kernel-install: replace 00-entry-directory with K_I_LAYOUT in k-i

341890de866f2ee34919a47ce3fc6c8cd3c1924c made "bootctl install" create
ESP\MID, in preparation of cf73f650890b56a59bfb713c4c82b4e29daa7316 that
followed it and created 00-entry-directory.install to make ESP\MID\KVER
if ESP\MID existed ‒ this meant that "bootctl install" followed by
"kernel-install $(uname -r) /boot/vml*$(uname -r) /boot/ini*$(uname -r)"
actually installed the kernel correctly.

Later, 31e57550b552e113bd3d44355b237c41e42beb58 reverted the first
commit, meaning, that now running those two commands first installs
sd-boot, but then does nothing. Everything appears to work right,
nothing errors out, but no changes are actually done. To the untrained
eye (all of them), even running with -v appears to work:
all the hooks are run, as is depmod, but, again, nothing happens.

This is horrible. Nothing in either manpage suggests what to do
(nor should it, really), but the user is left with a bootloader that
appears fully funxional, since nothing suggests a failure in the output,
but with an unbootable machine, /no way to boot it/, even if they drop
to an EFI shell, since the boot bundle isn't present on the ESP,
and no real recourse even if they boot into a recovery system,
apart from installing like GRUB or whatever.

00- is purely instrumentation for 90-,
and separating one from the other has led to downstream dissatisfaxion
(indeed, the last mentioned commit cited cited exactly that as the
 reversion reason), while creating $ENTRY_DIR_ABS is only required
for bootloaders using the BLS, and shouldn't itself toggle anything.

To that end, introduce an /{e,l}/k/install.conf file that allows
overriding the detected layout, and detect it as "bls" if
$BOOT_ROOT/$MACHINE_ID ($ENTRY_DIR_ABS/..) exists, otherwise "other" ‒
if a user wishes to select a different bootloader,
like GRUB, they (or, indeed, the postinst script) can specify
layout=grub. This disables 90- and $ENTRY_DIR_ABS manipulation.

7 files changed, 116 insertions, 70 deletions

diff --git a/man/kernel-install.xml b/man/kernel-install.xml
index c6414b13dd..83255bb932 100644
--- a/man/kernel-install.xml
+++ b/man/kernel-install.xml
@@ -71,23 +71,21 @@
           <programlisting>add <replaceable>KERNEL-VERSION</replaceable> <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename> <replaceable>KERNEL-IMAGE</replaceable> [<replaceable>INITRD-FILE</replaceable> ...]</programlisting>
           </para>
 
-          <para>Three default plugins execute the following operations in this case:</para>
+          <para>Two default plugins execute the following operations in this case:</para>
 
           <itemizedlist>
-            <listitem><para><filename>00-entry-directory.install</filename> creates the directory
-            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
-            if <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/</filename> already exists.
-            </para></listitem>
+            <listitem><para><command>kernel-install</command> creates
+            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable></filename>,
+            if enabled (see <varname>$KERNEL_INSTALL_LAYOUT=</varname>).</para></listitem>
 
             <listitem><para><filename>50-depmod.install</filename> runs
             <citerefentry project='man-pages'><refentrytitle>depmod</refentrytitle><manvolnum>8</manvolnum></citerefentry> for the
             <replaceable>KERNEL-VERSION</replaceable>.</para></listitem>
 
-            <listitem><para><filename>90-loaderentry.install</filename> copies <replaceable>KERNEL-IMAGE</replaceable>
-            to
+            <listitem><para><filename>90-loaderentry.install</filename>
+            copies <replaceable>KERNEL-IMAGE</replaceable> to
             <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/linux</filename>.
-            If an <replaceable>INITRD-FILE</replaceable> is provided, it also copies <replaceable>INITRD-FILE</replaceable>
-            to
+            If <replaceable>INITRD-FILE</replaceable>s are provided, it also copies them to
             <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL_VERSION</replaceable>/<replaceable>INITRD-FILE</replaceable></filename>.
             It also creates a boot loader entry according to the <ulink
             url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> in
@@ -96,9 +94,7 @@
             <filename>/etc/os-release</filename> or <filename>/usr/lib/os-release</filename> (if the former is
             missing), or "Linux <replaceable>KERNEL-VERSION</replaceable>", if unset.</para>
 
