linux-kernel - Re: [PATCHv9 2.6.35-rc4-tip 10/13] perf: Re-Add make_absolute

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Message-ID: <20100712172640.GD23776@linux.vnet.ibm.com>
Date:	Mon, 12 Jul 2010 22:56:40 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCHv9 2.6.35-rc4-tip 10/13]  perf: Re-Add make_absolute_path

> 
> > Actually we dont need to convert malloc@...c-2.5.so to a
> > malloc@...b/libc.so.6. Because we can match the shortname of the dso. 
> 
> Humm, I see, it is path based, so the first libc-2.5.so that appears in
> the LD_LIBRARY_PATH equivalent used in this code will be user, is that
> right?

No,  As you might have got it by reading patch 11. I am trying to
reuse the thread/session elements and walk thro the maps in the
map_groups. So I dont need to bother on LD_LIBRARY_PATH.
> 
> I.e. if I'm testing some new libc-2.5.so that provides, say, private
> futexes while the one in my distro still doesn't have this feature, I'll
> have to specify the absolute name or make sure it is before the system's
> libc-2.5.so in the LD_LIBRARY_PATH, right?

We get to the right one, as we walk the list of dsos in the
threadlist. But we have an option of either giving a correct full path
or the shortname for the dso without any path. However right now the
shortname has to be unique i.e I cant use malloc@...c instead of
malloc@...c-2.5.so. I would think specifying full path will be the most
probable usage case. However if a person refers /proc/<pid>/maps,
specifying shortnames should also be easy.

> 
> > Problem will occur when users specifies a full path of the file.
> > Since the file can refer to a symbolic link and the dso will have just
> > the short name or the target file name. Here I am using
> > make_absolute_path to resolve to the target file.
> > Now we can then either check on dso full names or short names.
> > I have chosen to use the short name.
> 
> Humm, so what you want is one of:
> 
> realpath - return the canonicalized absolute pathname
> canonicalize_file_name -  return the canonicalized filename
> 
> Can you please check the man pages for both before we decide
> re-introducing make_absolute_path?

right, realpath is right choice, I will use it instead of this patch. 


--
Thanks and Regards
Srikar

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