Re: Cache helper doesn't work with cross-compiled net-snmp-5.7.2.1

Hi,

I haven't managed to find the reason why the cache helper
implementation of the net-snmp-5.7.2.1 doesn't work properly in my
application.

I've cross-compiled the net-snmp-5.6.2.1 version, using the
arm-linux-gcc 4.5.1, and my sub-agent works fine.

When I compared the code of the cache helper implementation in the
net-snmp 5.7.2.1 with 5.6.2.1 I found out that the netsnmp_cache
structure of the net-snmp  5.7.2.1 contains a new variable: int
refcnt. This variable is used in the
netsnmp_cache_handler_owns_cache() function.
Does anybody can explain me how should I use this function in the
source code which I mentioned in my previous message?

I don't exactly understand why, but when I simply add the "refcnt"
variable into the  netsnmp_cache structure definition
(cache_handler.h) of the net-snmp 5.6.2.1 (with which my application
works) and recompiled it, the sub-agent crashed.

Does the net-snmp support the cross-compilation with arm-linux-gcc?
Maybe somebody knows which kind of tests from the net-snmp have to
show the result of the correct cache helper work?

Thanks in advance,
Ekaterina

On 3/31/14, Ekaterina Potachits <[email protected]> wrote:
> Hi All,
>
> I built the last version of the net-snmp-5.7.2.1 using the
> arm-linux-gcc compiler with the following flags:
> CC=arm-linux-gcc ./configure --target=arm-linux --host=arm-linux --build=x86
> \.
> --program-prefix=/usr --prefix=/usr --exec-prefix=/usr --with-endianness=big
> \.
> --enable-privacy --enable-des --enable-md5 --without-rpm --enable-shared \
> --with-cflags="-O2 -fsigned-char -I$WORKSPACE/Build/target/usr/include" \
> --with-persistent-directory=/var/net-snmp --with-copy-persistent-files="no"
> \
> --with-out-mib-modules="ucd_snmp notification notification-log-mib
> target utilities  disman/event disman/schedule host" \.
> --sysconfdir=/conf  --with-openssl=internal  --disable-embedded-perl \.
> --disable-perl-cc-checks --with-perl-modules=no
> --with-sys-contact=root@localhost \
> --disable-manuals --disable-scripts --disable-applications
> --disable-mibs --disable-mib-loading \
> --disable-deprecated --enable-ipv6 --with-default-snmp-version="3" \.
> --with-sys-location="Unknown" --with-logfile=/var/log/snmpd.log
> --with-security-modules="usm tsm"
>
> The cross-compiled net-snmp libraries I use in my sub-agent implementation.
> And it seems that the cache helper doesn't work in my case.
> Before I decided to use the  net-snmp-5.7.2 I use the  net-snmp-5.4.3
> and everything works fine.
>
> My sub-agent uses the cache mechanism to update the particular MIB
> table before the GET/GETNEXT request comes.
> In my case the first calling of the cache load works fine but after
> the cache timeout expires the sub-agents crashes with segmentation
> fault and the snmpwalk command gets the message: "Error in packet.
> Reason: (genError) A general failure occured Failed object:
> iso.3.6.1.4.1.231.2.10.2.2.10.3.1."
>
> I analysed the core dump of my application with gdb and it shows, that
> sub-agent crashes in the _cache_load () when it tries to call the
> _cache_free().
>
> Maybe somebody can help me and explain what is wrong?
>
> I have the following code:
>
>   struct ManagementNodeTable_entry {
>   long mnUnitId;
>   long mnNodeNr;
>   ...
> };
>
>
> #define MANAGEMENTNODETABLE_TIMEOUT  10
>
>
> initialize_table_ManagementNodeTable(void)
> {
>   oid ManagementNodeTable_oid[] = { 1, 3, 6, 1, 4, 1, 231, 2, 10, 2,
> 2, 10, 3, 1 };
>   size_t ManagementNodeTable_oid_len = OID_LENGTH(ManagementNodeTable_oid);
>   netsnmp_tdata  *table_data = NULL;
>   netsnmp_handler_registration *reg;
>   netsnmp_table_registration_info *table_info;
>   netsnmp_cache  *cache;
>   reg = netsnmp_create_handler_registration("ManagementNodeTable",
>                                             ManagementNodeTable_handler,
>                                             ManagementNodeTable_oid,
>                                             ManagementNodeTable_oid_len,
>                                             HANDLER_CAN_RONLY);
>   table_data = netsnmp_tdata_create_table("ManagementNodeTable", 0);
>   if (NULL == table_data) {
>     snmp_log(LOG_ERR,
>              "error creating tdata table for ManagementNodeTable\n");
>     return;
>   }
>
>   cache = netsnmp_cache_create(MANAGEMENTNODETABLE_TIMEOUT,
>                                ManagementNodeTable_load,
>                                ManagementNodeTable_free,
>                                ManagementNodeTable_oid,
>                                ManagementNodeTable_oid_len);
>   if (NULL == cache) {
>     snmp_log(LOG_ERR,
>              "error creating cache for ManagementNodeTable\n");
>     return;
>   }
>   else {
>     cache->magic = (void *) table_data;
>     cache->flags |= (NETSNMP_CACHE_DONT_FREE_BEFORE_LOAD |