-            <para>If the entry directory
-            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename>
-            does not exist, this plugin does nothing.</para></listitem>
+            <para>If <varname>$KERNEL_INSTALL_LAYOUT=</varname> is not "bls", this plugin does nothing.</para></listitem>
           </itemizedlist>
         </listitem>
       </varlistentry>
@@ -119,13 +115,15 @@
           <para>Two default plugins execute the following operations in this case:</para>
 
           <itemizedlist>
-
             <listitem><para><filename>50-depmod.install</filename> removes the files generated by <command>depmod</command> for this kernel again.</para></listitem>
 
             <listitem><para><filename>90-loaderentry.install</filename> removes the file
             <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>.conf</filename>.</para></listitem>
-          </itemizedlist>
 
+            <listitem><para><command>kernel-install</command> removes
+            <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable></filename>,
+            if enabled (see <varname>$KERNEL_INSTALL_LAYOUT=</varname>).</para></listitem>
+          </itemizedlist>
         </listitem>
       </varlistentry>
 
@@ -172,6 +170,30 @@
     either 32 hexadecimal characters or the special value <literal>Default</literal>.</para>
     <para><varname>KERNEL_INSTALL_BOOT_ROOT=</varname> is set for the plugins to the root directory (mount point, usually) of the hierarchy
     where boot-loader entries, kernel images, and associated resources should be placed. Can be overridden by setting <varname>BOOT_ROOT=</varname>.</para>
+
+    <para><varname>KERNEL_INSTALL_LAYOUT=bls|other|...</varname> specifies the installation layout.
+    Defaults to <option>bls</option> if <filename>$BOOT/<replaceable>MACHINE-ID</replaceable></filename> exists, or <option>other</option> otherwise.
+    Additional layout names may be defined by convention. If a plugin uses a special layout,
+    it's encouraged to declare its own layout name and configure <varname>layout=</varname> in <filename>install.conf</filename> upon initial installation.</para>
+
+    <variablelist>
+      <varlistentry>
+        <term>bls</term>
+        <listitem>
+          <para>Standard <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> layout,
+          compatible with <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>: entries in
+          <filename>$BOOT/loader/entries/<replaceable>MACHINE-ID</replaceable>-<replaceable>KERNEL-VERSION</replaceable>[+<replaceable>TRIES</replaceable>].conf</filename>,
+          kernel and initrds under <filename>$BOOT/<replaceable>MACHINE-ID</replaceable>/<replaceable>KERNEL-VERSION</replaceable>/</filename></para>
+          <para>Provided by <filename>90-loaderentry.install</filename>.</para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>other</term>
+        <listitem>
+          <para>Some other layout not understood natively by <command>kernel-install</command>.</para>
+        </listitem>
+      </varlistentry>
+    </variablelist>
   </refsect1>
 
   <refsect1>
@@ -251,6 +273,18 @@
             Otherwise, <literal>Linux <replaceable>KERNEL-VERSION</replaceable></literal> will be used.</para>
           </listitem>
       </varlistentry>
+      <varlistentry>
+        <term>
+          <filename>/usr/lib/kernel/install.conf</filename>
+          <filename>/etc/kernel/install.conf</filename>
+        </term>
+          <listitem>
+            <para>Configuration options for <command>kernel-install</command>,
+            as a series of <varname>KEY=</varname><replaceable>VALUE</replaceable> assignments,
+            compatible with shell syntax.
+            See the Environment variables section for supported keys.</para>
+          </listitem>
+      </varlistentry>
     </variablelist>
   </refsect1>
 
