[initcpiocfg] Allow alternate source file

This is possibly only interesting for testing purposes.

src/modules/initcpiocfg/initcpiocfg.conf

@@ -28,3 +28,11 @@ hooks:
     prepend: [ bogus ]
     append: [ bogus ]
     remove: [ bogus ]
+
+#
+# In some cases, you may want to use a different source
+# file than /etc/mkinitcpio.conf , e.g. because the live system
+# does not match the target in a useful way. If unset or
+# empty, defaults to /etc/mkinitcpio.conf
+#
+source: "/etc/mkinitcpio.conf"

src/modules/initcpiocfg/initcpiocfg.schema.yaml

@@ -14,3 +14,4 @@ properties:
             prepend: { type: array, items: string }
             append: { type: array, items: string }
             remove: { type: array, items: string }
+    source: { type: string }

src/modules/initcpiocfg/main.py

@@ -97,7 +97,7 @@ def get_host_initcpio():
     the lines from that file, or an empty list if it does
     not exist.
     """
-    hostfile = "/etc/mkinitcpio.conf"
+    hostfile = libcalamares.job.configuration.get("source", None) or "/etc/mkinitcpio.conf"
     try:
         with open(hostfile, "r") as mkinitcpio_file:
             mklins = [x.strip() for x in mkinitcpio_file.readlines()]