diff --git a/bitbake/lib/bb/COW.py b/bitbake/lib/bb/COW.py
new file mode 100644
index 0000000..6917ec3
--- /dev/null
+++ b/bitbake/lib/bb/COW.py
@@ -0,0 +1,323 @@
+# ex:ts=4:sw=4:sts=4:et
+# -*- tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*-
+#
+# This is a copy on write dictionary and set which abuses classes to try and be nice and fast.
+#
+# Copyright (C) 2006 Tim Amsell
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+#Please Note:
+# Be careful when using mutable types (ie Dict and Lists) - operations involving these are SLOW.
+# Assign a file to __warn__ to get warnings about slow operations.
+#
+
+from __future__ import print_function
+import copy
+import types
+ImmutableTypes = (
+    types.NoneType,
+    bool,
+    complex,
+    float,
+    int,
+    long,
+    tuple,
+    frozenset,
+    basestring
+)
+
+MUTABLE = "__mutable__"
+
+class COWMeta(type):
+    pass
+
+class COWDictMeta(COWMeta):
+    __warn__ = False
+    __hasmutable__ = False
+    __marker__ = tuple()
+
+    def __str__(cls):
+        # FIXME: I have magic numbers!
+        return "<COWDict Level: %i Current Keys: %i>" % (cls.__count__, len(cls.__dict__) - 3)
+    __repr__ = __str__
+
+    def cow(cls):
+        class C(cls):
+            __count__ = cls.__count__ + 1
+        return C
+    copy = cow
+    __call__ = cow
+
+    def __setitem__(cls, key, value):
+        if not isinstance(value, ImmutableTypes):
+            if not isinstance(value, COWMeta):
+                cls.__hasmutable__ = True
+            key += MUTABLE
+        setattr(cls, key, value)
+
+    def __getmutable__(cls, key, readonly=False):
+        nkey = key + MUTABLE
+        try:
+            return cls.__dict__[nkey]
+        except KeyError:
+            pass
+
+        value = getattr(cls, nkey)
+        if readonly:
+            return value
+
+        if not cls.__warn__ is False and not isinstance(value, COWMeta):
+            print("Warning: Doing a copy because %s is a mutable type." % key, file=cls.__warn__)
+        try:
+            value = value.copy()
+        except AttributeError as e:
+            value = copy.copy(value)
+        setattr(cls, nkey, value)
+        return value
+
+    __getmarker__ = []
+    def __getreadonly__(cls, key, default=__getmarker__):
+        """\
+        Get a value (even if mutable) which you promise not to change.
+        """
+        return cls.__getitem__(key, default, True)
+
+    def __getitem__(cls, key, default=__getmarker__, readonly=False):
+        try:
+            try:
+                value = getattr(cls, key)
+            except AttributeError:
+                value = cls.__getmutable__(key, readonly)
+
+            # This is for values which have been deleted
+            if value is cls.__marker__:
+                raise AttributeError("key %s does not exist." % key)
+
+            return value
+        except AttributeError as e:
+            if not default is cls.__getmarker__:
+                return default
+
+            raise KeyError(str(e))
+
+    def __delitem__(cls, key):
+        cls.__setitem__(key, cls.__marker__)
+
+    def __revertitem__(cls, key):
+        if not cls.__dict__.has_key(key):
+            key += MUTABLE
+        delattr(cls, key)
+
+    def __contains__(cls, key):
+        return cls.has_key(key)
+
+    def has_key(cls, key):
+        value = cls.__getreadonly__(key, cls.__marker__)
+        if value is cls.__marker__:
+            return False
+        return True
+
+    def iter(cls, type, readonly=False):
+        for key in dir(cls):
+            if key.startswith("__"):
+                continue
+
+            if key.endswith(MUTABLE):
+                key = key[:-len(MUTABLE)]
+
+            if type == "keys":
+                yield key
+
+            try:
+                if readonly:
+                    value = cls.__getreadonly__(key)
+                else:
+                    value = cls[key]
+            except KeyError:
+                continue
+
+            if type == "values":
+                yield value
+            if type == "items":
+                yield (key, value)
+        raise StopIteration()
+
+    def iterkeys(cls):
+        return cls.iter("keys")
+    def itervalues(cls, readonly=False):
+        if not cls.__warn__ is False and cls.__hasmutable__ and readonly is False:
+            print("Warning: If you arn't going to change any of the values call with True.", file=cls.__warn__)
+        return cls.iter("values", readonly)
+    def iteritems(cls, readonly=False):
+        if not cls.__warn__ is False and cls.__hasmutable__ and readonly is False:
+            print("Warning: If you arn't going to change any of the values call with True.", file=cls.__warn__)
+        return cls.iter("items", readonly)
+
+class COWSetMeta(COWDictMeta):
+    def __str__(cls):
+        # FIXME: I have magic numbers!
