Fix the issue when persistent DVS is used to run pytest which has num…

…ber of front-panel ports < 32 (sonic-net#1373)

* Fix the issue where persistent DVS is used to run pytest
and ports are created dynamically (ref pr:
sonic-net#4499). There were two
issues:

a) since number of dynamic front port can be < 32 test case fails
   as it expect always 32. Make sure to udpate persitent DVS to always have
   32 ports/server link as part of test run and save the current config
   db

b) after test is done persistent DVS need to be moved to original state.
   Make dure to remove extra port/server link and restore back config db

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

* Review Comments fix

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

* Added option for force persitent dvs if port < 32
Updated Readme

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

* Fix LGTM

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

* Fix LGTM and compile error

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

* Update tests/conftest.py

Co-authored-by: Danny Allen <daall@microsoft.com>

Co-authored-by: Danny Allen <daall@microsoft.com>

tests/README.md

@@ -71,6 +71,12 @@ For those developing new features for SWSS or the DVS framework, you might find
     ```
     sudo pytest --dvsname=vs
     ```
+    By default if number of ports in persistent DVS < 32 (needed by testbed) then test will be aborted. To overcome that --forcedvs option can be used.
+
+    ```
+    sudo pytest --dvsname=vs --forcedvs
+    ```
+
 
 5. Additionally, if you need to simulate a specific hardware platform (e.g. Broadcom or Mellanox), you can add this environment variable when starting the DVS container:
 

tests/conftest.py

@@ -41,6 +41,8 @@ def ensure_system(cmd):
 def pytest_addoption(parser):
     parser.addoption("--dvsname", action="store", default=None,
                       help="dvs name")
+    parser.addoption("--forcedvs", action="store_true", default=False,
+                      help="force persistent dvs when ports < 32")
     parser.addoption("--keeptb", action="store_true", default=False,
                       help="keep testbed after test")
     parser.addoption("--imgname", action="store", default="docker-sonic-vs",
@@ -191,7 +193,8 @@ def __init__(
             keeptb=False,
             fakeplatform=None,
             log_path=None,
-            max_cpu=2
+            max_cpu=2,
+            forcedvs=None,
     ):
         self.basicd = ['redis-server',
                        'rsyslogd']
@@ -220,6 +223,7 @@ def __init__(
             self.cleanup = False
         else:
             self.cleanup = True
+        self.persistent = False
         if name != None:
             # get virtual switch container
             for ctn in self.client.containers.list():
@@ -230,10 +234,20 @@ def __init__(
                     else:
                         (status, output) = subprocess.getstatusoutput("docker inspect --format '{{.HostConfig.NetworkMode}}' %s" % name)
                     ctn_sw_id = output.split(':')[1]
+                    # Persistent DVS is available.
                     self.cleanup = False
+                    self.persistent = True
             if self.ctn == None:
                 raise NameError("cannot find container %s" % name)
 
+            self.num_net_interfaces = self.net_interface_count()
+
+            if self.num_net_interfaces > NUM_PORTS:
+                raise ValueError("persistent dvs is not valid for testbed with ports > %d" % NUM_PORTS)
+
+            if self.num_net_interfaces < NUM_PORTS and not forcedvs:
+                raise ValueError("persistent dvs does not have %d ports needed by testbed" % NUM_PORTS)
+
             # get base container
             for ctn in self.client.containers.list():
                 if ctn.id == ctn_sw_id or ctn.name == ctn_sw_id:
@@ -254,6 +268,10 @@ def __init__(
             self.mount = "/var/run/redis-vs/{}".format(ctn_sw_name)
 
             self.net_cleanup()
+            # As part of https://github.com/Azure/sonic-buildimage/pull/4499
+            # VS support dynamically create Front-panel ports so save the orginal
+            # config db for persistent DVS
+            self.runcmd("mv /etc/sonic/config_db.json /etc/sonic/config_db.json.orig")
             self.ctn_restart()
         else:
             self.ctn_sw = self.client.containers.run('debian:jessie', privileged=True, detach=True,
@@ -301,7 +319,13 @@ def __init__(
     def destroy(self):
         if self.appldb:
             del self.appldb
-        if self.cleanup:
+        # In case persistent dvs was used removed all the extra server link
+        # that were created
+        if self.persistent:
+            for s in self.servers:
+                s.destroy()
+        # persistent and clean-up flag are mutually exclusive
+        elif self.cleanup:
             self.ctn.remove(force=True)
             self.ctn_sw.remove(force=True)
             os.system("rm -rf {}".format(self.mount))
@@ -418,6 +442,21 @@ def net_cleanup(self):
                     print("remove extra link {}".format(pname))
         return
 
+    def net_interface_count(self):
+        """get the interface count in persistent DVS Container
+           if not found or some error then return 0 as default"""
+
+        res = self.ctn.exec_run(['sh', '-c', 'ip link show | grep -oE eth[0-9]+ | grep -vc eth0'])
+        if not res.exit_code:
+            try:
+                out = res.output.decode('utf-8')
+            except AttributeError:
+                return 0
+            return int(out.rstrip('\n'))
+        else:
+            return 0
+
+
     def ctn_restart(self):
         self.ctn.restart()
 
@@ -906,7 +945,7 @@ def remove_neighbor(self, interface, ip):
     def add_route(self, prefix, nexthop):
         self.runcmd("ip route add " + prefix + " via " + nexthop)
         time.sleep(1)
-
+    
     def remove_route(self, prefix):
         self.runcmd("ip route del " + prefix)
         time.sleep(1)
@@ -1008,18 +1047,23 @@ def get_state_db(self):
 @pytest.yield_fixture(scope="module")
 def dvs(request) -> DockerVirtualSwitch:
     name = request.config.getoption("--dvsname")
+    forcedvs = request.config.getoption("--forcedvs")
     keeptb = request.config.getoption("--keeptb")
     imgname = request.config.getoption("--imgname")
     max_cpu = request.config.getoption("--max_cpu")
     fakeplatform = getattr(request.module, "DVS_FAKE_PLATFORM", None)
     log_path = name if name else request.module.__name__
 
-    dvs = DockerVirtualSwitch(name, imgname, keeptb, fakeplatform, log_path, max_cpu)
+    dvs = DockerVirtualSwitch(name, imgname, keeptb, fakeplatform, log_path, max_cpu, forcedvs)
 
     yield dvs
 
     dvs.get_logs()
     dvs.destroy()
+    # restore original config db
+    if dvs.persistent:
+        dvs.runcmd("mv /etc/sonic/config_db.json.orig /etc/sonic/config_db.json")
+        dvs.ctn_restart()
 
 @pytest.yield_fixture
 def testlog(request, dvs):