wic: add --extra-partition-space option to set unused space

By default, the content of the partition is filled by the filesystem
without leaving any unused free space. The --extra-space flag adds
extra space to the filesystem size, not to the partition.

Unused free space after the filesystem can be useful for some cases,
such as encrypting a partition at runtime.
With --extra-partition-space 32M, we ensure that the last 32M of the
partition is unused: this space does not contain filesystem data and
can store the LUKS2 header.

The implementation sets a difference between the partition and
filesystem size:
  - With --fixed-size, the extra part space is removed from the
    filesystem size.
  - Otherwise (with or without --size flag), the extra part space is
    added to the partition size.

(From OE-Core rev: 22fd1702aedf40257aa53963b62b5ef1bbd2818a)

Signed-off-by: Pierre-Loup GOSSE <pierre-loup.gosse@smile.fr>

CC: Alexander Kanavin <alex.kanavin@gmail.com>
CC: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/scripts/lib/wic/help.py b/scripts/lib/wic/help.py
index 2e3061f343..800c0abf0f 100644
--- a/scripts/lib/wic/help.py
+++ b/scripts/lib/wic/help.py
@@ -1020,6 +1020,14 @@ DESCRIPTION
                         By default, 10MB. This option cannot be used
                         with --fixed-size option.
 
+         --extra-partition-space: This option is specific to wic. It adds extra
+                                  empty space after the space filled by the
+                                  filesystem. With --fixed-size, the extra
+                                  partition space is removed from the filesystem
+                                  size. Otherwise (with or without --size flag),
+                                  the extra partition space is added to the final
+                                  paritition size. The default value is 0MB.
+
          --overhead-factor: This option is specific to wic. The
                             size of the partition is multiplied by
                             this factor. It has to be greater than or