wic: copy rootfs directory before changing fstab

wic updates /etc/fstab on root partition if there are
valid mount points in .wks

When wic runs from bitbake this can cause incorrect results
or even breakage of other tasks working with the same rootfs
directory in parallel with do_image_wic.

Implemented copying rootfs directory to a temporary location
using copyhardlinktree before updating fstab to avoid conflicts with
other tasks working with the same rootfs directory.

(From OE-Core rev: 92e1c7d47e695eb4ce1a863cd0f6c49dca1c2339)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/plugins/imager/direct.py

@@ -32,6 +32,8 @@ import uuid
 
 from time import strftime
 
+from oe.path import copyhardlinktree
+
 from wic import WicError
 from wic.filemap import sparse_copy
 from wic.ksparser import KickStart, KickStartError
@@ -115,12 +117,18 @@ class DirectPlugin(ImagerPlugin):
             fstab_lines = fstab.readlines()
 
         if self._update_fstab(fstab_lines, self.parts):
-            shutil.copyfile(fstab_path, fstab_path + ".orig")
+            # copy rootfs dir to workdir to update fstab
+            # as rootfs can be used by other tasks and can't be modified
+            new_rootfs = os.path.realpath(os.path.join(self.workdir, "rootfs_copy"))
+            copyhardlinktree(image_rootfs, new_rootfs)
+            fstab_path = os.path.join(new_rootfs, 'etc/fstab')
+
+            os.unlink(fstab_path)
 
             with open(fstab_path, "w") as fstab:
                 fstab.writelines(fstab_lines)
 
-            return fstab_path
+            return new_rootfs
 
     def _update_fstab(self, fstab_lines, parts):
         """Assume partition order same as in wks"""
@@ -156,7 +164,10 @@ class DirectPlugin(ImagerPlugin):
         filesystems from the artifacts directly and combine them into
         a partitioned image.
         """
-        fstab_path = self._write_fstab(self.rootfs_dir.get("ROOTFS_DIR"))
+        new_rootfs = self._write_fstab(self.rootfs_dir.get("ROOTFS_DIR"))
+        if new_rootfs:
+            # rootfs was copied to update fstab
+            self.rootfs_dir['ROOTFS_DIR'] = new_rootfs
 
         for part in self.parts:
             # get rootfs size from bitbake variable if it's not set in .ks file
@@ -172,12 +183,7 @@ class DirectPlugin(ImagerPlugin):
                     if rsize_bb:
                         part.size = int(round(float(rsize_bb)))
 
-        try:
-            self._image.prepare(self)
-        finally:
-            if fstab_path:
-                shutil.move(fstab_path + ".orig", fstab_path)
-
+        self._image.prepare(self)
         self._image.layout_partitions()
         self._image.create()