linux-kernel - Re: [PATCH v3 14/17] perf: Remove subcmd dependencies on strbuf

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Date:	Mon, 14 Dec 2015 10:05:37 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v3 14/17] perf: Remove subcmd dependencies on strbuf

On Mon, Dec 14, 2015 at 12:44:21PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sun, Dec 13, 2015 at 10:18:14PM -0600, Josh Poimboeuf escreveu:
> > Introduce and use new astrcat() and astrcatf() functions which replace
> > the strbuf functionality for subcmd.
> 
> <SNIP>
>  
> > diff --git a/tools/perf/util/subcmd-util.h b/tools/perf/util/subcmd-util.h
> > new file mode 100644
> > index 0000000..98fb9f9
> > --- /dev/null
> > +++ b/tools/perf/util/subcmd-util.h
> > @@ -0,0 +1,24 @@
> > +#ifndef __PERF_SUBCMD_UTIL_H
> > +#define __PERF_SUBCMD_UTIL_H
> > +
> > +#include <stdio.h>
> > +
> > +#define astrcatf(out, fmt, ...)						\
> > +({									\
> > +	char *tmp = *(out);						\
> > +	if (asprintf((out), "%s" fmt, tmp ?: "", ## __VA_ARGS__) == -1)	\
> > +		die("asprintf failed");					\
> > +	free(tmp);							\
> > +})
> 
> Hey, don't add die() calls, please.
> 
> > +
> > +static inline void astrcat(char **out, const char *add)
> > +{
> > +	char *tmp = *out;
> > +
> > +	if (asprintf(out, "%s%s", tmp ?: "", add) == -1)
> > +		die("asprintf failed");
> > +
> > +	free(tmp);
> 
> Ditto.

This replaces strbuf, which also calls die() when allocations fail.  So
this duplicates the existing die-on-allocation-error functionality and
is nothing "new" from my perspective.

Do you want me to change all the callers (and callers' callers, etc) of
these functions to check for errors?

> And I think that this should go into tools/include/string.h and
> tools/lib/string.c, no?

If these functions simply duplicate some of strbuf's functionality and
they aren't used outside of libsubcmd then I don't see any reason to do
that.

> We should try to look at the kernel and try to follow naming, semantics,
> etc as much as possible. The kernel doesn't have a astrcat, just
> kasprintf() (that is in linux/kernel.h, perhaps because in userland
> asprintf is in stdio.h, not in string.h) , wonder how something like
> astrcat is done there... Doing some research now.

Ok.

-- 
Josh
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