RE: Question about netsnmp_call_handlers() function in snmp_agent.c

Ok, got it, I think I missed the "old_api" part. Thanks a lot Dave, I
appreciate your great help.

Best,
Yong Chen=20

-----Original Message-----
From: Dave Shield [mailto:D.T.Shield@csc.liv.ac.uk]=20
Sent: Thursday, December 08, 2005 1:18 AM
To: Yong Chen (yongche)
Cc: net-snmp-users@lists.sourceforge.net
Subject: RE: Question about netsnmp_call_handlers() function in
snmp_agent.c

On Wed, 2005-12-07 at 16:02 -0800, Yong Chen (yongche) wrote:
> 1. where do you populate treecache for a SET request?
> Is it "netsnmp_add_varbind_to_cache"? And is it the place that you=20
> combine all varbinds having the same handler into one "requests"

I think so, yes.
I'm not very familiar with that code (and don't have the time to read it
carefully), but a brief scan seems to indicate that this is probably
where most of the work is done.

> This func is not very easy to understand.

A little more high-level comments might be useful, certainly.
I suggest you ask your vendor for a refund :-)



> 2. As I mentioned, I'm actually using 4.x style So for my case, do I=20
> still have varbinds combined?

No.
As I said yesterday, the v4 model processes each varbind separately - so
your write method will be called once for each varbind in the request
(per pass)
But see below.


> 3. Since I'm not using 5.x handler API, do you consider=20
> "my_write_method" as a handler?... how is my_write_method called in=20
> 5.x agent?

OK - now you're getting more into the detailed internal implementation
nitty-gritty.

v4-style MIB modules (within a v5 agent) are handled by the 'old_api'
helper (see 'helpers/old_api.c' - and in particular
'netsnmp_old_api_helper()') Basically, this maps v5 handler-style
processing into the previous get_*/write_* routines.

So returning to your second question:


> For a SET pdu like:
>=20
> set my_table.a=3D1, my_table.b=3D2, my_table.c=3D3
>=20
> How many times will netsnmp_call_handlers() be called?

"netsnmp_call_handlers" will be called once (I think), which will pass
all three varbinds down the handler chain to 'netsnmp_old_api_helper'.
This will then call 'get_mytable' three times, followed by
'write_mytable_X' three times for each SET pass.

OK?

Dave


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