Message-ID: <20151210151536.GF29872@treble.redhat.com>
Date:	Thu, 10 Dec 2015 09:15:36 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...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 Thu, Dec 10, 2015 at 09:55:53AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Dec 09, 2015 at 12:59:15PM -0600, Josh Poimboeuf escreveu:
> > On Wed, Dec 09, 2015 at 12:58:08PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Wed, Dec 09, 2015 at 06:33:15AM -0600, Josh Poimboeuf escreveu:
> > > > 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
> > > > :-)
> > > 
> > > Right, now you see why this wasn't librarised before, huh? Untangling
> > > bits in a way that this gets sane takes a bit of time.
> > > 
> > > I'm going thru your patchkit to erode it a bit, taking uncontroversial
> > > patches.
> > > 
> > > I also would just do one thing first, i.e. just move the cmdline parts
> > > to lib/cmdline/, then we would look at the rest. I.e. reduce the problem
> > > first.
> > > 
> > > Yeah, I haven't looked deeply how difficult that would be :-\
> > 
> > Ok.  I've taken a deeper look at how we could just have a 'cmdline'
> > library without the extra unrelated utils.
> > 
> > (BTW, I actually think a name like 'subcmd' would be a better fit than
> > 'cmdline'.  Because it deals not only with the cmdline, but more
> > specifically with subcommands, as well as the exec'ing of external
> > subcommands and other subprograms.  And any program that wants to have a
> > "perf"- or "git"-like "subcommand" interface would use it, thus 'subcmd'
> > is a more natural fit.)
> 
> Ack, see? We'd eventually get to some better name than "util" :-)

Yes, this is much better than both 'libutil' and 'libmarshmallow' ;-)

> > I looked at the files which are unrelated to subcommands and which are
> > used by both the subcmd code and perf:
> > 
> > - abspath.c: needed by exec_cmd.c for the make_nonrelative_path()
> >   function, but it's a small function which can just be duplicated by
> >   copying it into exec_cmd.c.
> 
> ack
>    
> > - ctype.c: used by parse-options.c for tolower(), but it's not strictly
> >   necessary; instead the glibc version of tolower() can be used.
> 
> ack
>  
> > - pager.c: this isn't directly 'cmdline' related, but does fit the theme
> >   of 'subcmd', since it pipes a child process to 'less'.  So it could
> >   reasonably live in the library.
> 
> ack
>  
> > - strbuf.c: used sparingly by parse-options.c, exec_cmd.c, and help.c.
> >   I think all the uses can be replaced rather easily with calls to
> >   sprintf() and similar glibc string functions.
> 
> go for it, use asprintf, probably is all that is needed, it will
> allocate and format, extending would be just using existing stuff plus
> new call to asprintf.
>  
> >   (Another option would be to duplicate the ~150 lines of strbuf.c
> >   inside the library.  That would require renaming all the functions and
> >   structs in order to avoid duplicate symbol errors when linking with
> >   perf.)
> > 
> > - term.c: used by help.c for the get_term_dimensions() function, which
> >   is a small function which can be duplicated in help.c.
> > 
> > - usage.c: used in several places for die() and error(), but these are
> >   trivial functions which can be duplicated.
> > 
> > - wrapper.c: used in a few places for ALLOC_GROW() and xrealloc(), but
> >   ALLOC_GROW() can be duplicated locally and xrealloc() can be replaced
> >   by the use of realloc().
> > 
> > So in summary, with a small amount of code duplication, and a little
> > rewrite of the strbuf usage, I think I can extract a libsubcmd rather
> > cleanly.
> > 
> > How does that sound?
> 
> Just fine, proceed :-)
> 
> - Arnaldo

Thanks!  Working on v3 now.

-- 
Josh
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