Make labeled usb drive/mmc card real optional.

Waiting for the devices, especially, when there are more than one/two o
them is annoying. Let's make a compromise for user to choose hes way for
providing password for key and/or use specific device holding a key.

README.rst

@@ -62,5 +62,13 @@ Usage
   on ``/boot`` with appropriate links. Note, that old images (they have
   ``.old`` suffix in the filename) will be removed in that case.
 
+Using key devices
+-----------------
+
+It is possible to use an SD card (if computer does have reader built-in) or old
+plain USB pendrive. Currently support for the keys is limited to 4096 bytes,
+and assumption that key is unencrypted - it helps with booting system
+non-interactively.
+
 .. _ccrypt: https://sourceforge.net/projects/ccrypt/
 .. _cryptsetup: https://gitlab.com/cryptsetup/cryptsetup/blob/master/README.md

mkinitramfs.py

@@ -314,7 +314,7 @@ class Initramfs(object):
             fobj.write(INIT_CMD)
             if self._args.disk_label:
                 fobj.write(INIT_LABELED % {'label': self._args.disk_label})
-            else:
+            if self._args.sdcard:
                 fobj.write(INIT_SD)
             fobj.write(INIT_OPEN)
         os.chmod('init', 0b111101101)
@@ -429,8 +429,9 @@ def main():
     parser.add_argument('-k', '--key-path', help='path to the location where '
                         'keys are stored', default=KEYS_PATH)
     parser.add_argument('-d', '--disk-label', help='Provide disk label '
-                        'instead of assumed first partition on hardcoded SD '
-                        'card reader')
+                        'to be read decritpion key from.')
+    parser.add_argument('-s', '--sdcard', help='Use built in sdcard reader to '
+                        'read from (hopefully) inserted card')
     parser.add_argument('-l', '--lvm', action='store_true',
                         help='Enable LVM in init.')
     parser.add_argument('disk', choices=disks.keys(), help='Disk name')