> The complexity/difficulty of getting DTrace probes implemented depends
> on the type of probe. AFAIK the degree of difficulty looks like this
> ("1"=easy, "10"=godlike knowledge of universe required):
> 
> 1. "xtrace" probe (just prints what the "xtrace" mode of the shell would
> print)

Why is it useful to duplicate the functionality already provided by xtrace 
mode?
 
> 2. Trace subprocess creation and exit (e.g. fork())

Can't DTrace do it now using existing probes?
 
> 3. Trace subshell creation and destruction (subshell!=child process in
> ksh93)

Ditto.
 
> 4. Trace shell function calls

This seems like a real value for any interpreted language.
 
> 5. Trace calls to external commands and builtin commands

For builtins - yes. For external commands existing facilities may be 
sufficient.
 
- Alex Kolbasov


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