diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -451,6 +451,13 @@
             self._lenbuf += len(data)
             self._buffer.append(data)
 
+        # If this is our special proxied file object class, log this I/O,
+        # since os.read() bypasses the proxy.
+        if isinstance(self._input, fileobjectproxy):
+            fn = getattr(self._input._observer, r'osread', None)
+            if fn:
+                self._input._observer.osread(data, _chunksize)
+
 def mmapread(fp):
     try:
         fd = getattr(fp, 'fileno', lambda: fp)()
@@ -503,6 +510,8 @@
 
     def __getattribute__(self, name):
         ours = {
+            r'_observer',
+
             # IOBase
             r'close',
             # closed if a property
@@ -679,6 +688,10 @@
         self.fh.write('%s> readline() -> %d' % (self.name, len(res)))
         self._writedata(res)
 
+    def osread(self, res, size):
+        self.fh.write('%s> osread(%d) -> %d' % (self.name, size, len(res)))
+        self._writedata(res)
+
     def write(self, res, data):
         self.fh.write('%s> write(%d) -> %r' % (self.name, len(data), res))
         self._writedata(data)