Re: working with tables...

#1 (**permalink**) 04-17-2008

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Ok...using gdb I found where my code crashes. In the handler function that
follows

MonThreadsTable_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;
MonThreadsTable_entry *table_entry=NULL;
char arreglo[300];

switch (reqinfo->mode) {
/*
* Read-support (also covers GetNext requests)
*/
case MODE_GET:
for (request=requests; request; request=request->next) {
table_entry = (MonThreadsTable_entry *)
netsnmp_extract_iterator_context(request);
if(table_entry==NULL)
DEBUGMSGTL(("MonThreadsTable","NULL POINTER"));
.......

the function netsnmp_extract_iterator_context(request) returns a null
pointer instead of a pointer to the first
entry of my list. I checked and my linked list is being generated and
updated correctly (I'm printing each entry values constantly), so I guess
I'm missing something at initialization time....here's my initialization
function.

void
initialize_table_MonThreadsTable(void)
{
static oid MonThreadsTable_oid[] = {1,3,6,1,4,1,17723,2,1,1,19,1};
size_t MonThreadsTable_oid_len = OID_LENGTH(MonThreadsTable_oid);
netsnmp_handler_registration *reg;
netsnmp_iterator_info *iinfo;
netsnmp_table_registration_info *table_info;

reg = netsnmp_create_handler_registration(
"MonThreadsTable", MonThreadsTable_handler,
MonThreadsTable_oid, MonThreadsTable_oid_len,
HANDLER_CAN_RONLY
);

table_info = SNMP_MALLOC_TYPEDEF( netsnmp_table_registration_info );
netsnmp_table_helper_add_indexes(table_info,
ASN_INTEGER, /* index: IdThread */
0);
table_info->min_column = 1;
table_info->max_column = 4;

iinfo = SNMP_MALLOC_TYPEDEF( netsnmp_iterator_info );
iinfo->get_first_data_point = MonThreadsTable_get_first_data_point;
iinfo->get_next_data_point = MonThreadsTable_get_next_data_point;
iinfo->table_reginfo = table_info;

netsnmp_register_table_iterator( reg, iinfo );

/* Initialise the contents of the table here */
}

Do you see someting wrong??? How do I link my table with the request info
used by the netsnmp_extract_iterator_context function??

Thanks again,

Alejandro

On Thu, Apr 17, 2008 at 11:00 AM, Alejandro Islas <alex.islas@gmail.com>
wrote:

>
>
> On Thu, Apr 17, 2008 at 3:47 AM, Dave Shield <D.T.Shield@liverpool.ac.uk>
> wrote:
>
> > On 17/04/2008, Alejandro Islas <alex.islas@gmail.com> wrote:
> > > I tried to use mib2c.container.conf file but mib2c
> > > wasn't able to found it
> >
> > Hmmm... what version of the toolkit are you using?
> > mib2c.container.conf has been around since the 5.2 release
> > (although the internals have changed significantly since then).
> >
> > I'm using NET-SNMP version: 5.2.1.2
> >
> >
> > > 1)After using mib2c my .c file only contains create/remove entries
> > > functions. As far as I understand, I need to implement a fetch entrie,
> > to
> > > avoid duplicate row entries..correct???
> >
> > Sorry - I don't understand what you're asking here.
> >
>
> After using mib2c to generate my code, I noticed that it created a
> create_row_entry and a
> remove_row_entry functions. I implemented a fetch_row_entry, so that
> my code would be able to check
> if it doesn't have a previously created entry for a particular index.
>
> >
> >
> > > 2) Besides including data reading functions (i'm using text files),
> >
> > What do you mean by "data reading functions"?
> > How are you storing the table contents within your module?
>
>
> I read a text file created by another process. Each line of such text
> file contains a row's info
> of my table, so my process checks for such entry(using the index) in
> the linked list and updated it or create a new entry
> if its the first time I received inf of such row.
>
> >
> >
> > > do I need to do anything else?? I did not do anything to the handler,
> > > get_first_data_point and get_next_data_point functions, I left them as
> > mib2
> > > generated them.
> >
> > The get_{first,next}_data_point routines need to step through the
> > rows of your table - in whatever way is appropriate for your module.
> > The template code assumes that the table is held as a linked list
> > of individual row entries - if this is how your data reading functions
> > store the table, then you probably don't need to change this code
> > much (if at all).
> > If you are storing the table in a different manner (or pulling it from
> > external sources), then you will need to amend these two routines
> > to match.
>
>
> Yes, I'm using the linked list of individual row entries created by
> mib2c.
>
> >
> >
> > > 3) Could you explain (or send me an info link) of how my table
> > handler is
> > > called by the system?? I don't see where my table list is called on
> > it.
> >
> > When you register the table, the agent includes this information in
> > a list of all the OIDs that it knows about. When it receives a
> > request,
> > it searches this list for the appropriate match(es), and calls the
> > corresponding handlers.
> >
> >
> > > 4) I used gdb...but didn't help me a lot, it only confirmed a
> > segmentation
> > > fault.
> >
> > But it should also indicate *where* this segmentation fault occurs.
> > This would help track down what is causing it.
>
>
> You're right, I think I need to play a little bit more with gbd
>
> >
> >
> > > I'm not compiling the whole project, only adding my so files using
> > > dlmod command. Can I still use dbg using this method or do I need to
> > compile
> > > the whole deamon including my handlers???
> >
> > Ummm... not sure.
> > It would probably be sensible to start by working with a "traditional"
> > approach,
> > at least until you get the module working. The same module code can be
> > embedded within the main agent, loaded dynamically, or used within a
> > subagent - with no changes to the code.
> >
>
> I'll try this and let you know.
>
> Alejandro
>
>

