linux-kernel - Re: RFC: introduce struct ksymbol

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Message-Id: <1239776051.32241.17.camel@localhost>
Date:	Tue, 14 Apr 2009 23:14:11 -0700
From:	Joe Perches <joe@...ches.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: RFC: introduce struct ksymbol

On Wed, 2009-04-15 at 07:58 +0200, Ingo Molnar wrote:
> (Sam and Rusty Cc:-ed)
> > Perhaps a conversion from
> > 
> > "char str[KSYM_SYMBOL_LEN]"
> > to
> > "struct ksymbol sym"?
> > 
> > could be useful.
> > 
> > There are a few places that use a hard coded length of 128
> > instead of KSYM_SYMBOL_LENGTH that are also converted.
> > 
> > Compile tested only
> 
> Why not 'struct ksym'? That name is unused right now, it is shorter 
> and just as descriptive.

Either's ok with me.

> Downsides would be loss of awareness of stack footprint impact. A 
> plain struct is easy to slap on, and it's not immediately visible 
> that it carries 128 bytes of weight.

Stack footprint with KSYM_SYMBOL_LEN isn't very apparent.
KSYM_SYMBOL_LEN is more than 200.

 #define KSYM_NAME_LEN 128
 #define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + (KSYM_NAME_LEN - 1) + \
                         2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + 1)
 
> It might also be confusing in 
> terms of the nature of the interface - whether it's a pointery 
> object or not.

Specified type makes it hard to pass the wrong
sized buffer.

> Prior use:
>         char str[KSYM_SYMBOL_LEN];
>         kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> New use:
> 	struct ksym sym;
> 	kallsyms_lookup(rec->ip, NULL, NULL, NULL, &sym);

cheers, Joe

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