linux-kernel - Re: [PATCH 13/14] tools lib fd array: Allow associating an integer cookie with each entry

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Date:	Thu, 11 Sep 2014 17:35:27 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 13/14] tools lib fd array: Allow associating an integer
 cookie with each entry

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
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