kernel-install: support full set of config files and drop-ins

This brings the handling of config for kernel-install in line with most of
systemd, i.e. we search the set of paths for the main config file, and the full
set of drop-in paths for drop-ins.

This mirrors what 07f5e35fe7967c824a87f18a3a1d3c22e5be70f5 did for udev.conf.
That change worked out fine, so I hope this one will too.

The update in the man page is minimal. I think we should split out a separate
page for the config file later on.

One motivating use case is to allow a drop-in to be created for temporary
config overrides and then removed after the operation is done.

1 files changed, 16 insertions, 3 deletions

diff --git a/man/kernel-install.xml b/man/kernel-install.xml
index 519829579f..168776b4d3 100644
--- a/man/kernel-install.xml
+++ b/man/kernel-install.xml
@@ -510,8 +510,12 @@
 
       <para><varname>$KERNEL_INSTALL_CONF_ROOT</varname> can be set to override the location of the
       configuration files read by <command>kernel-install</command>. When set,
-      <filename>install.conf</filename>, <filename>entry-token</filename>, and other files will be
-      read from this directory.</para>
+      <filename>install.conf</filename>, <filename>entry-token</filename>, and other files will be read from
+      this directory only. Note that this path is relative to the host, and in particular <emphasis>symlinks
+      in this directory are resolved relative to the host</emphasis>, even if
+      <option>--root=<replaceable>root</replaceable></option> is used. This means that it is generally
+      <emphasis>not</emphasis> correct to use this variable to specify a directory underneath
+      <replaceable>root</replaceable> if symlinks are used there.</para>
 
       <para><varname>$KERNEL_INSTALL_PLUGINS</varname> can be set to override the list of plugins executed by
       <command>kernel-install</command>. The argument is a whitespace-separated list of paths.
@@ -639,14 +643,23 @@
       </varlistentry>
       <varlistentry>
         <term><filename>/etc/kernel/install.conf</filename></term>
+        <term><filename>/run/kernel/install.conf</filename></term>
+        <term><filename>/usr/local/lib/kernel/install.conf</filename></term>
         <term><filename>/usr/lib/kernel/install.conf</filename></term>
+        <term><filename>/etc/kernel/install.conf.d/*.conf</filename></term>
+        <term><filename>/run/kernel/install.conf.d/*.conf</filename></term>
+        <term><filename>/usr/local/lib/kernel/install.conf.d/*.conf</filename></term>
+        <term><filename>/usr/lib/kernel/install.conf.d/*.conf</filename></term>
         <listitem>
           <para>Configuration file with options for <command>kernel-install</command>, as a series of
           <varname>KEY=</varname><replaceable>VALUE</replaceable> assignments, compatible with shell syntax,
           following the same rules as described in
           <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
           first of the files that is found will be used. <varname>$KERNEL_INSTALL_CONF_ROOT</varname> may be
-          used to override the search path; see below for details.</para>
+          used to override the search path; see below for details. Drop-in files may also be used
+          to extend the configuration with overrides, see
+          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+          </para>
 
           <para>Currently, the following keys are supported:
           <varname>MACHINE_ID=</varname>,