what is a tapset? [RE: Skeleton detailed design document]

["Chen, Brad" <brad dot chen at intel dot com>]

Looking this over the draft paper, and thinking about Frank's 
note concerning script libraries, I started thinking about 
the first figure suggested in the draft. See my ASCII art 
below. Perhaps this is overly simplistic; is any of this 
incorrect? What parts are missing?

===========================================================

INPUT:  script
	     |
	     v
TOOLS: elaborator -> compiler ->   ld   -> mytap.ko
           ^             ^          ^
           |             |          |
	tapset defns       |       systemtap libs
	   		       |       tapset libs
			       |       kernel libs
				 |
		   /usr/include/systemtap/
		   /usr/include/systemtap/tapset/
               kernel symbolic information

EXECUTION:	insmod("mytap.ko") -> [kernel]
					[kjr]probes + trap handler
      	      	      systemtap runtime in kernel [needed?]
					user-level data handler 

===========================================================

Question: Can two taps "mytap1.ko" and "mytap2.ko" be loaded
in the kernel at the same time? If so, do they need to share 
anything besides kprobes? If they do, does the shared part 
need to be in the kernel instead of being linked statically 
into the ko? Maybe we started this discussion this morning
already...

Other tapset design questions:
- Do the tapset libraries need to be built with the kernel?
  [yes; they will reference kernel symbols that must be
   resolved statically]
- I believe kernel symbolic info will be needed during the
  compile of the elaborated script to deal with kernel data.
- Can a script refer directly to a kernel code symbol,
  or can it only do so via a tapset? It might be nice if
  jprobes were responsible for most/all resolution of kernel
  symbolic info.
- Systemtap scripts ought generally to be portable. Is there 
  any hope of making a mytap.ko that is portable across kernel
  builds and configurations? Is this an appropriate goal?
- The above flow suggests that a tapset consists of three
  pieces:
	- definitions for the elaborator. This would have
	  to define everything the elaborator would need
	  to know to translate a script
	- include files. APIs for the tapset's library as well
	  as possibly constants etc.
	- a tapset library. Code to initialize the tapset and
	  implement the taps. Some tapsets will use kprobes
	  directly; others might only reference other tapsets.

  Is this consistent with what other folks are thinking?
  I'm imaging that the script libraries described by Frank
  might actually compile into a tapset library.

Brad

-----Original Message-----
From: systemtap-owner@sources.redhat.com
[mailto:systemtap-owner@sources.redhat.com] On Behalf Of Vara Prasad
Sent: Thursday, March 31, 2005 12:48 AM
To: systemtap@sources.redhat.com
Subject: Skeleton detailed design document

Frank had started an initial design document but we have not done any 
updates to it after that.
I have taken Frank's document added few more sections that i think are 
relevant based on the
discussions we have been having. Once we think we got the basic sections

i will commit that
skeleton to the cvs. I am thinking people who are driving the individual

sections can fill them
up and commit to CVS so we will have more complete design document.

Please let me know your thoughts on the attached Linux text document.
If people prefer inline let me know i can make it inline.