linux-kernel - Re: [GIT PULL 00/21] perf/core improvements and fixes

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Message-ID: <20131210124658.GA31256@gmail.com>
Date:	Tue, 10 Dec 2013 13:46:58 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Ben Cheng <bccheng@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Dongsheng Yang <yangds.fnst@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung.kim@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT PULL 00/21] perf/core improvements and fixes


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Adrian Hunter <adrian.hunter@...el.com> wrote:
> 
> > -void dso__set_short_name(struct dso *dso, const char *name)
> > +void dso__set_short_name(struct dso *dso, const char *name, bool sname_alloc)
> >  {
> >  	if (name == NULL)
> >  		return;
> > +	if (dso->sname_alloc)
> > +		free((char *)dso->short_name);
> > +	dso->sname_alloc = sname_alloc;
> 
> Calling the function option the same as the field name is asking for 
> trouble - I'd suggest 'new_sname_alloc' for the parameter, or so.
> 
> And I'd also remove the 'const' from struct dso::short_name, it 
> probably does not help code generation, because 'dso' is passed in as 
> const in all the non-lifetime methods anyway.
> 
> That way the cast can be dropped from the free().
> 
> Similar problems exist with the usage of 'short_name' - it overloads 
> the field name which makes it somewhat confusing, and it's also 
> sometimes inconsistently named, such as 'name' in 
> dso__set_short_name().
> 
> Ditto for 'long_name' handling.
> 
> Also, the 'sname_alloc' name sucks, it does not make it obvious that 
> it's related to 'short_name', hiding its true significance (and hiding 
> the broken life time handling of the flag/pointer combo). I'd rename 
> it to something more descriptive, like ->short_name_allocated - or I'd 
> rename everything to 'sname'/'lname' naming for short/long names.
> 
> Every time one runs into a crash like this it's a canary signal that 
> cleanliness principles need hardening.

More observations about util/dso.c:

 - dso__binary_type_file() should probably pass in 'const struct dso'

 - dso__binary_type_file()'s filename string parameter should be named 
   'filename', not 'file' ...

 - build_id__sprintf() looks fragile: every single use of it appears 
   to follow this pattern:

	build_id__sprintf(x, sizeof(x), ...)

   this could be simplified (and eliminating the possibility to typo a 
   bug) by changing the function to __build_id__snprintf() and adding 
   a build_id__sprintf() wrapper macro around it:

	build_id__sprintf(x, ...)

   that generates the size itself.

 - dso__binary_type_file() is a method without a verb, so it's unclear 
   what it does. It probably wants to be renamed to 
   dso__set_binary_type_file() or so?

 - dso_cache__find() probably wants to pass in a const rb_root.

 - 'struct dso *pos' should probably be named 'struct dso *dso_pos' or 
   so - 'pos' is frequently used for integer variable names so its use 
   for an object iterator feels confusing.

 - the 'head' argument of dsos__find() wants to be constified too I 
   guess

Thanks,

	Ingo
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