meson: make net.naming-scheme= default configurable

This is useful for distributions, where the stability of interface names should
be preseved after an upgrade of systemd. So when some specific release of the
distro is made available, systemd defaults to the latest & greatest naming
scheme, and subsequent updates set the same default. This default may still
be overriden through the kernel and env var options.

A special value "latest" is also allowed. Without a specific name, it is harder
to verride from meson. In case of 'combo' options, meson reads the default
during the initial configuration, and "remembers" this choice. When systemd is
updated, old build/ directories could keep the old default, which would be
annoying. Hence, "latest" is introduced to make it explicit, yet follow the
upstream. This is actually useful for the user too, because it may be used
as an override, without having to actually specify a version.

1 files changed, 14 insertions, 10 deletions

diff --git a/man/systemd-udevd.service.xml b/man/systemd-udevd.service.xml
index b1409698a..330700d7d 100644
--- a/man/systemd-udevd.service.xml
+++ b/man/systemd-udevd.service.xml
@@ -174,16 +174,20 @@
         <term><varname>net.naming-scheme=</varname></term>
         <listitem>
           <para>Network interfaces are renamed to give them predictable names when possible (unless
-          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various device metadata
-          fields. Newer versions of <filename>systemd-udevd.service</filename> take more of these fields into account,
-          improving (and thus possibly changing) the names used for the same devices. With this kernel command line
-          option it is possible to pick a specific version of this algorithm. It expects a naming scheme identifier as
-          argument. Currently the following identifiers are known: <literal>v238</literal>, <literal>v239</literal>,
-          <literal>v240</literal> which each implement the naming scheme that was the default in the indicated systemd
-          version. Note that selecting a specific scheme is not sufficient to fully stabilize interface naming: the
-          naming is generally derived from driver attributes exposed by the kernel. As the kernel is updated,
-          previously missing attributes <filename>systemd-udevd.service</filename> is checking might appear, which
-          affects older name derivation algorithms, too.</para>
+          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
+          device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
+          these fields into account, improving (and thus possibly changing) the names used for the same
+          devices. With this kernel command line option it is possible to pick a specific version of this
+          algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
+          are known: <literal>v238</literal>, <literal>v239</literal>, <literal>v240</literal> which each
+          implement the naming scheme that was the default in the indicated systemd version. In addition,
+          <literal>latest</literal> may be used to designate the latest scheme known (to this particular
+          version of <filename>systemd-udevd.service</filename>).</para>
+
+          <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
+          the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
+          updated, previously missing attributes <filename>systemd-udevd.service</filename> is checking might
+          appear, which affects older name derivation algorithms, too.</para>
         </listitem>
       </varlistentry>
     </variablelist>