linux-kernel - Re: [PATCH v2 14/14] perf tools: Move subcommand framework and related utils to libapi

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Date:	Wed, 9 Dec 2015 06:33:15 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Namhyung Kim <namhyung@...nel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 14/14] perf tools: Move subcommand framework and
 related utils to libapi

On Wed, Dec 09, 2015 at 09:03:43AM +0100, Ingo Molnar wrote:
> 
> * Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> > > > wouldn't necessarily be a clean split.  It would also possibly create more 
> > > > room for error for the users of libapi, since there would then be three 
> > > > config interfaces instead of one.
> > > 
> > > Humm, and now that you talk... libapi was supposed to be just sugar coating 
> > > kernel APIs, perhaps we need to put it somewhere else in tools/lib/ than in 
> > > tools/lib/api/?
> > 
> > Ah, I didn't realize libapi was a kernel API abstraction library.  Shall we put 
> > it in tools/lib/util instead?
> 
> Yay, naming discussion! ;-)

Oh boy! ;-)

> So if this is about abstracting out the (Git derived) command-line option parsing 
> UI and help system, 'util' sounds a bit too generic.
> 
> We could call it something like 'lib/cmdline', 'lib/options'?
> 
> The (old) argument against making too finegrained user-space libraries was that 
> shared libraries do have extra runtime costs - this thinking resulted in catch-all 
> super-libraries like libgtk:
> 
>   size /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
>      text    data     bss     dec     hex filename
>   7199789   57712   15128 7272629  6ef8b5 /usr/lib/x86_64-linux-gnu/libgtk-3.so.0
> 
> But in tools/ we typically link the libraries statically so there's no shared 
> library cost to worry about. (Build time linking is a good idea anyway, should we 
> ever want to make use of link-time optimizations. It also eliminates version skew 
> and library compatibility breakage.)
> 
> The other reason for the emergence of super-libraries was the high setup cost of 
> new libraries: it's a lot easier to add yet another unrelated API to libgtk than 
> to start up a whole new project and a new library. But this setup cost is very low 
> in tools/ - one of the advantage of shared repositories.
> 
> So I think in tools/lib/ we can continue to do a clean topical separation of 
> libraries, super-libraries are not needed.

I definitely agree that for the reasons you outlined, something like
'lib/cmdline' would be a good idea.  Except... there's a wrinkle, of
course.

The library also includes non-cmdline-related dependencies.  And these
dependencies are directly used by perf as well.  So if we name it
'cmdline', perf would have includes like:

#include <cmdline/pager.h>
#include <cmdline/strbuf.h>
#include <cmdline/term.h>
#include <cmdline/wrapper.h>
...etc...

So it would be using several functions from the 'cmdline' library which
are unrelated to 'cmdline'.

For that reason I would vote to name it 'lib/util'.  But I don't really
care, I'd be ok with 'lib/marshmallow' if that's what you guys wanted
:-)

Thoughts?

-- 
Josh
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