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Ok...using gdb I found where my code crashes. In the handler function that follows<br><br>MonThreadsTable_handler(<br> & nbsp;  netsnmp_mib_handler     & nbsp;       &nb sp; *handler,<br>    netsnmp_handler_registration   &nbs p;  *reginfo,<br>    netsnmp_agent_request_info         *reqinfo,<br>
    netsnmp_request_info             &nbsp ; *requests) {<br><br>    netsnmp_request_info        *request;<br>    netsnmp_table_request_info *table_info;<br>    MonThreadsTable_entry    &nbsp ;     *table_entry=NULL;<br>    char arreglo[300];<br>
<br>    switch (reqinfo->mode) {<br>        /*<br>       &nb sp; * Read-support (also covers GetNext requests)<br>      & nbsp;  */<br>    case MODE_GET:<br>      & nbsp; for (request=requests; request; request=request->next) {<br>       &nb sp;    table_entry = (MonThreadsTable_entry *)<br>
        &n bsp;       &nbs p;              netsnmp_extract_iterator_context(request);<br>&nbs p;            if(table_entry==NULL)<br>    & nbsp;           DEBUGMSGTL(("MonThreadsTable","NULL POINTER"));<br>......<br><br> the function netsnmp_extract_iterator_context(request) returns a null pointer instead of a pointer to the first<br>
entry of my list. I checked and my linked list is being generated and updated correctly (I'm printing each entry values constantly), so I guess I'm missing something at initialization time....here's my initialization function.<br>
<br>void<br>initialize_table_MonThreadsTable(void) <br>{<br>    static oid MonThreadsTable_oid[] = {1,3,6,1,4,1,17723,2,1,1,19,1};<br>  &nb sp; size_t MonThreadsTable_oid_len   = OID_LENGTH(MonThreadsTable_oid);<br>  &n bsp; netsnmp_handler_registration    *reg;<br>
    netsnmp_iterator_info    &nbsp ;      *iinfo;<br>    netsnmp_table_registration_info *table_info;<br><br>    reg = netsnmp_create_handler_registration(<br> &nbs p;             "MonThreadsTable",   &nbs p; MonThreadsTable_handler,<br>
        &n bsp;     MonThreadsTable_oid, MonThreadsTable_oid_len,<br>   &nbs p;           HANDLER_CAN_RONLY<br>    &nbsp ;       &nbsp ; );<br><br>    table_info = SNMP_MALLOC_TYPEDEF( netsnmp_table_registration_info );<br>    netsnmp_table_helper_add_indexes(table_info,<br>
        &n bsp;       &nbs p;           ASN_INTEGER,  /* index: IdThread */<br>       &nbs p;                 &n bsp;  0);<br>    table_info->min_column = 1;<br>    table_info->max_column = 4;<br>    <br>    iinfo = SNMP_MALLOC_TYPEDEF( netsnmp_iterator_info );<br>
    iinfo->get_first_data_point = MonThreadsTable_get_first_data_point;<br> &nb sp;  iinfo->get_next_data_point  = MonThreadsTable_get_next_data_point;<br> &nbs p;  iinfo->table_reginfo     &nb sp;  = table_info;<br>    <br>    netsnmp_register_table_iterator( reg, iinfo );<br>
<br>    /* Initialise the contents of the table here */<br>}<br><br>Do you see someting wrong??? How do I link my table with the request info used by the netsnmp_extract_iterator_context function??<br><br>Thanks again,<br>
<br>Alejandro<br><br><br><div class="gmail_quote">On Thu, Apr 17, 2008 at 11:00 AM, Alejandro Islas <<a href="mailto:alex.islas@gmail.com">alex.islas@gmai l.com</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br><br><div class="gmail_quote"><div class="Ih2E3d">On Thu, Apr 17, 2008 at 3:47 AM, Dave Shield <<a href="mailto:D.T.Shield@liverpool.ac.uk" target="_blank">D.T.Shield@liverpool.ac.uk</a>> wrote:<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d">
<div>On 17/04/2008, Alejandro Islas <<a href="mailto:alex.islas@gmail.com" target="_blank">alex.islas@gmail.com</a>> wrote:<br>
> I tried to use mib2c.container.conf file but mib2c<br>
> wasn't able to found it<br>
<br>
</div>Hmmm... what version of the toolkit are you using?<br>
mib2c.container.conf has been around since the 5.2 release<br>
(although the internals have changed significantly since then).<br>
</div><div><br>
<font color="#cc33cc">I'm using NET-SNMP version:  <a href="http://5.2.1.2" target="_blank">5.2.1.2</a><br></font><div class="Ih2E3d"><br>
<br>
>  1)After using mib2c my .c file only contains create/remove entries<br>
> functions. As far as I understand, I need to implement a fetch entrie, to<br>
> avoid duplicate row entries..correct???<br>
<br>
</div></div><div class="Ih2E3d">Sorry - I don't understand what you're asking here.</div></blockquote><div><br>    <font color="#cc33cc">After using mib2c to generate my code, I noticed that it created a create_row_entry and a <br>
    remove_row_entry functions. I implemented a fetch_row_entry, so that my code would be able to check<br>
    if it doesn't have a previously created entry for a particular index.<br></font></div><div class="Ih2E3d"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

