T5702: SNMP add interface-mib max-interfaces-number and prefix

- Allow to configure only required interface prefixes

  set service snmp mib interface 'eth'
  set service snmp mib interface 'bond'

 include_ifmib_iface_prefix eth bond

Sets the interface name prefixes to include in the IF-MIB data collection.
For servers with a large number of interfaces (ppp, dummy, bridge, etc)
the IF-MIB processing will take a large chunk of CPU for ioctl calls.
A set of space separated interface name prefixes will reduce the CPU
load for IF-MIB processing. For example, configuring
"include_ifmib_iface_prefix eth dummy lo" will include only interfaces
with these prefixes and ignore all others for IF-MIB processing.

- Allow to configure maximum interface number

  set service snmp mib interface-max '100'

  ifmib_max_num_ifaces NUM

Sets the maximum number of interfaces included in IF-MIB data collection.
For servers with a large number of interfaces (ppp, dummy, bridge, etc)
the IF-MIB processing will take a large chunk of CPU for ioctl calls
(on Linux). Setting a reasonable maximum for the CPU used will
reduce the CPU load for IF-MIB processing.  For example, configuring
"ifmib_max_num_ifaces 500" will include only the first 500 interfaces
based on ifindex and ignore all others for IF-MIB processing.

data/templates/snmp/etc.snmpd.conf.j2

@@ -56,6 +56,16 @@ SysDescr {{ description }}
 {% endif %}
 agentaddress unix:/run/snmpd.socket{{ ',' ~ options | join(',') if options is vyos_defined }}
 
+{% if mib is vyos_defined %}
+# Interface MIB limits
+{%     if mib.interface_max is vyos_defined %}
+ifmib_max_num_ifaces {{ mib.interface_max }}
+{%     endif %}
+{%     if mib.interface is vyos_defined %}
+include_ifmib_iface_prefix {{ mib.interface | join(' ') }}
+{%     endif %}
+{% endif %}
+
 # SNMP communities
 {% if community is vyos_defined %}
 {%     for comm, comm_config in community.items() %}

interface-definitions/snmp.xml.in

@@ -79,6 +79,39 @@
             </properties>
           </leafNode>
           #include <include/generic-description.xml.i>
+          <node name="mib">
+            <properties>
+              <help>Management information base (MIB)</help>
+            </properties>
+            <children>
+              <leafNode name="interface-max">
+                <properties>
+                  <help>Sets the maximum number of interfaces included in IF-MIB data collection</help>
+                  <valueHelp>
+                    <format>u32:1-4294967295</format>
+                    <description>Sets the maximum number of interfaces included in IF-MIB data collection</description>
+                  </valueHelp>
+                  <constraint>
+                    <validator name="numeric" argument="--range 1-4294967295"/>
+                  </constraint>
+                </properties>
+              </leafNode>
+              <leafNode name="interface">
+                <properties>
+                  <help>Sets the interface name prefix to include in the IF-MIB data collection</help>
+                  <valueHelp>
+                    <format>txt</format>
+                    <description>Sets the interface name prefix to include in the IF-MIB data collection</description>
+                  </valueHelp>
+                  <constraint>
+                    <regex>(\!?)(bond|br|dum|en|ersp|eth|gnv|ifb|lan|l2tp|l2tpeth|macsec|peth|ppp|pppoe|pptp|sstp|tun|veth|vti|vtun|vxlan|wg|wlan|wwan)([0-9]?)(\*?)(.+)?|(\!?)lo</regex>
+                    <validator name="vrf-name"/>
+                  </constraint>
+                  <multi/>
+                </properties>
+              </leafNode>
+            </children>
+          </node>
           <tagNode name="listen-address">
             <properties>
               <help>IP address to listen for incoming SNMP requests</help>