wic: Add --change-directory argument

This option allows to specify which part of a rootfs is going to be
included, the same way the -C argument on tar.

Thanks to this option we can make sure the permissions and usernames
on the target partition are respected, and also simplify the creation of
splitted partitons, not neeting to invoke external vars or using .wks.in
files. Eg:

part / --source rootfs --ondisk sda --fstype=ext4 --exclude-path=etc/   
part /etc --source rootfs --fstype=ext4 --change-directory=etc

Cc: Paul Barker <pbarker@konsulko.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 18 insertions, 3 deletions

diff --git a/scripts/lib/wic/plugins/source/rootfs.py b/scripts/lib/wic/plugins/source/rootfs.py
index 8b2a067385..85c634f8a1 100644
--- a/scripts/lib/wic/plugins/source/rootfs.py
+++ b/scripts/lib/wic/plugins/source/rootfs.py
@@ -86,14 +86,29 @@ class RootfsPlugin(SourcePlugin):
         new_rootfs = None
         new_pseudo = None
         # Handle excluded paths.
-        if part.exclude_path or part.include_path:
+        if part.exclude_path or part.include_path or part.change_directory:
             # We need a new rootfs directory we can delete files from. Copy to
             # workdir.
             new_rootfs = os.path.realpath(os.path.join(cr_workdir, "rootfs%d" % part.lineno))
 
             if os.path.lexists(new_rootfs):
                 shutil.rmtree(os.path.join(new_rootfs))
-            copyhardlinktree(part.rootfs_dir, new_rootfs)
+
+            if part.change_directory:
+                cd = part.change_directory
+                if cd[-1] == '/':
+                    cd = cd[:-1]
+                if os.path.isabs(cd):
+                    logger.error("Must be relative: --change-directory=%s" % cd)
+                    sys.exit(1)
+                orig_dir = os.path.realpath(os.path.join(part.rootfs_dir, cd))
+                if not orig_dir.startswith(part.rootfs_dir):
+                    logger.error("'%s' points to a path outside the rootfs" % orig_dir)
+                    sys.exit(1)
+
+            else:
+                orig_dir = part.rootfs_dir
+            copyhardlinktree(orig_dir, new_rootfs)
 
             # Convert the pseudo directory to its new location
             if (pseudo_dir):
@@ -108,7 +123,7 @@ class RootfsPlugin(SourcePlugin):
                 pseudo_cmd = "%s -B -m %s -M %s" % (cls.__get_pseudo(native_sysroot,
                                                                      new_rootfs,
                                                                      new_pseudo),
-                                                    part.rootfs_dir, new_rootfs)
+                                                    orig_dir, new_rootfs)
                 exec_native_cmd(pseudo_cmd, native_sysroot)
 
             for path in part.include_path or []: