Re: RFC: introduce struct ksymbol

[Joe Perches <joe@perches.com>]

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