kernel-install/60-ukify: also support the convention with 'devicetree' file

Requested in https://github.com/systemd/systemd/pull/28582#issuecomment-1673300596.
The is the last requested changed, so fixes #28771.

90-loaderentry.install is modified to also check $KERNEL_INSTALL_CONF_ROOT
when looking for the devicetree file. For normal use this is probably not
needed, but it's nice to be consistent and it also makes it much easier to
write the tests.

In tests, also do 'ukify inspect' now that we have it.

src/kernel-install/60-ukify.install.in

@@ -147,6 +147,31 @@ def uki_conf_location() -> Optional[Path]:
                                '/etc/kernel')
 
 
+def devicetree_config_location() -> Optional[Path]:
+    return input_file_location('devicetree')
+
+
+def devicetree_file_location(opts) -> Optional[Path]:
+    # This mirrors the logic in 90-loaderentry.install. Keep in sync.
+    configfile = devicetree_config_location()
+    if configfile is None:
+        return None
+
+    devicetree = configfile.read_text().strip()
+    if not devicetree:
+        raise ValueError(f'{configfile!r} is empty')
+
+    path = input_file_location(
+        devicetree,
+        f'/usr/lib/firmware/{opts.kernel_version}/device-tree',
+        f'/usr/lib/linux-image-{opts.kernel_version}',
+        f'/usr/lib/modules/{opts.kernel_version}/dtb',
+    )
+    if path is None:
+        raise FileNotFoundError(f'DeviceTree file {devicetree} not found')
+    return path
+
+
 def kernel_cmdline_base() -> list[str]:
     path = input_file_location('cmdline')
     if path:
@@ -208,6 +233,9 @@ def call_ukify(opts):
     # Note that 'uki.efi' is the name required by 90-uki-copy.install.
     opts2.output = opts.staging_area / 'uki.efi'
 
+    if devicetree := devicetree_file_location(opts):
+        opts2.devicetree = devicetree
+
     opts2.cmdline = kernel_cmdline(opts)
     if BOOT_STUB:
         opts2.stub = BOOT_STUB

src/kernel-install/90-loaderentry.install.in

@@ -126,10 +126,12 @@ elif [ -f /usr/lib/kernel/devicetree ]; then
 fi
 if [ -n "$DEVICETREE" ]; then
     for prefix in \
+        "$KERNEL_INSTALL_CONF_ROOT" \
         "/usr/lib/firmware/$KERNEL_VERSION/device-tree" \
         "/usr/lib/linux-image-$KERNEL_VERSION" \
         "/usr/lib/modules/$KERNEL_VERSION/dtb"
     do
+        [ -n "$prefix" ] || continue
         [ -f "$prefix/$DEVICETREE" ] || continue
         DEVICETREE_SRC="$prefix/$DEVICETREE"
         break

src/kernel-install/test-kernel-install.sh

@@ -39,6 +39,11 @@ BOOT_ROOT="$D/badboot"
 MACHINE_ID=badbadbadbadbadbad6abadbadbadbad
 EOF
 
+# Create a 'devicetree' config file that points to a fake dtb file
+echo 'subdir/whatever.dtb' >"$D/sources/devicetree"
+mkdir "$D/sources/subdir"
+echo 'DTBDTBDTBDTB' >"$D/sources/subdir/whatever.dtb"
+
 export KERNEL_INSTALL_CONF_ROOT="$D/sources"
 # We "install" multiple plugins, but control which ones will be active via install.conf.
 export KERNEL_INSTALL_PLUGINS="${ukify_install} ${loaderentry_install} ${uki_copy_install}"
@@ -60,9 +65,11 @@ grep -qE '^version +1.1.1' "$entry"
 grep -qE '^options +opt1 opt2' "$entry"
 grep -qE '^linux .*/the-token/1.1.1/linux' "$entry"
 grep -qE '^initrd .*/the-token/1.1.1/initrd' "$entry"
+grep -qE '^devicetree .*/the-token/1.1.1/whatever.dtb' "$entry"
 
 grep -qE 'image' "$BOOT_ROOT/the-token/1.1.1/linux"
 grep -qE 'initrd' "$BOOT_ROOT/the-token/1.1.1/initrd"
+grep -qE 'DTBDTB' "$BOOT_ROOT/the-token/1.1.1/whatever.dtb"
 
 "$kernel_install" inspect
 "$kernel_install" inspect "$D/sources/linux"
@@ -95,9 +102,11 @@ grep -qE '^version +1.1.2' "$entry"
 grep -qE '^options +opt1 opt2' "$entry"
 grep -qE '^linux .*/the-token/1.1.2/linux' "$entry"
 ( ! grep -qE '^initrd' "$entry" )
+grep -qE '^devicetree .*/the-token/1.1.2/whatever.dtb' "$entry"
 
 grep -qE 'image' "$BOOT_ROOT/the-token/1.1.2/linux"
 test ! -e "$BOOT_ROOT/the-token/1.1.2/initrd"
+grep -qE 'DTBDTB' "$BOOT_ROOT/the-token/1.1.2/whatever.dtb"
 
 # Check installation with boot counting
 echo '56' >"$D/sources/tries"
@@ -120,6 +129,7 @@ if [ -f "$ukify" ]; then
 layout=uki
 uki_generator=ukify
 EOF
+
     "$kernel_install" -v add 1.1.3 "$D/sources/linux" "$D/sources/initrd"
     uki="${BOOT_ROOT}/EFI/Linux/the-token-1.1.3+56.efi"
     test -f "$uki"
@@ -129,6 +139,13 @@ EOF
         "$bootctl" kernel-inspect "$uki" | grep -qE 'Version: +1\.1\.3$'
         "$bootctl" kernel-inspect "$uki" | grep -qE 'Cmdline: +opt1 opt2$'
     fi
+
+    "$ukify" inspect "$uki" | grep -qE '^.sbat'
+    "$ukify" inspect "$uki" | grep -qE '^.cmdline'
+    "$ukify" inspect "$uki" | grep -qE '^.uname'
+    "$ukify" inspect "$uki" | grep -qE '^.initrd'
+    "$ukify" inspect "$uki" | grep -qE '^.linux'
+    "$ukify" inspect "$uki" | grep -qE '^.dtb'
 fi
 
 # Test bootctl