pylibfdt: Add functions to set and get properties as strings

It is common to want to set a property to a nul-terminated string in a
device tree. Add python methods to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

pylibfdt/libfdt.i

@@ -589,6 +589,28 @@ class Fdt:
         return check_err(fdt_setprop_u64(self._fdt, nodeoffset, prop_name, val),
                          quiet)
 
+    def setprop_str(self, nodeoffset, prop_name, val, quiet=()):
+        """Set the string value of a property
+
+        The property is set to the string, with a nul terminator added
+
+        Args:
+            nodeoffset: Node offset containing the property to create/update
+            prop_name: Name of property
+            val: Value to write (string without nul terminator). Unicode is
+                supposed by encoding to UTF-8
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Error code, or 0 if OK
+
+        Raises:
+            FdtException if no parent found or other error occurs
+        """
+        val = val.encode('utf-8') + '\0'
+        return check_err(fdt_setprop(self._fdt, nodeoffset, prop_name,
+                                     val, len(val)), quiet)
+
     def delprop(self, nodeoffset, prop_name):
         """Delete a property from a node
 
@@ -646,6 +668,14 @@ class Property(bytearray):
 
     def as_int64(self):
         return self.as_cell('q')
+
+    def as_str(self):
+        """Unicode is supported by decoding from UTF-8"""
+        if self[-1] != 0:
+            raise ValueError('Property lacks nul termination')
+        if 0 in self[:-1]:
+            raise ValueError('Property contains embedded nul characters')
+        return self[:-1].decode('utf-8')
 %}
 
 %rename(fdt_property) fdt_property_func;

tests/pylibfdt_tests.py

@@ -68,6 +68,8 @@ TEST_VALUE64_1L = 0x01abcdef
 TEST_VALUE64_1 = (TEST_VALUE64_1H << 32) | TEST_VALUE64_1L
 
 TEST_STRING_1 = 'hello world'
+TEST_STRING_2 = 'hi world'
+TEST_STRING_3 = u'unicode ' + unichr(467)
 
 
 def get_err(err_code):
@@ -440,6 +442,29 @@ class PyLibfdtTests(unittest.TestCase):
         self.assertEquals(struct.pack('>Q', TEST_VALUE64_1),
                           self.fdt.getprop(node, prop))
 
+    def testSetPropStr(self):
+        """Test that we can set a property to a particular string"""
+        node = 0
+        prop = 'prop-str'
+        self.assertEquals(TEST_STRING_1, self.fdt.getprop(node, prop).as_str())
+        self.fdt.setprop_str(node, prop, TEST_STRING_2)
+        self.assertEquals(TEST_STRING_2, self.fdt.getprop(node, prop).as_str())
+        with self.assertRaises(ValueError) as e:
+            self.fdt.getprop(node, 'prop-int').as_str()
+        self.assertIn('lacks nul termination', str(e.exception))
+
+        node2 = self.fdt.path_offset('/subnode@1/subsubnode')
+        with self.assertRaises(ValueError) as e:
+            self.fdt.getprop(node2, 'compatible').as_str()
+        self.assertIn('embedded nul', str(e.exception))
+
+        # Expand the device tree so we now have room
+        self.fdt.resize(self.fdt.totalsize() + 50)
+        prop = 'prop-unicode'
+        self.fdt.setprop_str(node, prop, TEST_STRING_3)
+        self.assertEquals(TEST_STRING_3,
+                          self.fdt.getprop(node, prop).as_str())
+
 
 if __name__ == "__main__":
     unittest.main()