[Plugin,networking] Move namespace filtering to get_network_namespaces()

Copy the logic over from the networking plugin to `filter_namespaces()`,
which is generic, taking any list of namespaces; and then wrap it in
`get_network_namespaces()` for the particular network namespace type.

Now other plugins may be able to filter namespaces as well, and
not only network namespaces, but other types that may be added
(which can get convenience wrappers `get_X_namespaces()` then.)

In order to make the review simpler, the changes for the networking
plugin are intentionally small (keep the optional `if self.g_n_n():`
and only filter in `out_ns` which is used in `ethtool_namespaces`.)
The next patch addresses that, with the larger indentation changes.

Testing with the networking plugins' options to filter namespaces
by a regex pattern, and limit by the number:

```
    $ ip netns
    ns3
    ns2
    ns1
```

Option `networking.namespace_pattern` (only namespaces with trailing 2):
```
    $ sudo ./bin/sos report -o networking \
        -k networking.namespace_pattern='.*2' --batch

    $ find sosreport-*/sos_commands/networking \
        | cut -d/ -f2- | grep ip_netns_exec
    sos_commands/networking/ip_netns_exec_ns2_iptables-save
    sos_commands/networking/ip_netns_exec_ns2_ip_-s_-s_neigh_show
    sos_commands/networking/ip_netns_exec_ns2_ip_address_show
    sos_commands/networking/ip_netns_exec_ns2_ip_route_show_table_all
    sos_commands/networking/ip_netns_exec_ns2_ethtool_-i_lo
    sos_commands/networking/ip_netns_exec_ns2_ethtool_-k_lo
    sos_commands/networking/ip_netns_exec_ns2_ethtool_-S_lo
    sos_commands/networking/ip_netns_exec_ns2_ethtool_lo
    sos_commands/networking/ip_netns_exec_ns2_ip6tables-save
    sos_commands/networking/ip_netns_exec_ns2_netstat_-W_-agn
    sos_commands/networking/ip_netns_exec_ns2_netstat_-W_-neopa
    sos_commands/networking/ip_netns_exec_ns2_ip_rule_list
    sos_commands/networking/ip_netns_exec_ns2_netstat_-s
```

Option `networking.namespaces` (only one namespace):
```
    $ sudo ./bin/sos report -o networking \
        -k networking.namespaces=1 --batch

    $ grep 'Limiting namespace iteration' sosreport-*/sos_logs/sos.log
    2020-11-18 22:48:00,263 WARNING: [plugin:networking] \
    Limiting namespace iteration to first 1 namespaces found

    $ find sosreport-*/sos_commands/networking \
        | cut -d/ -f2- | grep ip_netns_exec
    sos_commands/networking/ip_netns_exec_ns3_ethtool_-i_lo
    sos_commands/networking/ip_netns_exec_ns3_ip_rule_list
    sos_commands/networking/ip_netns_exec_ns3_ip_route_show_table_all
    sos_commands/networking/ip_netns_exec_ns3_netstat_-W_-neopa
    sos_commands/networking/ip_netns_exec_ns3_netstat_-s
    sos_commands/networking/ip_netns_exec_ns3_ethtool_-k_lo
    sos_commands/networking/ip_netns_exec_ns3_netstat_-W_-agn
    sos_commands/networking/ip_netns_exec_ns3_iptables-save
    sos_commands/networking/ip_netns_exec_ns3_ip_address_show
    sos_commands/networking/ip_netns_exec_ns3_ip_-s_-s_neigh_show
    sos_commands/networking/ip_netns_exec_ns3_ip6tables-save
    sos_commands/networking/ip_netns_exec_ns3_ethtool_-S_lo
    sos_commands/networking/ip_netns_exec_ns3_ethtool_lo
```

Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Signed-off-by: Jake Hunsaker <jhunsake@redhat.com>

2 files changed, 37 insertions, 27 deletions

diff --git a/sos/report/plugins/__init__.py b/sos/report/plugins/__init__.py
index b60113ad..deb46c93 100644
--- a/sos/report/plugins/__init__.py
+++ b/sos/report/plugins/__init__.py
@@ -2680,8 +2680,40 @@ class Plugin(object):
                 continue
         return pids
 
-    def get_network_namespaces(self):
-        return self.commons['namespaces']['network']
+    def get_network_namespaces(self, ns_pattern=None, ns_max=0):
+        return self.filter_namespaces(self.commons['namespaces']['network'],
+                                      ns_pattern, ns_max)
+
+    def filter_namespaces(self, ns_list, ns_pattern=None, ns_max=0):
+        """Filter a list of namespaces by regex pattern or max number of
+        namespaces (options originally present in the networking plugin.)
+        """
+        out_ns = []
+
+        # Regex initialization outside of for loop
+        if ns_pattern:
+            pattern = (
+                '(?:%s$)' % '$|'.join(ns_pattern.split()).replace('*', '.*')
+                )
+        for ns in ns_list:
+            # if ns_pattern defined, append only namespaces
+            # matching with pattern
+            if ns_pattern:
+                if bool(re.match(pattern, ns)):
+                    out_ns.append(ns)
+
+            # if ns_max is defined and ns_pattern is not defined
+            # remove from out_ns namespaces with higher index than defined
+            elif ns_max != 0:
+                out_ns.append(ns)
+                if len(out_ns) == ns_max:
+                    self._log_warn("Limiting namespace iteration "
+                                   "to first %s namespaces found"
+                                   % ns_max)
+                    break
+            else:
+                out_ns.append(ns)
+        return out_ns
 
 
 class RedHatPlugin(object):
diff --git a/sos/report/plugins/networking.py b/sos/report/plugins/networking.py
index 7718901b..a919fa17 100644
--- a/sos/report/plugins/networking.py
+++ b/sos/report/plugins/networking.py
@@ -9,7 +9,6 @@
 from sos.report.plugins import (Plugin, RedHatPlugin, UbuntuPlugin,
                                 DebianPlugin, SoSPredicate)
 from os import listdir
-from re import match
 
 
 class Networking(Plugin):
@@ -233,30 +232,9 @@ class Networking(Plugin):
         self.add_cmd_output("ip netns")
         cmd_prefix = "ip netns exec "
         if self.get_network_namespaces():
-            out_ns = []
-            # Regex initialization outside of for loop
-            if self.get_option("namespace_pattern"):
-                pattern = '(?:%s$)' % '$|'.join(
-                        self.get_option("namespace_pattern").split()
-                        ).replace('*', '.*')
-            for ns in self.get_network_namespaces():
-                # if namespace_pattern defined, append only namespaces
-                # matching with pattern
-                if self.get_option("namespace_pattern"):
-                    if bool(match(pattern, ns)):
-                        out_ns.append(ns)
-
-                # if namespaces is defined and namespace_pattern is not defined
-                # remove from out_ns namespaces with higher index than defined
-                elif self.get_option("namespaces") != 0:
-                    out_ns.append(ns)
-                    if len(out_ns) == self.get_option("namespaces"):
-                        self._log_warn("Limiting namespace iteration " +
-                                       "to first %s namespaces found"
-                                       % self.get_option("namespaces"))
-                        break
-                else:
-                    out_ns.append(ns)
+            out_ns = self.get_network_namespaces(
+                        self.get_option("namespace_pattern"),
+                        self.get_option("namespaces"))
 
             for namespace in out_ns:
                 ns_cmd_prefix = cmd_prefix + namespace + " "