linux-kernel - Re: [patch 1/4] Linux Kernel Markers

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Message-ID: <20071025191722.GA6114@Krystal>
Date:	Thu, 25 Oct 2007 15:17:22 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Roland McGrath <roland@...hat.com>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	systemtap@...rces.redhat.com,
	Christoph Hellwig <hch@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] Linux Kernel Markers - Architecture Independent Code

* Roland McGrath (roland@...hat.com) wrote:
> > I think the main issue with the solution you propose is that it doesn't
> > deal with markers in modules, am I right ?
> 
> My suggestion applies as well to modules as anything else.  
> What "like Module.symvers" means is something like:
> 
> name1	vmlinux		%s
> name2	fs/nfs/nfs	%d
> 
> All the modules built by the same kernel build go into this one file.
> 
> Modules packaged separately for the same kernel could provide additional
> files of the same kind.
> 
> > I will soon come with a marker iterator and a module that provides a
> > userspace -and in kernel- interface to enable/disable markers. Actually,
> > I already have the code ready in my LTTng snapshots. I can provide a
> > link if you want to have a look.
> 
> That's clearly straightforward to do given the basic markers data structures.
> 
> It does not address the need for an offline list of markers available in a
> particular kernel build or set of modules that you are not running right now.
> The approach now available for that is grovelling through the markers data
> structures extracted from vmlinux and .ko ELF files offline.  That is more
> work than one should have to do, and has lots of problems with coping with
> different packaging details, etc.
> 

Since gcc is required to build the systemtap probes on the development
marchine, I don't see why it would be much harder to also require prople
to install drawf ? Or maybe the "crash" tool ?

I guess you must already need to extract the symbols for your kprobes.
Do you use kallsyms for this ? The way I see it, you could maybe extract
kallsyms symbols corresponding to the markers data structures quite
easily.

I would rather prefer not to implement superfluous built-time data
extraction in the kernel build system just to make userspace simpler. If
we can leverage what currently exists, that would be better.

Mathieu

> 
> Thanks,
> Roland

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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