dtrace discuss - Dec 2007 - determining the type of arg entries?

In order to print the arguments to a syscall probe, I''m having
to hard code the processing in advance.  Although what I really
want is a to_string() function that "does the right thing", I
was wondering if I could hack something up using the ?: operator.

If I had a way to find out the type of an arg[] entry, I could
process it differently, depending on whether it was a string or
a number.  Sadly, I don''t see anything of this sort.  Help?

-r
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http://www.cfcl.com/rdm            Rich Morin
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On Sat, Dec 22, 2007 at 02:09:47PM -0800, Rich Morin
wrote:
> In order to print the arguments to a syscall probe, I''m having
> to hard code the processing in advance.  Although what I really
> want is a to_string() function that "does the right thing", I
> was wondering if I could hack something up using the ?: operator.
> 
> If I had a way to find out the type of an arg[] entry, I could
> process it differently, depending on whether it was a string or
> a number.  Sadly, I don''t see anything of this sort.  Help?
> 
> -r
args[] provides the proper types automatically when the provider
describes the types, but we haven''t done that for syscall yet.
There are a couple of problems to be solved there:

(a) a canonical description of the syscall types
(b) support for sub-sys calls as part of syscall

We could also provide the magic to_string(), but I would consider
that dependent to the above -- it would have to be able to
reliably know the args[] types in order to work.  Sorry we don''t
have a better answer yet.

At the moment, your best bet is simply trace(), which does include a
simple heuristic for formatting the data appropriately:

# dtrace -s /dev/stdin
BEGIN {
trace(3);
trace("hello");
trace(`kmem_flags);
}
^D
dtrace: script ''/dev/stdin'' matched 1 probe
CPU     ID                    FUNCTION:NAME
  1      1                           :BEGIN         3  hello   15

but of course unlike printf you can''t control the output.

-Mike

-- 
Mike Shapiro, Solaris Kernel Development. blogs.sun.com/mws/