oeqa/selftest/wic: add test case for sparse images

Add a testcase to build a directdisk image and check that the
used disk size is less than the apparent size, as wic now
assembles images as sparse files.

(From OE-Core rev: 2b8299eb6b911e64d9a05b86c07b489d15eeaa5e)

Signed-off-by: Joshua Lock <joshua.lock@collabora.co.uk>
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/wic.py

@@ -276,3 +276,16 @@ class Wic(oeSelfTest):
             status, output = qemu.run_serial(command)
             self.assertEqual(1, status, 'Failed to run command "%s": %s' % (command, output))
             self.assertEqual(output, '/dev/root /\r\n/dev/vda3 /mnt')
+
+    def test_sparseness(self):
+        """Test that assembled images are sparse; apparent size > disk usage"""
+        self.assertEqual(0, runCmd("wic create directdisk "
+                                   "--image-name core-image-minimal").status)
+        images = glob(self.resultdir + "directdisk-*.direct")
+        self.assertEqual(1, len(images))
+
+        imagestat = os.stat(images.pop())
+        # st_blocks is the "number of 512-byte blocks allocated for file"
+        used = imagestat.st_blocks*512
+        apparent = imagestat.st_size
+        self.assertLess(used, apparent)