[Ksummit-2008-discuss] DTrace

[Christoph Hellwig]

On Sat, Jul 05, 2008 at 08:49:49AM -0500, James Bottomley wrote:
> To be fair, you can simply "just write" entry (jprobes) and return
> probes (kretprobes).  For the entry probes, if you want access to the
> function arguments you need to know the deep magic of the calling
> conventions of your platform (pretty easy on x86, though).

For jprobes your probe just has the same signature as the probed
function, and for kretprobes you use the regs_return_value()
arch-provided helper.  It's really quite easy and covers 90% of what
I need as a kernel developer.  Well, except for the cases where gcc
gets to smart and inlines enormous callchains, but at least in XFS
we've just delcared everything noinline..