[PATCH] do_image: Implement IMAGE_ROOTFS_EXCLUDE_PATH feature.

[Kristian Amlie <kristian.amlie@mender.io>]

This is a direct followup from the earlier f6a064d969f414 commit in
wic. It works more or less the same way: The variable specifies a list
of directories relative to the root of the rootfs, and these
directories will be excluded from the resulting rootfs image. If an
entry ends with a slash, only the contents are omitted, not the
directory itself.

Signed-off-by: Kristian Amlie <kristian.amlie@mender.io>
---
 meta/classes/image.bbclass | 73 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 2 deletions(-)

diff --git a/meta/classes/image.bbclass b/meta/classes/image.bbclass
index 405fd73..a309435 100644
--- a/meta/classes/image.bbclass
+++ b/meta/classes/image.bbclass
@@ -496,8 +496,8 @@ python () {
         d.setVar('do_image_%s' % t, '\n'.join(cmds))
         d.setVarFlag('do_image_%s' % t, 'func', '1')
         d.setVarFlag('do_image_%s' % t, 'fakeroot', '1')
-        d.setVarFlag('do_image_%s' % t, 'prefuncs', debug + 'set_image_size')
-        d.setVarFlag('do_image_%s' % t, 'postfuncs', 'create_symlinks')
+        d.setVarFlag('do_image_%s' % t, 'prefuncs', debug + 'set_image_size prepare_excluded_directories')
+        d.setVarFlag('do_image_%s' % t, 'postfuncs', 'create_symlinks cleanup_excluded_directories')
         d.setVarFlag('do_image_%s' % t, 'subimages', ' '.join(subimages))
         d.appendVarFlag('do_image_%s' % t, 'vardeps', ' '.join(vardeps))
         d.appendVarFlag('do_image_%s' % t, 'vardepsexclude', 'DATETIME')
@@ -506,6 +506,75 @@ python () {
         bb.build.addtask('do_image_%s' % t, 'do_image_complete', after, d)
 }
 
+python prepare_excluded_directories() {
+    exclude_var = d.getVar('IMAGE_ROOTFS_EXCLUDE_PATH')
+    if not exclude_var:
+        return
+
+    import shutil
+    from oe.path import copyhardlinktree
+
+    exclude_list = exclude_var.split()
+
+    taskname = d.getVar("BB_CURRENTTASK")
+
+    rootfs_orig = d.getVar('IMAGE_ROOTFS')
+    # We need a new rootfs directory we can delete files from. Copy to
+    # workdir.
+    new_rootfs = os.path.realpath(os.path.join(d.getVar("WORKDIR"), "rootfs.%s" % taskname))
+
+    if os.path.lexists(new_rootfs):
+        shutil.rmtree(os.path.join(new_rootfs))
+
+    copyhardlinktree(rootfs_orig, new_rootfs)
+
+    for orig_path in exclude_list:
+        path = orig_path
+        if os.path.isabs(path):
+            msger.error("IMAGE_ROOTFS_EXCLUDE_PATH: Must be relative: %s" % orig_path)
+
+        full_path = os.path.realpath(os.path.join(new_rootfs, path))
+
+        # Disallow climbing outside of parent directory using '..',
+        # because doing so could be quite disastrous (we will delete the
+        # directory).
+        if not full_path.startswith(new_rootfs):
+            msger.error("'%s' points to a path outside the rootfs" % orig_path)
+
+        if path.endswith(os.sep):
+            # Delete content only.
+            for entry in os.listdir(full_path):
+                full_entry = os.path.join(full_path, entry)
+                if os.path.isdir(full_entry) and not os.path.islink(full_entry):
+                    shutil.rmtree(full_entry)
+                else:
+                    os.remove(full_entry)
+        else:
+            # Delete whole directory.
+            shutil.rmtree(full_path)
+
+    # Save old value for cleanup later.
+    d.setVar('IMAGE_ROOTFS_ORIG', rootfs_orig)
+    d.setVar('IMAGE_ROOTFS', new_rootfs)
+}
+
+python cleanup_excluded_directories() {
+    exclude_var = d.getVar('IMAGE_ROOTFS_EXCLUDE_PATH')
+    if not exclude_var:
+        return
+
+    import shutil
+
+    rootfs_dirs_excluded = d.getVar('IMAGE_ROOTFS')
+    rootfs_orig = d.getVar('IMAGE_ROOTFS_ORIG')
+    # This should never happen, since we should have set it to a different
+    # directory in the prepare function.
+    assert rootfs_dirs_excluded != rootfs_orig
+
+    shutil.rmtree(rootfs_dirs_excluded)
+    d.setVar('IMAGE_ROOTFS', rootfs_orig)
+}
+
 #
 # Compute the rootfs size
 #
-- 
2.7.4