systemtap tracepoint support

[Josh Stone <jistone at redhat dot com>]

Hi All,

I just pushed out support for kernel tracepoints in systemtap -- a copy 
of the manpage section is included below for reference.  Try this 
command to see what's available in your kernel:
  stap -l 'kernel.trace("*")'

On Fedora rawhide, the kernel does have tracepoints enabled, but the 
kernel-devel package is missing the headers needed to define the 
tracepoints.  This has been fixed in the package spec now, so the next 
kernel package should be ready to go.  If you're impatient, you can also 
grab the source rpm and copy include/trace into
/usr/src/kernels/$(uname -r)/include/trace/.

RHEL5 U3 also contains tracepoints, and is also missing the headers from 
kernel-devel.  Again, copying the files from the source RPM should let 
you use them now.  I don't have an ETA for when the official package 
might be updated though...

For other distributions or custom kernels, YMMV, but anything 2.6.28+ 
should have at least a few tracepoints available.

As always, any feedback is welcome...

Thanks,

Josh


TRACEPOINTS

This  family  of  probe points hooks up to static probing trace-
points inserted into the kernel or modules.   As  with  markers,
these tracepoints are special macro calls inserted by kernel de-
velopers to make probing faster  and  more  reliable  than  with
DWARF-based  probes,  and DWARF debugging information is not re-
quired to probe tracepoints.  Tracepoints have an  extra  advan-
tage of more strongly-typed parameters than markers.

Tracepoint  probes  begin  with kernel.  The next part names the
tracepoint itself: trace("name").  The tracepoint  name  string,
which  may  contain  the  usual  wildcard characters, is matched
against the names defined by the kernel developers in the trace-
point header files.

The  handler  associated  with a tracepoint-based probe may read
the optional parameters specified at the macro call site.  These
are named according to the declaration by the tracepoint author.
For example, the tracepoint  probe  kernel.trace("sched_switch")
provides the parameters $rq, $prev, and $next.  If the parameter
is a complex type, as in a struct pointer, then a script can ac-
cess  fields  with  the  same syntax as DWARF $target variables.
Also, tracepoint parameters cannot be modified, but in guru-mode
a script may modify fields of parameters.

The  name of the tracepoint is available in $$name, and a string
of name=value pairs for all  parameters  of  the  tracepoint  is
available in $$vars.