Guys,
I am setting up snmpd on a ARM device with network drivers that supports the
mii-ioctls, and I found that the host resources mib (hosts/hr_network.c)
invokes
the if-mib's interface for every table iteration of the host mib (via the
Interface_Scan_Init and Next functions).
The problem that I discovered running this on my ARM hardware device is that
the constant polling of the MII Registers causes significant delay, and the
HOST mib entries will show up with e.g. 2-3 seconds delay. That again will
cause the snmpwalk to *choke* unless you specify a greater timeout value.
If you pay careful attention to the Interface_Scan_Init, it will dispose of the
container for interface statistics and create a new container which in case
triggers a full table re-load. Looking at the code for if-mib/ifTable, it uses
the cache api which prevents this abuse when browsing the IF-MIB. Also note the
comment from other developers: "ifTable container shouldn't change, so we
shouldn't have to re-fetch it every time"
I don't know of any API calls to cache a container in net-snmp. But a simple
guard (see patch below) did prevent the condition that I am seeing and the
snmpwalk finished without a problem. I am sure there are better ways to solve
this, but I really hope that there's a possibility resolving this issue with
this or an improved patch in future versions of net-snmp.
Best Regards,
- Eivind
+++
/work/enaess/neptune-mainline/tps/net-snmp/5.6.1/mainline/src/agent/mibgroup/if-mib/data_access/interface.c
2011-02-10 16:02:22.000000000 -0800
@@ -348,6 +348,7 @@
static netsnmp_iterator *it = NULL;
static netsnmp_container *c = NULL;
static netsnmp_interface_entry *e = NULL;
+static time_t tstamp;
/**
*
@@ -359,10 +360,16 @@
* ifTable container shouldn't change, so we shouldn' have to
* re-fetch it every time.
*/
+ if (tstamp < time(NULL))
+ {
if (NULL != c)
+ {
netsnmp_access_interface_container_free(c, 0);
+ }
c = netsnmp_access_interface_container_load(NULL, 0);
+ tstamp = time(NULL) + 5;
+ }
if (NULL != c) {
if (NULL != it)
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