Common functions for show CLI support on multi ASIC (sonic-net#999)

Common changes will be used to support SONiC CLIs for multi ASIC
- New MultiAsic class  to support not displaying of internal object 
- Common CLI options which needed for multi ASIC platforms
- a new decorator to execute a function on all namespaces

Signed-off-by: Arvindsrinivasan Lakshmi Narasimhan <arlakshm@microsoft.com>

utilities_common/constants.py

@@ -0,0 +1,9 @@
+#All the constant used in sonic-utilities
+
+DEFAULT_NAMESPACE = ''
+DISPLAY_ALL = 'all'
+DISPLAY_EXTERNAL = 'frontend'
+BGP_NEIGH_OBJ = 'BGP_NEIGH'
+PORT_CHANNEL_OBJ = 'PORT_CHANNEL'
+PORT_OBJ = 'PORT'
+

utilities_common/multi_asic.py

@@ -0,0 +1,138 @@
+import argparse
+import functools
+
+import click
+from sonic_py_common import multi_asic
+from utilities_common import constants
+
+
+class MultiAsic(object):
+
+    def __init__(self, display_option=constants.DISPLAY_ALL,
+                 namespace_option=None):
+        self.namespace_option = namespace_option
+        self.display_option = display_option
+        self.current_namespace = None
+        self.is_multi_asic = multi_asic.is_multi_asic()
+
+    def is_object_internal(self, object_type, cli_object):
+        '''
+        The function checks if a CLI object is internal and returns true or false.
+        Internal objects are port or portchannel which are connected to other 
+        ports or portchannels within a multi ASIC device.
+
+        For single asic, this function is not applicable
+        '''
+        if object_type == constants.PORT_OBJ:
+            return multi_asic.is_port_internal(cli_object)
+        elif object_type == constants.PORT_CHANNEL_OBJ:
+            return multi_asic.is_port_channel_internal(cli_object)
+        elif object_type == constants.BGP_NEIGH_OBJ:
+            return multi_asic.is_bgp_session_internal(cli_object)
+
+    def skip_display(self, object_type, cli_object):
+        '''
+        The function determines if the passed cli_object has to be displayed or not.
+        returns true if the display_option is external and  the cli object is internal.
+        returns false, if the cli option is all or if it the platform is single ASIC.
+
+        '''
+        if not self.is_multi_asic:
+            return False
+        if self.display_option == constants.DISPLAY_ALL:
+            return False
+        return self.is_object_internal(object_type, cli_object)
+
+    def get_ns_list_based_on_options(self):
+        ns_list = []
+        if not self.is_multi_asic:
+            return [constants.DEFAULT_NAMESPACE]
+        else:
+            namespaces = multi_asic.get_all_namespaces()
+            if self.namespace_option is None:
+                if self.display_option == constants.DISPLAY_ALL:
+                    ns_list = namespaces['front_ns'] + namespaces['back_ns']
+                else:
+                    ns_list = namespaces['front_ns']
+            else:
+                if self.namespace_option not in namespaces['front_ns'] and \
+                        self.namespace_option not in namespaces['back_ns']:
+                    raise ValueError(
+                        'Unknown Namespace {}'.format(self.namespace_option))
+                ns_list = [self.namespace_option]
+        return ns_list
+
+
+def multi_asic_ns_choices():
+    if not multi_asic.is_multi_asic():
+        return [constants.DEFAULT_NAMESPACE]
+    choices = multi_asic.get_namespace_list()
+    return choices
+
+
+def multi_asic_display_choices():
+    if not multi_asic.is_multi_asic():
+        return [constants.DISPLAY_ALL]
+    else:
+        return [constants.DISPLAY_ALL, constants.DISPLAY_EXTERNAL]
+
+
+def multi_asic_display_default_option():
+    if not multi_asic.is_multi_asic():
+        return constants.DISPLAY_ALL
+    else:
+        return constants.DISPLAY_EXTERNAL
+
+
+_multi_asic_click_options = [
+    click.option('--display',
+                 '-d', 'display',
+                 default=multi_asic_display_default_option(),
+                 show_default=True,
+                 type=click.Choice(multi_asic_display_choices()),
+                 help='Show internal interfaces'),
+    click.option('--namespace',
+                 '-n', 'namespace',
+                 default=None,
+                 type=click.Choice(multi_asic_ns_choices()),
+                 show_default=True,
+                 help='Namespace name or all'),
+]
+
+
+def multi_asic_click_options(func):
+    for option in reversed(_multi_asic_click_options):
+        func = option(func)
+    return func
+
+
+def run_on_multi_asic(func):
+    '''
+    This decorator is used on the CLI functions which needs to be
+    run on all the namespaces in the multi ASIC platform
+    The decorator loops through all the required namespaces,
+    for every iteration, it connects to all the DBs and provides an handle
+    to the wrapped function.
+
+    '''
+    @functools.wraps(func)
+    def wrapped_run_on_all_asics(self, *args, **kwargs):
+        ns_list = self.multi_asic.get_ns_list_based_on_options()
+        for ns in ns_list:
+            self.multi_asic.current_namespace = ns
+            self.db = multi_asic.connect_to_all_dbs_for_ns(ns)
+            self.config_db = multi_asic.connect_config_db_for_ns(ns)
+            func(self,  *args, **kwargs)
+    return wrapped_run_on_all_asics
+
+
+def multi_asic_args(parser=None):
+    if parser is None:
+        parser = argparse.ArgumentParser(
+            formatter_class=argparse.RawTextHelpFormatter)
+
+    parser.add_argument('-d', '--display', default=constants.DISPLAY_EXTERNAL,
+                        help='Display all interfaces or only external interfaces')
+    parser.add_argument('-n', '--namespace', default=None,
+                        help='Display interfaces for specific namespace')
+    return parser