TAPSET::SNMP(3stap)													       TAPSET::SNMP(3stap)

NAME

       tapset::snmp - Systemtap simple network management protocol probe points.

DESCRIPTION

       This  family  of  probe	points enhances the Linux system's implementation of the Simple Network Management Protocol (SNMP) by allowing the
       user to collect per-socket statistics. SNMP data is collected in the Linux kernel by counting various events occurring  in  the	networking
       subsystem.  Linux provides one counter for each type of event, thus providing a system-wide collection of network statistics. These statis-
       tics can be viewed with the command: netstat -s.

       The probe points defined in the SNMP group of tapsets allow users to aberrate each SNMP counter into groups of counters. For  example,  the
       user may count SNMP events for a single network socket or for a group of sockets.

       Severals  SNMP tapsets have been created. Each tapset represents a single layer of the network stack and defines a group of counters called
       management information blocks or MIBs. Currently tapsets are provided that support MIBS for IP, TCP layers and the enhanced linux MIB.  See
       the file /usr/include/linux/snmp.h for a list of MIBS supported by linux.

PROBE HANDLERS, COUNTERS AND CALLBACKS
       Each  probe  represents	a single SNMP statistic. The probe's handler is called each time the system performs an operation that would alter
       the associated statistic. Each probe also defines an indexed set of counters used to record probe hits. The probe handler calls a user sup-
       plied  callback functions to determine which counter to alter. The user's callback should return a key value that will be used to index the
       counter. For example a callback could return a unique value for each socket. This would results in a separate counter being used  for  each
       socket.

       Each  tapset is now described. Examples of probe names and counter names are given. See the  tapset itself for a complete list of supported
       probes. Users of the tapset must provide a callback function matching the name and prototype as shown.

       IP MIB Tapset:

       Example probe name: ipmib.InReceives

       Example counter name: InReceives

       Callback prototype:

       ipmib_filter_key:long (skb:long, op:long, SourceIsLocal:long)

       This user supplied function should compute and return a value used to index the statistical counter. The skb is a  pointer  to  the  struct
       sk_buff being processed at the time. The local ip-address and port number will be located in either the source or destination fields of the
       network packet.	SourceIsLocal will be true if the local address is in the source field. The probe handler will add the value of op to  the
       counter. To skip counting the event return a value of zero.

       TCP MIB tapset:

       Example probe name: tcpmib.InSegs

       Example counter name: InSegs

       Callback prototype:

       tcpmib_filter_key:long (sk:long, op:long)

       This user supplied function should compute and return a value used to index the statistical counter. The sk is a pointer to the struct sock
       being processed at the time. The probe handler will add the value of op to the counter. To skip counting the event return a value of zero.

       LINUX MIB tapset:

       linuxmib.stp

       Example probe name: linuxmib.DelayedACKs

       Example counter name: DelayedACKs

       Callback prototype:

       linuxmib_filter_key:long (sk:long, op:long)

       This user supplied function should compute and return a value used to index the statistical counter. The sk is a pointer to the struct sock
       being processed at the time. The probe handler will add the value of op to the counter. To skip counting the event return a value of zero.

EXAMPLE

       This example script counts the number of TCP retransmits and records them per-remote address. It displays the counts when terminated.

	      /* Enable the statistic we want to record. */
	      probe tcpmib.RetransSegs {}

	      /*
	       * Find the remote address and return
	       * it as an index to the counter array.
	       */
	      function tcpmib_filter_key: long ( sk:long, op:long ){
		   if ( !sk ) return 0;
		   raddr = sk_get_daddr(sk);
		   return raddr
	      }

	      /* Print the results. */
	      probe end {
		   foreach (addr in  RetransSegs )
			printf ("%s  %d 
 ",ip_ntop(htonl(addr)), lport)
	      }

FILES

       /usr/share/doc/systemtap*/examples/tcpipstat.stp

SEE ALSO

       stap(1), stapprobes(3stap), stapfuncs(3stap)

IBM
															       TAPSET::SNMP(3stap)