shared: add new IMAGE_VERSION=/IMAGE_ID= field to /etc/os-release

This specifes two new optional fields for /etc/os-release:
IMAGE_VERSION= and IMAGE_ID= that are supposed to identify the image of
the current booted system by name and version.

This is inspired by the versioning stuff in
https://github.com/systemd/mkosi/pull/683.

In environments where pre-built images are installed and updated as a
whole the existing os-release version/distro identifier are not
sufficient to describe the system's version, as they describe only the
distro an image is built from, but not the image itself, even if that
image is deployed many times on many systems, and even if that image
contains more resources than just the RPMs/DEBs.

In particular, "mkosi" is a tool for building disk images based on
distro RPMs with additional resources dropped in. The combination of all
of these together with their versions should also carry an identifier
and version, and that's what IMAGE_VERSION= and IMAGE_ID= is supposed to
be.

1 files changed, 15 insertions, 5 deletions

diff --git a/man/standard-specifiers.xml b/man/standard-specifiers.xml
index 40bb6cc3ea..f1666365b9 100644
--- a/man/standard-specifiers.xml
+++ b/man/standard-specifiers.xml
@@ -4,16 +4,21 @@
 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
 
 <tbody>
-  <row id='b'>
-    <entry><literal>%b</literal></entry>
-    <entry>Boot ID</entry>
-    <entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
-  </row>
   <row id='a'>
     <entry><literal>%a</literal></entry>
     <entry>Architecture</entry>
     <entry>A short string identifying the architecture of the local system. A string such as <constant>x86</constant>, <constant>x86-64</constant> or <constant>arm64</constant>. See the architectures defined for <varname>ConditionArchitecture=</varname> in <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a full list.</entry>
   </row>
+  <row id='A'>
+    <entry><literal>%A</literal></entry>
+    <entry>Operating system image version</entry>
+    <entry>The operating system image version identifier of the running system, as read from the <varname>IMAGE_VERSION=</varname> field of <filename>/etc/os-release</filename>. If not set, resolves to an empty string. See <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
+  </row>
+  <row id='b'>
+    <entry><literal>%b</literal></entry>
+    <entry>Boot ID</entry>
+    <entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
+  </row>
   <row id='B'>
     <entry><literal>%B</literal></entry>
     <entry>Operating system build ID</entry>
@@ -34,6 +39,11 @@
     <entry>Machine ID</entry>
     <entry>The machine ID of the running system, formatted as string. See <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
   </row>
+  <row id='M'>
+    <entry><literal>%M</literal></entry>
+    <entry>Operating system image identifier</entry>
+    <entry>The operating system image identifier of the running system, as read from the <varname>IMAGE_ID=</varname> field of <filename>/etc/os-release</filename>. If not set, resolves to an empty string. See <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
+  </row>
   <row id='o'>
     <entry><literal>%o</literal></entry>
     <entry>Operating system ID</entry>