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>

3 files changed, 32 insertions, 13 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
diff --git a/scripts/lib/wic/ksparser.py b/scripts/lib/wic/ksparser.py
index 596b6e8e7e..a1aaf1b4b3 100644
--- a/scripts/lib/wic/ksparser.py
+++ b/scripts/lib/wic/ksparser.py
@@ -154,6 +154,7 @@ class KickStart():
         part.add_argument('--include-path', nargs='+', action='append')
         part.add_argument('--change-directory')
         part.add_argument("--extra-space", type=sizetype("M"))
+        part.add_argument('--extra-partition-space', type=sizetype("M"))
         part.add_argument('--fsoptions', dest='fsopts')
         part.add_argument('--fspassno', dest='fspassno')
         part.add_argument('--fstype', default='vfat',
@@ -259,6 +260,8 @@ class KickStart():
                             err = "%s:%d: Must set the label with --label" \
                                   % (confpath, lineno)
                             raise KickStartError(err)
+                        if not parsed.extra_partition_space:
+                            parsed.extra_partition_space = 0
                         # using ArgumentParser one cannot easily tell if option
                         # was passed as argument, if said option has a default
                         # value; --overhead-factor/--extra-space cannot be used
diff --git a/scripts/lib/wic/partition.py b/scripts/lib/wic/partition.py
index b34691d313..d358aabbd6 100644
--- a/scripts/lib/wic/partition.py
+++ b/scripts/lib/wic/partition.py
@@ -29,6 +29,7 @@ class Partition():
         self.disk = args.disk
         self.device = None
         self.extra_space = args.extra_space
+        self.extra_partition_space = args.extra_partition_space
         self.exclude_path = args.exclude_path
         self.include_path = args.include_path
         self.change_directory = args.change_directory
@@ -91,13 +92,12 @@ class Partition():
     def get_rootfs_size(self, actual_rootfs_size=0):
         """
         Calculate the required size of rootfs taking into consideration
-        --size/--fixed-size flags as well as overhead and extra space, as
-        specified in kickstart file. Raises an error if the
-        `actual_rootfs_size` is larger than fixed-size rootfs.
-
+        --size/--fixed-size and --extra-partition-space flags as well as overhead
+        and extra space, as specified in kickstart file. Raises an error
+        if the `actual_rootfs_size` is larger than fixed-size rootfs.
         """
         if self.fixed_size:
-            rootfs_size = self.fixed_size
+            rootfs_size = self.fixed_size - self.extra_partition_space
             if actual_rootfs_size > rootfs_size:
                 raise WicError("Actual rootfs size (%d kB) is larger than "
                                "allowed size %d kB" %
@@ -119,10 +119,18 @@ class Partition():
     def disk_size(self):
         """
         Obtain on-disk size of partition taking into consideration
-        --size/--fixed-size options.
+        --size/--fixed-size and --extra-partition-space options.
+
+        """
+        return self.fixed_size if self.fixed_size else self.size + self.extra_partition_space
 
+    @property
+    def fs_size(self):
+        """
+        Obtain on-disk size of filesystem inside the partition taking into
+        consideration --size/--fixed-size and --extra-partition-space options.
         """
-        return self.fixed_size if self.fixed_size else self.size
+        return self.fixed_size - self.extra_partition_space if self.fixed_size else self.size
 
     def prepare(self, creator, cr_workdir, oe_builddir, rootfs_dir,
                 bootimg_dir, kernel_dir, native_sysroot, updated_fstab_path):
@@ -202,10 +210,10 @@ class Partition():
                            "This a bug in source plugin %s and needs to be fixed." %
                            (self.mountpoint, self.source))
 
-        if self.fixed_size and self.size > self.fixed_size:
+        if self.fixed_size and self.size + self.extra_partition_space > self.fixed_size:
             raise WicError("File system image of partition %s is "
-                           "larger (%d kB) than its allowed size %d kB" %
-                           (self.mountpoint, self.size, self.fixed_size))
+                           "larger (%d kB + %d kB extra part space) than its allowed size %d kB" %
+                           (self.mountpoint, self.size, self.extra_partition_space, self.fixed_size))
 
     def prepare_rootfs(self, cr_workdir, oe_builddir, rootfs_dir,
                        native_sysroot, real_rootfs = True, pseudo_dir = None):
@@ -440,7 +448,7 @@ class Partition():
         """
         Prepare an empty ext2/3/4 partition.
         """
-        size = self.disk_size
+        size = self.fs_size
         with open(rootfs, 'w') as sparse:
             os.ftruncate(sparse.fileno(), size * 1024)
 
@@ -464,7 +472,7 @@ class Partition():
         """
         Prepare an empty btrfs partition.
         """
-        size = self.disk_size
+        size = self.fs_size
         with open(rootfs, 'w') as sparse:
             os.ftruncate(sparse.fileno(), size * 1024)
 
@@ -482,7 +490,7 @@ class Partition():
         """
         Prepare an empty vfat partition.
         """
-        blocks = self.disk_size
+        blocks = self.fs_size
 
         label_str = "-n boot"
         if self.label: