diff --git a/hgext/blackbox.py b/hgext/blackbox.py
new file mode 100644
--- /dev/null
+++ b/hgext/blackbox.py
@@ -0,0 +1,77 @@
+# worker.py - master-slave parallelism support
+#
+# Copyright 2013 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+"""log repository events to a blackbox for debugging
+
+Logs event information to .hg/blackbox.log to help debug and diagnose problems.
+The events that get logged can be configured via the blackbox.track config key.
+Examples:
+
+  [blackbox]
+  track = *
+
+  [blackbox]
+  track = command, commandfinish, commandexception, exthook, pythonhook
+
+  [blackbox]
+  track = incoming
+
+"""
+
+from mercurial import util, cmdutil
+from mercurial.i18n import _
+import os, getpass, re, string
+
+cmdtable = {}
+command = cmdutil.command(cmdtable)
+testedwith = 'internal'
+lastblackbox = None
+
+def wrapui(ui):
+    class blackboxui(ui.__class__):
+        @util.propertycache
+        def track(self):
+            return ui.configlist('blackbox', 'track', ['*'])
+
+        def log(self, event, *msg, **opts):
+            global lastblackbox
+            super(blackboxui, self).log(event, *msg, **opts)
+
+            if not '*' in self.track and not event in self.track:
+                return
+
+            if util.safehasattr(self, '_blackbox'):
+                blackbox = self._blackbox
+            else:
+                # certain ui instances exist outside the context of
+                # a repo, so just default to the last blackbox that
+                # was seen.
+                blackbox = lastblackbox
+
+            if blackbox:
+                date = util.datestr(None, '%Y/%m/%d %H:%M:%S')
+                user = getpass.getuser()
+                formattedmsg = msg[0] % msg[1:]
+                blackbox.write('%s %s> %s' % (date, user, formattedmsg))
+                lastblackbox = blackbox
+
+        def setrepo(self, repo):
+            self._blackbox = repo.opener('blackbox.log', 'a')
+
+    ui.__class__ = blackboxui
+
+def uisetup(ui):
+    wrapui(ui)
+
+def reposetup(ui, repo):
+    # During 'hg pull' a httppeer repo is created to represent the remote repo.
+    # It doesn't have a .hg directory to put a blackbox in, so we don't do
+    # the blackbox setup for it.
+    if not repo.local():
+        return
+
+    ui.setrepo(repo)
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -739,7 +739,7 @@ class ui(object):
         else:
             self.debug('%s:%s %s%s\n' % (topic, item, pos, unit))
 
-    def log(self, service, message):
+    def log(self, service, *msg, **opts):
         '''hook for logging facility extensions
 
         service should be a readily-identifiable subsystem, which will