linux-kernel - Re: [PATCH v2] perf tools: New function to parse string representing size in bytes

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Message-Id: <20091115.185220.212229853.mitake@dcl.info.waseda.ac.jp>
Date:	Sun, 15 Nov 2009 18:52:20 +0900 (JST)
From:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	paulus@...ba.org, fweisbec@...il.com
Subject: Re: [PATCH v2] perf tools: New function to parse string
 representing size in bytes

From: Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v2] perf tools: New function to parse string representing size in bytes
Date: Sun, 15 Nov 2009 09:57:11 +0100

Thanks for your review, and sorry for my lots of fault...
I'll send version 3 later.

> * Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:
> 
> > This patch modifies util/string.[ch] to add new function: bytesexp2int()
> > to parse string representing size in bytes.
> > 
> > This is version 2. Acording to Frederic and Ingo's advice,
> > I removed static function digit() and rewrote to use
> > isdigit() macro of util.h.
> > 
> > Below is the description of bytesexp2int().
> > 
> > Parse (\d+)(b|B|kb|KB|mb|MB|gb|GB) (e.g. "256MB")
> > and return its numeric value. (e.g. 268435456)
> > 
> > The parameter str is not changed before and after calling,
> > but it changed temporally and internally for atoi().
> > So type of str is char *, not const char *.
> > 
> > Signed-off-by: Hitoshi Mitake <mitake@....info.waseda.ac.jp>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Cc: Paul Mackerras <paulus@...ba.org>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> >  tools/perf/util/string.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/string.h |    1 +
> >  2 files changed, 83 insertions(+), 0 deletions(-)
> 
> Please run checkpatch on patches in the future, for this patch it shows 
> this small problem:
> 
> ERROR: trailing whitespace
> #68: FILE: tools/perf/util/string.c:66:
> +^I$
> 
> > diff --git a/tools/perf/util/string.c b/tools/perf/util/string.c
> > index 04743d3..1ee7b17 100644
> > --- a/tools/perf/util/string.c
> > +++ b/tools/perf/util/string.c
> > @@ -1,4 +1,5 @@
> >  #include <string.h>
> > +#include <stdlib.h>
> >  #include "string.h"
> >  
> >  static int hex(char ch)
> > @@ -43,3 +44,84 @@ char *strxfrchar(char *s, char from, char to)
> >  
> >  	return s;
> >  }
> > +
> > +#define K 1024
> > +/*
> > + * bytesexp2int()
> > + * Parse (\d+)(b|B|kb|KB|mb|MB|gb|GB) (e.g. "256MB")
> > + * and return its numeric value
> > + *
> > + * The parameter str is not changed before and after calling,
> > + * but it changed temporally and internally for atoi().
> > + * So type of str is char *, not const char *.
> > + */
> > +int bytesexp2int(char *str)
> 
> why not to longlong?
> 
> > +{
> > +	int i, unit = 1;
> > +	char shelter = '\0';
> > +	size_t length = -1;
> > +
> > +	if (!isdigit(str[0]))
> > +		goto err;
> > +	
> > +	for (i = 1; i < (int)strlen(str); i++) {
> 
> This extra '(int)' cast should be eliminated. In the kernel we avoid 
> unnecessary casts - here i suspect it can be done by changing 'int i' to 
> 'unsigned int i'.
> 
> > +		switch (str[i]) {
> > +		case 'B':
> > +		case 'b':
> > +			break;
> > +		case 'K':
> > +			if (str[i + 1] != 'B')
> > +				goto err;
> > +			else
> > +				goto kilo;
> > +		case 'k':
> > +			if (str[i + 1] != 'b')
> > +				goto err;
> > +kilo:
> > +			unit = K;
> > +			break;
> > +		case 'M':
> > +			if (str[i + 1] != 'B')
> > +				goto err;
> > +			else
> > +				goto mega;
> > +		case 'm':
> > +			if (str[i + 1] != 'b')
> > +				goto err;
> > +mega:
> > +			unit = K * K;
> > +			break;
> > +		case 'G':
> > +			if (str[i + 1] != 'B')
> > +				goto err;
> > +			else
> > +				goto giga;
> > +		case 'g':
> > +			if (str[i + 1] != 'b')
> > +				goto err;
> > +giga:
> > +			unit = K * K * K;
> > +			break;
> > +		case '\0':	/* only specified figures */
> > +			unit = 1;
> > +			break;
> > +		default:
> > +			if (!isdigit(str[i]))
> > +				goto err;
> > +			break;
> 
> (Might want to add tera as well, just in case this gets librarized into 
> the rest of the kernel some day.)
> 
> > +		}
> > +	}
> > +
> > +	shelter = str[i];
> > +	str[i] = (char)'\0';
> 
> a spurious type cast again - they should really be avoided. Here it's 
> unnecessary, character literals should auto-convert to the proper type 
> just fine.
> 
> 
> > +	length = atoi(str) * unit;
> > +	if (shelter != '\0')
> > +		str[i] = shelter;
> > +
> > +	goto end;
> > +
> > +err:
> > +	length = -1;
> > +end:
> > +	return length;
> > +}
> 
> small naming nit, please use 'out_err:' and 'out:' labels. (which is how 
> we generally name such exception exit points)
> 
> 
> Thanks,
> 
> 	Ingo
> 
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