ovs python: ovs.stream.open_block() returns success even if the remote is unreachable

The python function ovs.socket_util.check_connection_completion() uses select()
(provided by python) to monitor the socket file descriptor. The select()
returns 1 when the file descriptor becomes ready. For error cases like -
111 (Connection refused) and 113 (No route to host) (POLLERR), ovs.poller._SelectSelect.poll()
expects the exceptfds list to be set by select(). But that is not the case.
As per the select() man page, writefds list will be set for POLLERR.
Please see "Correspondence between select() and poll() notifications" section of select(2)
man page.

Because of this behavior, ovs.socket_util.check_connection_completion() returns success
even if the remote is unreachable or not listening on the port.

This patch fixes this issue by using poll() to check the connection status similar to
the C implementation of check_connection_completion().

A new function 'get_system_poll() is added in ovs/poller.py which returns the
select.poll() object. If select.poll is monkey patched by eventlet/gevent, it
gets the original select.poll() and returns it.

The test cases added in this patch fails without the fix.

Suggested-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Mark Michelson <mmichels@redhat.com>

python/ovs/poller.py

@@ -31,14 +31,22 @@ except ImportError:
     SSL = None
 
 try:
-    import eventlet.patcher
+    from eventlet import patcher as eventlet_patcher
 
     def _using_eventlet_green_select():
-        return eventlet.patcher.is_monkey_patched(select)
+        return eventlet_patcher.is_monkey_patched(select)
 except:
+    eventlet_patcher = None
+
     def _using_eventlet_green_select():
         return False
 
+try:
+    from gevent import monkey as gevent_monkey
+except:
+    gevent_monkey = None
+
+
 vlog = ovs.vlog.Vlog("poller")
 
 POLLIN = 0x001
@@ -257,3 +265,26 @@ class Poller(object):
     def __reset(self):
         self.poll = SelectPoll()
         self.timeout = -1
+
+
+def get_system_poll():
+    """Returns the original select.poll() object. If select.poll is
+    monkey patched by eventlet or gevent library, it gets the original
+    select.poll and returns an object of it using the
+    eventlet.patcher.original/gevent.monkey.get_original functions.
+
+    As a last resort, if there is any exception it returns the
+    SelectPoll() object.
+    """
+    try:
+        if _using_eventlet_green_select():
+            _system_poll = eventlet_patcher.original("select").poll
+        elif gevent_monkey and gevent_monkey.is_object_patched(
+                'select', 'poll'):
+            _system_poll = gevent_monkey.get_original('select', 'poll')
+        else:
+            _system_poll = select.poll
+    except:
+        _system_poll = SelectPoll
+
+    return _system_poll()

python/ovs/socket_util.py

@@ -162,8 +162,8 @@ def make_unix_socket(style, nonblock, bind_path, connect_path, short=False):
 
 
 def check_connection_completion(sock):
-    p = ovs.poller.SelectPoll()
     if sys.platform == "win32":
+        p = ovs.poller.SelectPoll()
         event = winutils.get_new_event(None, False, True, None)
         # Receive notification of readiness for writing, of completed
         # connection or multipoint join operation, and of socket closure.
@@ -173,6 +173,7 @@ def check_connection_completion(sock):
                                  win32file.FD_CLOSE)
         p.register(event, ovs.poller.POLLOUT)
     else:
+        p = ovs.poller.get_system_poll()
         p.register(sock, ovs.poller.POLLOUT)
     pfds = p.poll(0)
     if len(pfds) == 1:
@@ -180,7 +181,7 @@ def check_connection_completion(sock):
         if revents & ovs.poller.POLLERR:
             try:
                 # The following should raise an exception.
-                socket.send("\0", socket.MSG_DONTWAIT)
+                sock.send("\0".encode(), socket.MSG_DONTWAIT)
 
                 # (Here's where we end up if it didn't.)
                 # XXX rate-limit

python/ovs/stream.py

@@ -191,8 +191,15 @@ class Stream(object):
         if error:
             return error, None
         else:
-            status = ovs.socket_util.check_connection_completion(sock)
-            return 0, cls(sock, name, status)
+            err = ovs.socket_util.check_connection_completion(sock)
+            if err == errno.EAGAIN or err == errno.EINPROGRESS:
+                status = errno.EAGAIN
+                err = 0
+            elif err == 0:
+                status = 0
+            else:
+                status = err
+            return err, cls(sock, name, status)
 
     @staticmethod
     def _open(suffix, dscp):