Usage of DTRACE_PROBE macro from sdt.h in kernel modules

[John-Mark Gurney]

Shrikanth Kamath wrote this message on Thu, Sep 04, 2014 at 02:23 -0700:
> On Wed, Sep 3, 2014 at 4:49 PM, Mark Johnston <markj at freebsd.org> wrote:
> > On Wed, Sep 03, 2014 at 02:09:48PM -0700, Shrikanth Kamath wrote:
> >> Thanks  Mark/Andriy for helping with this query. I checked the define
> >> KDTRACE_HOOKS define that is set. Rather I tried this, I defined a
> >> fake provider just to check if that prompts sdt_kld_load to create the
> >> SDT probes from my kernel module.
> >>
> >> + SDT_PROVIDER_DEFINE(fake);
> >> And it does help load the SDT probes I created, even though I am not
> >> using the fake provider I defined. I feel that sdt_kld_load is flawed
> >> when it is looking for sdt_providers_set in the module. It expects at
> >> least a provider define and cannot use one of the defined ones in
> >> kernel by just declaring it.
> >>
> >>          if (linker_file_lookup_set(lf, "sdt_providers_set", &begin,
> >> &end, NULL))
> >>              return;
> >
> > You're completely right; this issue was fixed in
> > http://svnweb.freebsd.org/base?view=revision&revision=267706
> >
> >>
> >> I intended to use DTRACE_PROBE() instead of the conventional
> >> SDT_PROBE_DEFINE/SDT_PROBE usage because I wanted to create probes
> >> which have probe names based on __LINE__ macro...disclaimer...this was
> >> just for experiment sakes...
> >>
> >> E.g
> >> func_foo()
> >> {
> >>     ....
> >>     if ()
> >>         return EINVAL;
> >>     ...
> >>     if ()
> >>         return EINVAL;
> >>     ...
> >>     if ()
> >>         return EINVAL;
> >> }
> >>
> >> which I replaced with
> >> func_foo()
> >> {
> >>     ...
> >>     if ()
> >>         RETSDT(func_foo, EINVAL);
> >>     ...
> >>     if ()
> >>         RETSDT(func_foo, EINVAL);
> >>     ...
> >>     if ()
> >>         RETSDT(func_foo, EINVAL);
> >> }
> >> where RETSDT macro and other macros are defined as
> >>
> >> #define PROBENAME1(func, __LINE__) func ## __LINE__
> >> #define PROBENAME(func, line) PROBENAME1(func, line)
> >>
> >> #define RETSDT(func, error_code)       \
> >>     do {                                                    \
> >>         DTRACE_PROBE(PROBENAME(func, __LINE__));\
> >>         return (error_code);               \
> >>     } while (0)
> >>
> >> With the fake provider I defined I get to see and execute my SDT probes
> >> % dtrace -l | grep func_foo
> >> 56455        sdt          netstack                 func_foo1592
> >>
> >> Here netstack is my module, and I have a probe name based on __LINE__
> >> which is 1592.
> >
> > Why not just use a single probe and make the line number and function
> > name arguments to the probe? That is, write something like
> >
> > #define RETSDT(error_code) do { \
> >         DTRACE_PROBE2(error__return, __func__, __LINE__)
> >         return (error_code);
> > } while (0)
> >
> Mark, for some reason using a single probe does not seem to fire the probe.

I'm doing something similar in my code:
cryptodev.c:SDT_PROBE_DEFINE1(opencrypto, dev, ioctl, error, "int"/*line number*/);
cryptodev.c:            SDT_PROBE1(opencrypto, dev, ioctl, error, __LINE__);

and it worked for me...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."