diff --git a/meson.build b/meson.build
index db50f92512..0e8f58eb24 100644
--- a/meson.build
+++ b/meson.build
@@ -171,7 +171,8 @@ udevlibexecdir = rootprefixdir / 'lib/udev'
 udevrulesdir = udevlibexecdir / 'rules.d'
 udevhwdbdir = udevlibexecdir / 'hwdb.d'
 catalogdir = prefixdir / 'lib/systemd/catalog'
-kernelinstalldir = prefixdir / 'lib/kernel/install.d'
+kerneldir = prefixdir / 'lib/kernel'
+kernelinstalldir = kerneldir / 'install.d'
 factorydir = datadir / 'factory'
 bootlibdir = prefixdir / 'lib/systemd/boot/efi'
 testsdir = prefixdir / 'lib/systemd/tests'
diff --git a/src/kernel-install/00-entry-directory.install b/src/kernel-install/00-entry-directory.install
deleted file mode 100644
index 5576179d52..0000000000
--- a/src/kernel-install/00-entry-directory.install
+++ /dev/null
@@ -1,47 +0,0 @@
-#!/usr/bin/env bash
-# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
-# ex: ts=8 sw=4 sts=4 et filetype=sh
-# SPDX-License-Identifier: LGPL-2.1-or-later
-#
-# 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.
-#
-# systemd is distributed in the hope that it will be useful, but
-# WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-# General Public License for more details.
-#
-# You should have received a copy of the GNU Lesser General Public License
-# along with systemd; If not, see <http://www.gnu.org/licenses/>.
-
-COMMAND="$1"
-KERNEL_VERSION="$2"
-ENTRY_DIR_ABS="$3"
-KERNEL_IMAGE="$4"
-INITRD_OPTIONS_START="5"
-
-if ! [[ $KERNEL_INSTALL_MACHINE_ID ]]; then
-    exit 0
-fi
-
-if [[ $COMMAND != add ]]; then
-    exit 0
-fi
-
-# Create the entry directory if its parent exists ‒
-# this is an administrative decision and the only function of this plugin.
-MACHINE_ID_DIR="$KERNEL_INSTALL_BOOT_ROOT/$KERNEL_INSTALL_MACHINE_ID"
-if ! [ -d "$MACHINE_ID_DIR" ]; then
-    exit 0
-fi
-
-if [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ]; then
-    echo "+mkdir -v -p $ENTRY_DIR_ABS"
-    exec mkdir -v -p "$ENTRY_DIR_ABS"
-else
-    exec mkdir -p "$ENTRY_DIR_ABS"
-fi
diff --git a/src/kernel-install/90-loaderentry.install b/src/kernel-install/90-loaderentry.install
index a4dba1396d..044eced3f0 100644
--- a/src/kernel-install/90-loaderentry.install
+++ b/src/kernel-install/90-loaderentry.install
@@ -28,7 +28,7 @@ if ! [[ $KERNEL_INSTALL_MACHINE_ID ]]; then
     exit 0
 fi
 
-if ! [[ -d "$ENTRY_DIR_ABS" ]]; then
+if [ "$KERNEL_INSTALL_LAYOUT" != "bls" ]; then
     exit 0
 fi
 
@@ -92,6 +92,15 @@ else
     LOADER_ENTRY="$BOOT_ROOT/loader/entries/$MACHINE_ID-$KERNEL_VERSION.conf"
 fi
 
+if ! [ -d "$ENTRY_DIR_ABS" ]; then
+    if [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ]; then
+        echo "+mkdir -v -p $ENTRY_DIR_ABS"
+        mkdir -v -p "$ENTRY_DIR_ABS"
+    else
+        mkdir -p "$ENTRY_DIR_ABS"
+    fi
+fi
+
 install -g root -o root -m 0644 "$KERNEL_IMAGE" "$ENTRY_DIR_ABS/linux" || {
     echo "Could not copy '$KERNEL_IMAGE' to '$ENTRY_DIR_ABS/linux'." >&2
     exit 1
diff --git a/src/kernel-install/install.conf b/src/kernel-install/install.conf
new file mode 100644
index 0000000000..e4802e6fae
--- /dev/null
+++ b/src/kernel-install/install.conf
@@ -0,0 +1,10 @@
+#  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.
+#
+# See kernel-install(8) for details.
+
+#layout=bls|other|...
diff --git a/src/kernel-install/kernel-install b/src/kernel-install/kernel-install
index 103b44ebda..b358b03b2f 100755
--- a/src/kernel-install/kernel-install
+++ b/src/kernel-install/kernel-install
@@ -90,6 +90,12 @@ if [[ ! $COMMAND ]] || [[ ! $KERNEL_VERSION ]]; then
     exit 1
 fi
 
