TAPSET::SNMP(3stap)TAPSET::SNMP(3stap)NAMEtapset::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 subsys‐
tem. Linux provides one counter for each type of event, thus providing
a system-wide collection of network statistics. These statistics 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 sin‐
gle 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 coun‐
ters used to record probe hits. The probe handler calls a user supplied
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 num‐
ber 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 ALSOstap(1), stapprobes(3stap), stapfuncs(3stap)IBMTAPSET::SNMP(3stap)
