Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

["Frank Ch. Eigler" <fche@redhat.com>]

Hi -

On Sat, Mar 21, 2009 at 05:04:22AM -0700, Andrew Morton wrote:
> [...]
> > There have been many mixed messages from LKML on the topic - sometimes
> > mentioning systemtap is forbidden, other times necessary.  Sorry about
> > that.
> 
> heh.  We all love systemtap and want it to get better.

Great!


> [...]
> I have strong memories of being traumatised by reading the uprobes
> code.  What's the story on all of that nowadays?

uprobes, being a layer upon utrace that provides a kprobes-like
breakpointing API for user threads, is being refactored into several
parts.  I don't know about the aesthetics of it all, but I believe the
general future plan is this:

One piece would perform machine code analysis (to classify
instructions for ideal/safe placement of breakpoints or for code
patching), and another thin layer that uses this and utrace to manage
user-space breakpoints.  (Systemtap would interface at this point.)
Then a user-space syscallish interface could come along to expose this
to a super-ptrace client (to speed up gdb; perhaps to allow multiple
debuggers).  Plus one might as well add an ftrace-engine for it
(directly analogous to the recent kprobe-based one that ftrace people
found "cool".)


> > > Actually it seems that the whole utrace-ftrace thing is a big
> > > distraction and could/should just be omitted.  This is a systemtap
> > > feature and should be viewed as such. [...]
> > 
> > utrace is a better way to perform user thread management than what is
> > there now, and the utrace-ftrace widget shows how to *hook* thread
> > events such as syscalls in a lighter weight / more managed way than
> > the first one proposed.  (That's one reason we've been participating
> > in the ftrace discussions.)  Of course it can be made to use the fine
> > syscall pretty-printing code recently added.
> 
> eh.  Boring.  Let's fix systemtap?

There are several constituencies here, some of which find the above
exciting.  That's OK and we'd like to help them too.


- FChE