Re: [GIT PULL] uprobes: pre-filtering

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2013-01-24 18:06:12]:

> On 01/24, Ingo Molnar wrote:
> >
> > * Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > > Unfortunately, currently there is no in-kernel user of
> > > pre-filtering.
> > >
> > > I'll try to implement the pid-base filtering at least for
> > > tracing/uprobe_events, but this needs a time. Not only I am
> > > not familiar with this code, I am not sure how this interface
> > > should actually look. And I agree, perf should be able to use
> > > it somehow, perhaps at least to allow to probe a single
> > > task/mm.
> >
> > Would be nice to get something minimal/simple going, so that it
> > can be tested, etc.
> 
> Heh, I understand.
> 
> I do not see anything simple to implement... I'll try to think.
> Srikar, do you have any idea?
> 
> All I can say right now: I'll send you the patches when I have them ;)
> Can't promise this will be soon.
> 
> _Perhaps_, as a first step, we can simply change create_trace_uprobe()
> so that it would be possible to specify list-of-pids at creation time...
> Not sure this actually makes sense.
> 

[ Adding Masami and Steven since they have other ideas / inputs ]

I can see two not-so-easy alternatives

Reuse the event's post filtering meta data and convert it to a
prefiltering handler. Convertion looks very tricky 

probe_event_enable() seems to be the right place to do this.
tu->call.filter would have the post filtering data
utc->filter needs to be set to the pre-filtering handler.

The other alternative is to extend the current abi and pass the
prefilter option. Should we extend the abi for userspace tracing is
obviously debatable.

> Oleg.
> 

-- 
Thanks and Regards
Srikar Dronamraju