systemctl: automatically softreboot/kexec if set up on reboot

Automatically softreboot if the nextroot has been set up with an OS
tree, or automatically kexec if a kernel has been loaded with kexec
--load.

Add SYSTEMCTL_SKIP_AUTO_KEXEC and SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT to
skip the automated switchover.

3 files changed, 30 insertions, 7 deletions

diff --git a/man/org.freedesktop.login1.xml b/man/org.freedesktop.login1.xml
index 4a94656f66..954518992b 100644
--- a/man/org.freedesktop.login1.xml
+++ b/man/org.freedesktop.login1.xml
@@ -595,16 +595,20 @@ node /org/freedesktop/login1 {
       <function>SuspendThenHibernateWithFlags()</function> add <varname>flags</varname> to allow for
       extendability, defined as follows:</para>
       <programlisting>
-#define SD_LOGIND_ROOT_CHECK_INHIBITORS  (UINT64_C(1) &lt;&lt; 0)
-#define SD_LOGIND_KEXEC_REBOOT           (UINT64_C(1) &lt;&lt; 1)
-#define SD_LOGIND_SOFT_REBOOT            (UINT64_C(1) &lt;&lt; 2)
+#define SD_LOGIND_ROOT_CHECK_INHIBITORS          (UINT64_C(1) &lt;&lt; 0)
+#define SD_LOGIND_KEXEC_REBOOT                   (UINT64_C(1) &lt;&lt; 1)
+#define SD_LOGIND_SOFT_REBOOT                    (UINT64_C(1) &lt;&lt; 2)
+#define SD_LOGIND_SOFT_REBOOT_IF_NEXTROOT_SET_UP (UINT64_C(1) &lt;&lt; 3)
       </programlisting>
       <para>When the <varname>flags</varname> is 0 then these methods behave just like the versions without
       flags. When <constant>SD_LOGIND_ROOT_CHECK_INHIBITORS</constant> (0x01) is set, active inhibitors are
-      honoured for privileged users too. When <constant>SD_LOGIND_KEXEC_REBOOT</constant> (0x02) is set, then
-      <function>RebootWithFlags()</function> performs a kexec reboot if kexec kernel is loaded. When
-      <constant>SD_LOGIND_SOFT_REBOOT</constant> (0x04) is set, then <function>RebootWithFlags()</function>
-      performs a userspace reboot only.</para>
+      honoured for privileged users too. When <constant>SD_LOGIND_KEXEC_REBOOT</constant> (0x02) is set,
+      then <function>RebootWithFlags()</function> performs a kexec reboot if kexec kernel is loaded. When
+      <constant>SD_LOGIND_SOFT_REBOOT</constant> (0x04) is set, or
+      <constant>SD_LOGIND_SOFT_REBOOT_IF_NEXTROOT_SET_UP</constant> (0x08) is set and a new root file system
+      has been set up on <literal>/run/nextroot/</literal>, then <function>RebootWithFlags()</function>
+      performs a userspace reboot only. <constant>SD_LOGIND_SOFT_REBOOT_IF_NEXTROOT_SET_UP</constant> and
+      <constant>SD_LOGIND_KEXEC_REBOOT</constant> can be combined, with soft-reboot having precedence.</para>
 
       <para><function>SetRebootParameter()</function> sets a parameter for a subsequent reboot operation.
       See the description of <command>reboot</command> in
diff --git a/man/systemctl.xml b/man/systemctl.xml
index 419d4a8243..217010ca1c 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -1652,6 +1652,13 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
             <para>This command honors <option>--force</option> and <option>--when=</option> in a similar way
             as <command>halt</command>.</para>
 
+            <para>If a new kernel has been loaded via <command>kexec --load</command>, a
+            <command>kexec</command> will be performed instead of a reboot, unless
+            <literal>SYSTEMCTL_SKIP_AUTO_KEXEC=1</literal> has been set. If a new root file system has
+            been setup on <literal>/run/nextroot</literal>, a <command>soft-reboot</command> will be
+            performed instead of a reboot, unless <literal>SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT=1</literal> has
+            been set.</para>
+
             <xi:include href="version-info.xml" xpointer="v246"/>
           </listitem>
         </varlistentry>
@@ -1681,6 +1688,10 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
 
             <para>This command honors <option>--force</option> and <option>--when=</option> similarly
             to <command>halt</command>.</para>
+
+            <para>If a new kernel has been loaded via <command>kexec --load</command>, a
+            <command>kexec</command> will be performed when <command>reboot</command> is invoked, unless
+            <literal>SYSTEMCTL_SKIP_AUTO_KEXEC=1</literal> has been set.</para>
           </listitem>
         </varlistentry>
 
@@ -1700,6 +1711,10 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
             <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
             for details.</para>
 
+            <para>If a new root file system has been setup on <literal>/run/nextroot</literal>, a
+            <command>soft-reboot</command> will be performed when <command>reboot</command> is invoked,
+            unless <literal>SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT=1</literal> has been set.</para>
+
             <xi:include href="version-info.xml" xpointer="v254"/>
           </listitem>
         </varlistentry>
diff --git a/man/systemd-soft-reboot.service.xml b/man/systemd-soft-reboot.service.xml
index 1de2fbc5f3..2419b86604 100644
--- a/man/systemd-soft-reboot.service.xml
+++ b/man/systemd-soft-reboot.service.xml
@@ -164,6 +164,10 @@ ExecStart=sleep infinity
     <para>Note that <filename>systemd-soft-reboot.service</filename> (and related units) should never be
     executed directly. Instead, trigger system shutdown with a command such as <literal>systemctl
     soft-reboot</literal>.</para>
+
+    <para>Note that if a new root file system has been setup on <literal>/run/nextroot</literal>, a
+    <command>soft-reboot</command> will be performed when the <command>reboot</command> command is
+    invoked.</para>
   </refsect1>
 
   <refsect1>