For historic reasons, the project we are working on is stuck using a
very old version of net-snmp (5.1.2). However, looking at the more
recent code, it looks like the problem I am seeing exists there too.
We recently made the transition from 32 bits to 64 bits, and I find that
under 64 bits, I can no longer snmpwalk our MIBs. I get lots of this in
the log when I try:
snmpd err send response: Error building ASN.1 representation (build int
size 4: s/b 8)
Looking at our code, I see that for rows in the MIB that are of type
INTEGER, we appropriately define fields in structs of type int. Then,
when we process an snmpget, we construct the variable with code like this:
[in some .h file]
int fred;
[actual code]
snmp_set_var_typed_value(var, ASN_INTEGER,
(u_char *) &fred,
sizeof(fred));
But later, deep in the net-snmp code, at the top of the routine
asn_build_int(), we fail this sanity test:
if (intsize != sizeof(long)) {
_asn_size_err(errpre, intsize, sizeof(long));
return NULL;
}
Now unless I am misunderstanding something, (and I hope I am) the
intsize here is the sizeof(fred) I passed into snmp_set_var_typed_value,
and in both 32 bit and 64 bit environments, that's 4 bytes (i.e.
sizeof(int)). But while under 32 bits, sizeof(long) is also 4, under 64
bits, sizeof(long) is 8 bytes. So under 64 bits, the sanity test in
asn_build_int() will always fail, and I see the error messages in my log
and my snmpwalk times out.
INTEGER is 4 bytes, now and forever, right? The ASN.1 protocol doesn't
change just because the underlying machine architecture changes. So
surely I should use a (4 byte) int in my internal structs to hold values
that are declared as INTEGER in the MIB files. But the code seems to
insist that I use longs, and pass them into snmp_set_var_typed_value()
as such. Is this so? If so, why? Please tell me I'm missing something
basic here. We have lots of incumbent structs with the INTEGERs defined
to be ints, not longs.
-John Gregg
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