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Date: Thu, 11 Sep 2014 17:35:27 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: linux-kernel@vger.kernel.org, Adrian Hunter <adrian.hunter@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Corey Ashford <cjashfor@linux.vnet.ibm.com>,
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        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Jean Pihet <jean.pihet@linaro.org>,
        Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
        Paul Mackerras <paulus@samba.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 13/14] tools lib fd array: Allow associating an integer
 cookie with each entry
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On Thu, Sep 11, 2014 at 12:23:30PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Sep 11, 2014 at 04:59:45PM +0200, Jiri Olsa escreveu:
> > On Thu, Sep 11, 2014 at 10:29:11AM -0300, Arnaldo Carvalho de Melo wrote:
> > > But then I had no use whatsoever for the ->ptr one at this point, so I
> > > just nuked it, to keep _just_ what is used _right now_, and added the
> > > comment to the changelog :-)
> > 
> > if we are treeting tools/lib/api as 'external' lib, I think we should
> > use 'void *' for priv and let the user retype it to whatever he wants
>  
> > but I dont care/insist here too much.. it just seems strange to me ;-)
> 
> Ok, so perhaps it should be:
> 
> 	struct fdarray {
> 		...
> 		union {
> 			int idx;
> 		} *priv;
> 		...
> }
> 
> And then perf's evlist will use:
> 
> 	fda->priv[fd].idx;
> 
> 	Then, when we get the need for a pointer, we can go there and
> add it to the union.
> 
> 	This will make tools/lib/api/fd/ a little bit more friendly to
> use outside the kernel sources, since then a new version will be source
> code compatible (but not necessarily binary compatible).

you lost me ;-)

could you please make an example of the !compatibility you mentioned?

> 	If we commit to that we can't just go on and change all its
> users as we can now do for things like 'struct sk_buff', 'struct sock'
> and any other kernel data structures.
> 	There are costs in making it 'external' in the sense you're
> implying. I want to make it a bit less 'external' (in your sense), at
> least while we initially implement new stuff like this one.

and the costs?


also I did not mean that union above, what I meant was:

struct fdarray {
	...
	void *priv;
	...
}


jirka