Re: Language Reference, updated

[Robb Romans <robb at linux dot vnet dot ibm dot com>]

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>>>>> "FCHE" == Frank Ch Eigler <fche@redhat.com> writes:

Hi Frank, thanks for the reply.

    MM> Section 3.6 Mention use of the deref() macro in embedded C for
    MM> safety.  Give an example.
    >>  I could use a little help with this. Would anyone be able to
    >> provide a good working example?

    FCHE> There are examples in the tapset.

Sorry, do you mean there are specific examples of how to use the deref
macro? I didn't find any. 

    FCHE> Josh switched us over to the "kread" function:

    FCHE> function _struct_timeval:string(addr:long) %{ /* pure */
    FCHE> struct timeval *tv = (struct timeval *)(unsigned
    FCHE> long)THIS->addr;

    FCHE> if (tv == NULL) strlcpy (THIS->__retvalue, "NULL",
    FCHE> MAXSTRINGLEN); else snprintf(THIS->__retvalue, MAXSTRINGLEN,
    FCHE> "[%ld.%06ld]", kread(&(tv->tv_sec)), kread(&(tv->tv_usec)));
    FCHE> %}

OK, kread replaces deref? I can certainly insert this example, but I
really don't know how to document it in the Guide.

    FCHE> (However, it is not clear that the NULL-handling case is
    FCHE> relevant or appropriate.  If the timeval* coming in from the
    FCHE> application is permitted to be NULL, fine, but if it's meant
    FCHE> as a crash-prevention mechanism in this embedded-C routine,
    FCHE> then it's not right.)

If you don't know, then I certainly don't either :)

    >> [...]
    MM> Sections 8.4.1 - 8.4.3 Show examples of the output that results
    MM> from using these functions.
    >>  I'd like to be provided with self-contained examples that I can
    >> document, run and capture the output.

    FCHE> If you have a working systemtap build, it should not be hard
    FCHE> to make such examples yourself.  Its ease-of-use is the stuff
    FCHE> of legend ... or in any case well tested by newbie users.

Right, but several runs have resulted in hard lockups of my poor
workstation and I got tired of that very fast. You will see that I have
provided output in a few more of the examples in the Guide. I get your
point, but illustrative examples provided by experts in SystemTap in the
remaining areas would be helpful, IMHO.

    MM> Section 9.2.21 Explain what is meant by the "target process."
    >>  Does this mean the PID of the program being probed?

    FCHE> Sort of - see the "-c PROGRAM" and "-x PID" stap options.  The
    FCHE> man page for "-c" should be clarified to point out that the
    FCHE> target() stapfuncs.5 function is set analogously to the -x
    FCHE> case.

Please check the Guide and see if what I included is sufficient.

Here's the latest version.

Attachment: SystemTap-Language-Ref-20070222.tex.gz
Description: SystemTap-Language-Ref-20070222.tex.gz

Attachment: SystemTap-Language-Ref-20070222.ps.gz
Description: SystemTap-Language-Ref-20070222.ps.gz

Regards,
Robb

- -- 
Robb Romans                     (512) 838-0419
Linux Commando                  T/L   678-0419
robb@linux.vnet.ibm.com         ARS NA5TT
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