From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756218AbaIKPt3 (ORCPT ); Thu, 11 Sep 2014 11:49:29 -0400 Received: from mail.kernel.org ([198.145.19.201]:34993 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751507AbaIKPt2 (ORCPT ); Thu, 11 Sep 2014 11:49:28 -0400 Date: Thu, 11 Sep 2014 12:49:22 -0300 From: Arnaldo Carvalho de Melo To: Jiri Olsa Cc: linux-kernel@vger.kernel.org, Adrian Hunter , Borislav Petkov , Corey Ashford , David Ahern , Frederic Weisbecker , Ingo Molnar , Jean Pihet , Jiri Olsa , Namhyung Kim , Paul Mackerras , Peter Zijlstra Subject: Re: [PATCH 13/14] tools lib fd array: Allow associating an integer cookie with each entry Message-ID: <20140911154922.GK10158@kernel.org> References: <1410358129-9965-1-git-send-email-acme@kernel.org> <1410358129-9965-14-git-send-email-acme@kernel.org> <20140911103319.GA13634@krava.brq.redhat.com> <20140911132911.GB10158@kernel.org> <20140911145945.GC32722@krava.brq.redhat.com> <20140911152330.GI10158@kernel.org> <20140911153527.GE32722@krava.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140911153527.GE32722@krava.brq.redhat.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Thu, Sep 11, 2014 at 05:35:27PM +0200, Jiri Olsa escreveu: > 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 I leave it as is now, when I add that void * pointer to each entry in fdarray->priv[], I will have to change fdarray's users, i.e. right now I will have to go and change evlist.h, i.e. every place that has: fda->priv[fd]; will have to be changed to: fda->priv[fd].idx; If I instead change it to: struct fdarray { ... union { int idx; } *priv; ... } Then I will not have to change anything when I add that void * pointer to the union. > > 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; > ... > } Yeah, that is what I am trying to avoid. This will make it use sizeof(void *) for each entry, and I have no use for that right now. All I need is sizeof(int) for each entry. Remember, this is an array, so its not just a matter of changing: int *priv; to: void *priv; But since it is an array, it will use, in this case, double the space, on 64-bit, for no gain _right now_. - Arnaldo