<br>
<div><br>
> 2) Besides including data reading functions (i'm using text files),<br>
<br>
</div>What do you mean by "data reading functions"?<br>
How are you storing the table contents within your module?</blockquote></div><div><br>   <font color="#cc33cc">I read a text file created by another process. Each line of such text file contains a row's info<br>   of my table, so my process checks for such entry(using the index) in the linked list and updated it or create a new entry<br>

  if its the first time I received inf of such row.<br></font></div><div class="Ih2E3d"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>

<div><br>
> do I need to do anything else?? I did not do anything to the handler,<br>
> get_first_data_point and get_next_data_point functions, I left them as mib2<br>
> generated them.<br>
<br>
</div>The get_{first,next}_data_point routines need to step through the<br>
rows of your table - in whatever way is appropriate for your module.<br>
The template code assumes that the table is held as a linked list<br>
of individual row entries - if this is how your data reading functions<br>
store the table, then you probably don't need to change this code<br>
much (if at all).<br>
  If you are storing the table in a different manner (or pulling it from<br>
external sources), then you will need to amend these two routines<br>
to match.</blockquote></div><div><br>   <font color="#cc33cc">Yes, I'm using the linked list of individual row entries created by mib2c.</font><br></div><div class="Ih2E3d"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

<br>
<div><br>
>  3) Could you explain (or send me an info link) of how my table handler is<br>
> called by the system?? I don't see where my table list is called on it.<br>
<br>
</div>When you register the table, the agent includes this information in<br>
a list of all the OIDs that it knows about.   When it receives a request,<br>
it searches this list for the appropriate match(es), and calls the<br>
corresponding handlers.<br>
<div><br>
<br>
> 4) I used gdb...but didn't help me a lot, it only confirmed a segmentation<br>
> fault.<br>
<br>
</div>But it should also indicate *where* this segmentation fault occurs.<br>
This would help track down what is causing it.</blockquote></div><div><br>    <font color="#cc33cc">You're right, I think I need to play a little bit more with gbd</font> <br></div><div class="Ih2E3d"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

<br>
<div><br>
>  I'm not compiling the whole project, only adding my so files using<br>
> dlmod command. Can I still use dbg using this method or do I need to compile<br>
> the whole deamon including my handlers???<br>
<br>
</div>Ummm... not sure.<br>
It would probably be sensible to start by working with a "traditional" approach,<br>
at least until you get the module working.   The same module code can be<br>
embedded within the main agent, loaded dynamically, or used within a<br>
subagent - with no changes to the code.<br>
<font color="#888888"></font></blockquote></div><div> <br> <font color="#cc33cc">I'll try this and let you know.</font> <br></div><div><br><font color="#cc33cc">Alejandro</font> <br></div></div><br>
</blockquote></div><br>

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