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SubjectRe: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes
On Thu, Jan 14, 2010 at 12:43:01PM +0100, Peter Zijlstra wrote:
> On Thu, 2010-01-14 at 12:35 +0100, Frederic Weisbecker wrote:
> > On Thu, Jan 14, 2010 at 12:23:11PM +0100, Peter Zijlstra wrote:
> > > On Mon, 2010-01-11 at 17:56 +0530, Srikar Dronamraju wrote:
> > > > This patch implements ftrace plugin for uprobes.
> > >
> > > Right, like others have said, trace events is a much saner interface.
> > >
> > > So the easiest way I can see that working is to register uprobes against
> > > a file (not a pid). Then on creation it uses rmap to find all current
> > > maps of that file and install the probe if there is a consumer for that
> > > map.
> > >
> > > Then for each new mmap() of that file, we also need to check if there's
> > > a consumer ready and install the probe.
> >
> >
> >
> > That looks racy.
> >
> > Say you first create a probe on /bin/ls:
> >
> > perf probe p addr_in_ls /bin/ls
> >
> > then something else launches /bin/ls behind you, probe
> > is set on it
> >
> > then you launch:
> >
> > perf record -e "probe:...." /bin/ls
> >
> > Then it goes recording the previous instance.
>
> Uhm, why? Only the perf /bin/ls instance has a consumer and will thus
> have a probe installed.
>
> (Or if you want to use ftrace you need to always have all instances
> probed anyway)


I see, so what you suggest is to have the probe set up
as generic first. Then the process that activates it
becomes a consumer, right?

Would work, yeah.



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