's dynamically selected by the generators).

10 files changed, 71 insertions, 4 deletions

diff --git a/Makefile.am b/Makefile.am
index aea91e9c94..c126f65ad2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -467,6 +467,7 @@ dist_systemunit_DATA = \
 	units/local-fs-pre.target \
 	units/initrd.target \
 	units/initrd-fs.target \
+	units/initrd-root-device.target \
 	units/initrd-root-fs.target \
 	units/remote-fs.target \
 	units/remote-fs-pre.target \
diff --git a/man/bootup.xml b/man/bootup.xml
index b92057af29..986996398c 100644
--- a/man/bootup.xml
+++ b/man/bootup.xml
@@ -179,6 +179,8 @@
     identical to the system manager bootup (see above) until it
     reaches <filename>basic.target</filename>. From there, systemd
     approaches the special target <filename>initrd.target</filename>.
+    When the root device becomes available,
+    <filename>initd-root-device.target</filename> is reached.
     If the root device can be mounted at
     <filename>/sysroot</filename>, the
     <filename>sysroot.mount</filename> unit becomes active and
@@ -204,7 +206,10 @@
                                                |                                 emergency.service
                         ______________________/|                                         |
                        /                       |                                         v
-                       |                  sysroot.mount                          <emphasis>emergency.target</emphasis>
+                       |            initrd-root-device.target                    <emphasis>emergency.target</emphasis>
+                       |                       |
+                       |                       v
+                       |                  sysroot.mount
                        |                       |
                        |                       v
                        |             initrd-root-fs.target
diff --git a/man/systemd.special.xml b/man/systemd.special.xml
index 14998b9647..26974ed73f 100644
--- a/man/systemd.special.xml
+++ b/man/systemd.special.xml
@@ -83,6 +83,7 @@
     <filename>remote-fs.target</filename>,
     <filename>remote-fs-pre.target</filename>,
     <filename>rescue.target</filename>,
+    <filename>initrd-root-device.target</filename>,
     <filename>initrd-root-fs.target</filename>,
     <filename>rpcbind.target</filename>,
     <filename>runlevel2.target</filename>,
@@ -465,6 +466,18 @@
         </listitem>
       </varlistentry>
       <varlistentry>
+        <term><filename>initrd-root-device.target</filename></term>
+        <listitem>
+          <para>A special initrd target unit that is reached when the root filesystem device is available, but before
+          it has been mounted.
+          <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+          and
+          <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+          automatically setup the appropiate dependencies to make this happen.
+          </para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
         <term><filename>initrd-root-fs.target</filename></term>
         <listitem>
           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
diff --git a/src/basic/special.h b/src/basic/special.h
index 2fd03d9f75..084d3dfa23 100644
--- a/src/basic/special.h
+++ b/src/basic/special.h
@@ -52,6 +52,7 @@
 #define SPECIAL_LOCAL_FS_TARGET "local-fs.target"
 #define SPECIAL_LOCAL_FS_PRE_TARGET "local-fs-pre.target"
 #define SPECIAL_INITRD_FS_TARGET "initrd-fs.target"
+#define SPECIAL_INITRD_ROOT_DEVICE_TARGET "initrd-root-device.target"
 #define SPECIAL_INITRD_ROOT_FS_TARGET "initrd-root-fs.target"
 #define SPECIAL_REMOTE_FS_TARGET "remote-fs.target"       /* LSB's $remote_fs */
 #define SPECIAL_REMOTE_FS_PRE_TARGET "remote-fs-pre.target"
diff --git a/src/fstab-generator/fstab-generator.c b/src/fstab-generator/fstab-generator.c
index 343e3b1817..108522873e 100644
--- a/src/fstab-generator/fstab-generator.c
+++ b/src/fstab-generator/fstab-generator.c
@@ -489,6 +489,7 @@ static int parse_fstab(bool initrd) {
 static int add_sysroot_mount(void) {
         _cleanup_free_ char *what = NULL;
         const char *opts;
+        int r;
 
