[PATCH v2 3/3] wic: apply --extra-space + --overhead to squashfs

[Enrico Scholz <enrico.scholz@sigma-chemnitz.de>]

The --extra-space and --overhead option did not had an effect to squashfs
partitions.  Although squashfs is read-only, it can be useful to allocate
more space for the on-disk partition to avoid repartitioning of the whole
disk when a new (and larger) squashfs image is written on later updates.

Patch calls get_rootfs_size() *after* creating the image and truncates
it then.

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
---
 scripts/lib/wic/partition.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/scripts/lib/wic/partition.py b/scripts/lib/wic/partition.py
index b623bb9..bf9bbc3 100644
--- a/scripts/lib/wic/partition.py
+++ b/scripts/lib/wic/partition.py
@@ -195,6 +195,17 @@ class Partition():
                            "larger (%d kB) than its allowed size %d kB" %
                            (self.mountpoint, self.size, self.fixed_size))
 
+    def _extend_rootfs_image(self, rootfs):
+        """Enlarges the rootfs so that it fulfills size/overhead-factor
+        constraints"""
+
+        sz = (os.stat(rootfs).st_size + 1023) // 1024
+        pad_sz = self.get_rootfs_size(sz)
+
+        if pad_sz > sz:
+            with open(rootfs, 'a') as f:
+                os.ftruncate(f.fileno(), pad_sz * 1024)
+
     def prepare_rootfs(self, cr_workdir, oe_builddir, rootfs_dir,
                        native_sysroot):
         """
@@ -338,6 +349,8 @@ class Partition():
                        (rootfs_dir, rootfs, extraopts)
         exec_native_cmd(squashfs_cmd, native_sysroot, pseudo=pseudo)
 
+        self._extend_rootfs_image(rootfs)
+
     def prepare_empty_partition_ext(self, rootfs, oe_builddir,
                                     native_sysroot):
         """
-- 
2.9.5