> NETSNMP_CACHE_DONT_FREE_EXPIRED | NETSNMP_CACHE_DONT_AUTO_RELEASE);
>   }
>
>   table_info = SNMP_MALLOC_TYPEDEF(netsnmp_table_registration_info);
>   if (NULL == table_info) {
>     snmp_log(LOG_ERR,
>              "error creating table info for ManagementNodeTable\n");
>     return;
>   }
>   netsnmp_table_helper_add_indexes(table_info,
>                                    ASN_INTEGER,   /* index: mnUnitId */
>                                    ASN_INTEGER,   /* index: mnNodeNr */
>                                    0);
>
>   table_info->min_column = COLUMN_MNUNITID;
>   table_info->max_column = COLUMN_UNITNODECONTROLLERFWVERSION;
>   netsnmp_tdata_register(reg, table_data, table_info);
>
>   if (cache) {
>     netsnmp_inject_handler (reg,
>                             netsnmp_cache_handler_get(cache)
>                            );
>   }
> }
>
>
> /** Create a new row in the table */
> netsnmp_tdata_row *
> ManagementNodeTable_createEntry (netsnmp_tdata *table_data,
>                                  struct ManagementNodeTable_entry
> *srcEntry)
> {
>   struct ManagementNodeTable_entry *destEntry;
>   netsnmp_tdata_row *row;
>
>   destEntry = SNMP_MALLOC_TYPEDEF (struct ManagementNodeTable_entry);
>   if (!destEntry)
>     return NULL;
>   row = netsnmp_tdata_create_row();
>   if (!row) {
>     SNMP_FREE (destEntry);
>     return NULL;
>   }
>
>   memcpy (destEntry, srcEntry, sizeof (struct ManagementNodeTable_entry));
>   row->data = destEntry;
>
>   netsnmp_tdata_row_add_index (row, ASN_INTEGER,
>                                &(destEntry->mnUnitId),
>                                sizeof(destEntry->mnUnitId));
>   netsnmp_tdata_row_add_index (row, ASN_INTEGER,
>                                &(destEntry->mnNodeNr),
>                                sizeof(destEntry->mnNodeNr));
>   if (table_data) {
>     netsnmp_tdata_add_row( table_data, row );
>   }
>
>   return row;
> }
>
>
> /** Cache handling */
> int
> ManagementNodeTable_load(netsnmp_cache * cache, void *vmagic)
> {
>   netsnmp_tdata  *table = (netsnmp_tdata *) cache->magic;
>   struct ManagementNodeTable_entry mnNodeEntry;
>
>   if (table != NULL) {
>     netsnmp_tdata_row *row;
>
>     // Call functions to fill the ManagementNodeTable_entry structure.
>     // Update ManagementNodeTable table
>     ....
>     row = ManagementNodeTable_createEntry (table, &mnNodeEntry);
>   }
>   return 0;
> }
>
>
> void
> ManagementNodeTable_free(netsnmp_cache * cache, void *vmagic)
> {
>   netsnmp_tdata  *table = (netsnmp_tdata *) cache->magic;
>   netsnmp_tdata_row *row;
>
>   // remove all existing rows
>   while ( netsnmp_tdata_row_count(table) > 0 )
>   {
>     struct ManagementNodeTable_entry *entry;
>     row = netsnmp_tdata_row_first( table );
>     entry = (struct ManagementNodeTable_entry *) row->data;
>     SNMP_FREE(entry);
>     netsnmp_tdata_remove_and_delete_row( table, row );
>   }
> }
>
>
> /** Handles requests for the ManagementNodeTable table */
> int
> ManagementNodeTable_handler(netsnmp_mib_handler *handler,
>                             netsnmp_handler_registration *reginfo,
>                             netsnmp_agent_request_info *reqinfo,
>                             netsnmp_request_info *requests)
> {
>   netsnmp_request_info *request;
>   netsnmp_table_request_info *table_info;
>   struct ManagementNodeTable_entry *table_entry;
>   DEBUGMSGTL(("ManagementNodeTable:handler",
>               "Processing request (%d)\n", reqinfo->mode));
>
>   switch (reqinfo->mode) {
>   /* Read-support (also covers GetNext requests) */
>   case MODE_GET:
>     for (request = requests; request; request = request->next) {
>       if (request->processed)
>         continue;
>       table_entry = (struct ManagementNodeTable_entry *)
> netsnmp_tdata_extract_entry(request);
>       table_info = netsnmp_extract_table_info(request);
>
>       switch (table_info->colnum) {
>       case COLUMN_MNUNITID:
>         if (!table_entry) {
>           netsnmp_set_request_error(reqinfo, request,
>                                     SNMP_NOSUCHINSTANCE);
>           continue;
>         }
>         snmp_set_var_typed_integer(request->requestvb, ASN_INTEGER,
>                                    table_entry->mnUnitId);
>         break;
>       case COLUMN_MNNODENR:
>         if (!table_entry) {
>           netsnmp_set_request_error(reqinfo, request,
>                                     SNMP_NOSUCHINSTANCE);
>           continue;
>         }
>         snmp_set_var_typed_integer(request->requestvb, ASN_INTEGER,
>                                    table_entry->mnNodeNr);
>         break;
>
>         ....
>
>         default:
>         netsnmp_set_request_error(reqinfo, request,
>                                   SNMP_NOSUCHOBJECT);
>         break;
>       }
>     }
>     break;
>
>   }
>   return SNMP_ERR_NOERROR;
> }
>
>
> Thanks,
> Ekaterina
>

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