diff --git a/meta/classes/externalsrc.bbclass b/meta/classes/externalsrc.bbclass
new file mode 100644
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+++ b/meta/classes/externalsrc.bbclass
@@ -0,0 +1,92 @@
+# Copyright (C) 2012 Linux Foundation
+# Author: Richard Purdie
+# Some code and influence taken from srctree.bbclass:
+# Copyright (C) 2009 Chris Larson <clarson@kergoth.com>
+# Released under the MIT license (see COPYING.MIT for the terms)
+#
+# externalsrc.bbclass enables use of an existing source tree, usually external to 
+# the build system to build a piece of software rather than the usual fetch/unpack/patch
+# process.
+#
+# To use, add externalsrc to the global inherit and set EXTERNALSRC to point at the
+# directory you want to use containing the sources e.g. from local.conf for a recipe
+# called "myrecipe" you would do:
+#
+# INHERIT += "externalsrc"
+# EXTERNALSRC_pn-myrecipe = "/path/to/my/source/tree"
+#
+# In order to make this class work for both target and native versions (or with
+# multilibs/cross or other BBCLASSEXTEND variants), B is set to point to a separate
+# directory under the work directory (split source and build directories). This is
+# the default, but the build directory can be set to the source directory if
+# circumstances dictate by setting EXTERNALSRC_BUILD to the same value, e.g.:
+#
+# EXTERNALSRC_BUILD_pn-myrecipe = "/path/to/my/source/tree"
+#
+
+SRCTREECOVEREDTASKS ?= "do_patch do_unpack do_fetch"
+
+python () {
+    externalsrc = d.getVar('EXTERNALSRC', True)
+    if externalsrc:
+        d.setVar('S', externalsrc)
+        externalsrcbuild = d.getVar('EXTERNALSRC_BUILD', True)
+        if externalsrcbuild:
+            d.setVar('B', externalsrcbuild)
+        else:
+            d.setVar('B', '${WORKDIR}/${BPN}-${PV}/')
+
+        local_srcuri = []
+        fetch = bb.fetch2.Fetch((d.getVar('SRC_URI', True) or '').split(), d)
+        for url in fetch.urls:
+            url_data = fetch.ud[url]
+            parm = url_data.parm
+            if (url_data.type == 'file' or
+                    'type' in parm and parm['type'] == 'kmeta'):
+                local_srcuri.append(url)
+
+        d.setVar('SRC_URI', ' '.join(local_srcuri))
+
+        if '{SRCPV}' in d.getVar('PV', False):
+            # Dummy value because the default function can't be called with blank SRC_URI
+            d.setVar('SRCPV', '999')
+
+        tasks = filter(lambda k: d.getVarFlag(k, "task"), d.keys())
+
+        for task in tasks:
+            if task.endswith("_setscene"):
+                # sstate is never going to work for external source trees, disable it
+                bb.build.deltask(task, d)
+            else:
+                # Since configure will likely touch ${S}, ensure only we lock so one task has access at a time
+                d.appendVarFlag(task, "lockfiles", " ${S}/singletask.lock")
+
+            # We do not want our source to be wiped out, ever (kernel.bbclass does this for do_clean)
+            cleandirs = (d.getVarFlag(task, 'cleandirs', False) or '').split()
+            setvalue = False
+            for cleandir in cleandirs[:]:
+                if d.expand(cleandir) == externalsrc:
+                    cleandirs.remove(cleandir)
+                    setvalue = True
+            if setvalue:
+                d.setVarFlag(task, 'cleandirs', ' '.join(cleandirs))
+
+        fetch_tasks = ['do_fetch', 'do_unpack']
+        # If we deltask do_patch, there's no dependency to ensure do_unpack gets run, so add one
+        d.appendVarFlag('do_configure', 'deps', ['do_unpack'])
+
+        for task in d.getVar("SRCTREECOVEREDTASKS", True).split():
+            if local_srcuri and task in fetch_tasks:
+                continue
+            bb.build.deltask(task, d)
+
+        d.prependVarFlag('do_compile', 'prefuncs', "externalsrc_compile_prefunc ")
+
+        # Ensure compilation happens every time
+        d.setVarFlag('do_compile', 'nostamp', '1')
+}
+
+python externalsrc_compile_prefunc() {
+    # Make it obvious that this is happening, since forgetting about it could lead to much confusion
+    bb.warn('Compiling %s from external source %s' % (d.getVar('PN', True), d.getVar('EXTERNALSRC', True)))
+}