+        return "<COWSet Level: %i Current Keys: %i>" % (cls.__count__, len(cls.__dict__) -3)
+    __repr__ = __str__
+
+    def cow(cls):
+        class C(cls):
+            __count__ = cls.__count__ + 1
+        return C
+
+    def add(cls, value):
+        COWDictMeta.__setitem__(cls, repr(hash(value)), value)
+
+    def remove(cls, value):
+        COWDictMeta.__delitem__(cls, repr(hash(value)))
+
+    def __in__(cls, value):
+        return COWDictMeta.has_key(repr(hash(value)))
+
+    def iterkeys(cls):
+        raise TypeError("sets don't have keys")
+
+    def iteritems(cls):
+        raise TypeError("sets don't have 'items'")
+
+# These are the actual classes you use!
+class COWDictBase(object):
+    __metaclass__ = COWDictMeta
+    __count__ = 0
+
+class COWSetBase(object):
+    __metaclass__ = COWSetMeta
+    __count__ = 0
+
+if __name__ == "__main__":
+    import sys
+    COWDictBase.__warn__ = sys.stderr
+    a = COWDictBase()
+    print("a", a)
+
+    a['a'] = 'a'
+    a['b'] = 'b'
+    a['dict'] = {}
+
+    b = a.copy()
+    print("b", b)
+    b['c'] = 'b'
+
+    print()
+
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems():
+        print(x)
+    print()
+
+    b['dict']['a'] = 'b'
+    b['a'] = 'c'
+
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems():
+        print(x)
+    print()
+
+    try:
+        b['dict2']
+    except KeyError as e:
+        print("Okay!")
+
+    a['set'] = COWSetBase()
+    a['set'].add("o1")
+    a['set'].add("o1")
+    a['set'].add("o2")
+
+    print("a", a)
+    for x in a['set'].itervalues():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b['set'].itervalues():
+        print(x)
+    print()
+
+    b['set'].add('o3')
+
+    print("a", a)
+    for x in a['set'].itervalues():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b['set'].itervalues():
+        print(x)
+    print()
+
+    a['set2'] = set()
+    a['set2'].add("o1")
+    a['set2'].add("o1")
+    a['set2'].add("o2")
+
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems(readonly=True):
+        print(x)
+    print()
+
+    del b['b']
+    try:
+        print(b['b'])
+    except KeyError:
+        print("Yay! deleted key raises error")
+
+    if b.has_key('b'):
+        print("Boo!")
+    else:
+        print("Yay - has_key with delete works!")
+
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems(readonly=True):
+        print(x)
+    print()
+
+    b.__revertitem__('b')
+
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems(readonly=True):
+        print(x)
+    print()
+
+    b.__revertitem__('dict')
+    print("a", a)
+    for x in a.iteritems():
+        print(x)
+    print("--")
+    print("b", b)
+    for x in b.iteritems(readonly=True):
+        print(x)
+    print()