linux-kernel - Re: [PATCH 1/2] Define find_symbol_in_section

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Date:	Wed, 15 Jul 2015 10:11:12 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	akpm@...ux-foundation.org, rob.jones@...ethink.co.uk,
	namhyung@...nel.org, linux-kernel@...r.kernel.org,
	Minfei Huang <mnfhuang@...il.com>
Subject: Re: [PATCH 1/2] Define find_symbol_in_section_t as function type to
 simplify the code

On 07/15/15 at 07:22am, Rusty Russell wrote:
> Minfei Huang <mhuang@...hat.com> writes:
> > From: Minfei Huang <mnfhuang@...il.com>
> >
> > It is not elegance, if we use function directly as the argument, like
> > following:
> >
> > bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
> >                                    struct module *owner,
> >                                    void *data), void *data);
> >
> > Here introduce a type defined function find_symbol_in_section_t. Now
> > we can use these type defined function directly, if we want to pass
> > the function as the argument.
> >
> > bool each_symbol_section(find_symbol_in_section_t fn, void *data);
> 
> I disagree.
> 
> It's shorter, but it's less clear.  typedefs on functions are not very
> useful:
> 1) They require readers to look in two places to see how to use the
>    function (ie each_symbol_section).
> 2) They can't use the typedef to declare their function, since that
>    doesn't work in C.
> 
> If the function were being used many times, it makes sense.  But
> it's only used twice, once static inside module.c.
> 
> So I won't be applying these.
> 
> Cheers,
> Rusty.
> 

Hi, Rusty.

The main reason why I posted these patch is the function has too much
parameters which may be confused with readers at the first glance. 

So it is better define a typedef function, although the readers shall
dig out what find_symbol_in_section_t is.

Thanks
Minfei

> > Signed-off-by: Minfei Huang <mnfhuang@...il.com>
> > ---
> >  include/linux/module.h | 6 +++---
> >  kernel/module.c        | 9 ++-------
> >  2 files changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index d67b193..1e125b1 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -462,14 +462,14 @@ const struct kernel_symbol *find_symbol(const char *name,
> >  					bool gplok,
> >  					bool warn);
> >  
> > +typedef bool (*find_symbol_in_section_t)(const struct symsearch *arr,
> > +		struct module *owner, void *data);
> >  /*
> >   * Walk the exported symbol table
> >   *
> >   * Must be called with module_mutex held or preemption disabled.
> >   */
> > -bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
> > -				    struct module *owner,
> > -				    void *data), void *data);
> > +bool each_symbol_section(find_symbol_in_section_t fn, void *data);
> >  
> >  /* Returns 0 and fills in value, defined and namebuf, or -ERANGE if
> >     symnum out of range. */
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 4d2b82e..1400c0b 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -426,9 +426,7 @@ extern const unsigned long __start___kcrctab_unused_gpl[];
> >  static bool each_symbol_in_section(const struct symsearch *arr,
> >  				   unsigned int arrsize,
> >  				   struct module *owner,
> > -				   bool (*fn)(const struct symsearch *syms,
> > -					      struct module *owner,
> > -					      void *data),
> > +				   find_symbol_in_section_t fn,
> >  				   void *data)
> >  {
> >  	unsigned int j;
> > @@ -442,10 +440,7 @@ static bool each_symbol_in_section(const struct symsearch *arr,
> >  }
> >  
> >  /* Returns true as soon as fn returns true, otherwise false. */
> > -bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
> > -				    struct module *owner,
> > -				    void *data),
> > -			 void *data)
> > +bool each_symbol_section(find_symbol_in_section_t fn, void *data)
> >  {
> >  	struct module *mod;
> >  	static const struct symsearch arr[] = {
> > -- 
> > 2.2.2
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