+if [ -r "/etc/kernel/install.conf" ]; then
+    . /etc/kernel/install.conf
+elif [ -r "/usr/lib/kernel/install.conf" ]; then
+    . /usr/lib/kernel/install.conf
+fi
+
 # Prefer to use an existing machine ID from /etc/machine-info or /etc/machine-id. If we're using the machine
 # ID /etc/machine-id, try to persist it in /etc/machine-info. If no machine ID is found, try to generate
 # a new machine ID in /etc/machine-info. If that fails, use "Default".
@@ -124,6 +130,26 @@ ENTRY_DIR_ABS="$BOOT_ROOT/$MACHINE_ID/$KERNEL_VERSION"
 export KERNEL_INSTALL_MACHINE_ID="$MACHINE_ID"
 export KERNEL_INSTALL_BOOT_ROOT="$BOOT_ROOT"
 
+if [ -z "$layout" ]; then
+    # Administrative decision: if not present, some scripts generate into /boot.
+    if [ -d "$BOOT_ROOT/$MACHINE_ID" ]; then
+        layout="bls"
+    else
+        layout="other"
+    fi
+fi
+
+
+ENTRY_DIR_ABS="$BOOT_ROOT/$MACHINE_ID/$KERNEL_VERSION"
+
+export KERNEL_INSTALL_MACHINE_ID="$MACHINE_ID"
+export KERNEL_INSTALL_BOOT_ROOT="$BOOT_ROOT"
+export KERNEL_INSTALL_LAYOUT="$layout"
+
+[ "$layout" = "bls" ]
+MAKE_ENTRY_DIR_ABS=$?
+
+
 ret=0
 
 readarray -t PLUGINS <<<"$(
@@ -144,6 +170,18 @@ case $COMMAND in
             exit 1
         fi
 
+        if [ "$MAKE_ENTRY_DIR_ABS" -eq 0 ]; then
+            # Compatibility with earlier versions that used the presence of $BOOT_ROOT/$MACHINE_ID
+            # to signal to 00-entry-directory to create $ENTRY_DIR_ABS
+            # to serve as the indication to use or to not use the BLS
+            if [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ]; then
+                echo "+mkdir -v -p $ENTRY_DIR_ABS"
+                mkdir -v -p "$ENTRY_DIR_ABS"
+            else
+                mkdir -p "$ENTRY_DIR_ABS"
+            fi
+        fi
+
         for f in "${PLUGINS[@]}"; do
             if [[ -x $f ]]; then
                 [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && \
@@ -172,11 +210,10 @@ case $COMMAND in
             fi
         done
 
-        [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && \
-            echo "Removing $ENTRY_DIR_ABS"
-
-        rm -rf "$ENTRY_DIR_ABS"
-        ((ret+=$?))
+        if [ "$MAKE_ENTRY_DIR_ABS" -eq 0 ]; then
+            [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && echo "Removing $ENTRY_DIR_ABS/"
+            rm -rf "$ENTRY_DIR_ABS"
+        fi
         ;;
 
     *)
diff --git a/src/kernel-install/meson.build b/src/kernel-install/meson.build
index 893832461e..508058f1cf 100644
--- a/src/kernel-install/meson.build
+++ b/src/kernel-install/meson.build
@@ -7,12 +7,14 @@ if want_kernel_install
                      install_mode : 'rwxr-xr-x',
                      install_dir : bindir)
 
-        install_data('00-entry-directory.install',
-                     '50-depmod.install',
+        install_data('50-depmod.install',
                      '90-loaderentry.install',
                      install_mode : 'rwxr-xr-x',
                      install_dir : kernelinstalldir)
 
+        install_data('install.conf',
+                     install_dir : kerneldir)
+
         if install_sysconfdir
                 meson.add_install_script('sh', '-c',
                                          mkdir_p.format(sysconfdir / 'kernel/install.d'))