         if (isempty(arg_root_what)) {
                 log_debug("Could not find a root= entry on the kernel command line.");
@@ -508,6 +509,13 @@ static int add_sysroot_mount(void) {
                 opts = arg_root_options;
 
         log_debug("Found entry what=%s where=/sysroot type=%s", what, strna(arg_root_fstype));
+
+        if (is_device_path(what)) {
+                r = generator_write_initrd_root_device_deps(arg_dest, what);
+                if (r < 0)
+                        return r;
+        }
+
         return add_mount(what,
                          "/sysroot",
                          arg_root_fstype,
diff --git a/src/gpt-auto-generator/gpt-auto-generator.c b/src/gpt-auto-generator/gpt-auto-generator.c
index af96adec06..a4938a7c3a 100644
--- a/src/gpt-auto-generator/gpt-auto-generator.c
+++ b/src/gpt-auto-generator/gpt-auto-generator.c
@@ -956,6 +956,12 @@ static int add_root_mount(void) {
          * wait for a root device to show up. A udev rule will create
          * the link for us under the right name. */
 
+        if (in_initrd()) {
+                r = generator_write_initrd_root_device_deps(arg_dest, "/dev/gpt-auto-root");
+                if (r < 0)
+                        return 0;
+        }
+
         return add_mount(
                         "root",
                         "/dev/gpt-auto-root",
diff --git a/src/shared/generator.c b/src/shared/generator.c
index cd3c35cd55..70afc6a285 100644
--- a/src/shared/generator.c
+++ b/src/shared/generator.c
@@ -65,7 +65,7 @@ static int write_fsck_sysroot_service(const char *dir, const char *what) {
                 "Description=File System Check on %2$s\n"
                 "DefaultDependencies=no\n"
                 "BindsTo=%3$s\n"
-                "After=%3$s local-fs-pre.target\n"
+                "After=initrd-root-device.target local-fs-pre.target\n"
                 "Before=shutdown.target\n"
                 "\n"
                 "[Service]\n"
@@ -191,3 +191,17 @@ int generator_write_timeouts(
                                     "[Unit]\nJobTimeoutSec=%s",
                                     program_invocation_short_name, timeout);
 }
+
+int generator_write_initrd_root_device_deps(const char *dir, const char *what) {
+        _cleanup_free_ char *unit = NULL;
+        int r;
+
+        r = unit_name_from_path(what, ".device", &unit);
+        if (r < 0)
+                return log_error_errno(r, "Failed to make unit name from path: %m");
+
+        return write_drop_in_format(dir, SPECIAL_INITRD_ROOT_DEVICE_TARGET, 50, "root-device",
+                                    "# Automatically generated by %s\n\n"
+                                    "[Unit]\nRequires=%s\nAfter=%s",
+                                    program_invocation_short_name, unit, unit);
+}
diff --git a/src/shared/generator.h b/src/shared/generator.h
index a734e13970..a6017c1b76 100644
--- a/src/shared/generator.h
+++ b/src/shared/generator.h
@@ -34,3 +34,7 @@ int generator_write_timeouts(
         const char *where,
         const char *opts,
         char **filtered);
+
+int generator_write_initrd_root_device_deps(
+        const char *dir,
+        const char *what);
diff --git a/units/initrd-root-device.target b/units/initrd-root-device.target
new file mode 100644
index 0000000000..9d44d2d303
--- /dev/null
+++ b/units/initrd-root-device.target
@@ -0,0 +1,15 @@
+#  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 Root Device
+Documentation=man:systemd.special(7)
+ConditionPathExists=/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 eae7c703c1..8be7e2b399 100644
--- a/units/initrd.target
+++ b/units/initrd.target
@@ -12,6 +12,6 @@ OnFailure=emergency.target
 OnFailureJobMode=replace-irreversibly
 ConditionPathExists=/etc/initrd-release
 Requires=basic.target
-Wants=initrd-root-fs.target initrd-fs.target initrd-parse-etc.service
-After=initrd-root-fs.target initrd-fs.target basic.target rescue.service rescue.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
 AllowIsolate=yes