linux-kernel - Re: what means "module_param(channel_mask, channel

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Message-Id: <1247316097.7262.11.camel@localhost.localdomain>
Date:	Sat, 11 Jul 2009 14:41:37 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	"Robert P. J. Day" <rpjday@...shcourse.ca>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: what means "module_param(channel_mask, channel_mask, 0644)"?

On Sat, 2009-07-11 at 07:01 -0400, Robert P. J. Day wrote:
> researching my next newbie column about module parameters and i ran
> across the following:
> 
> drivers/input/misc/ati_remote2.c:module_param(channel_mask, channel_mask, 0644);
> drivers/input/misc/ati_remote2.c:module_param(mode_mask, mode_mask, 0644);
> 
> i have no idea what it means to have the second (type) field of
> module_param() simply repeat the name of the parameter.  is this some
> strange magic?  those two names don't *appear* to be typedef'ed
> anywhere i can see.

See include/linux/moduleparam.h:
    /* Helper functions: type is byte, short, ushort, int, uint, long,
       ulong, charp, bool or invbool, or XXX if you define param_get_XXX,
       param_set_XXX and param_check_XXX. */
    #define module_param_named(name, value, type, perm)                        \
            param_check_##type(name, &(value));                                \
            module_param_call(name, param_set_##type, param_get_##type, &value, perm); \
            __MODULE_PARM_TYPE(name, #type)

    #define module_param(name, type, perm)                          \
            module_param_named(name, name, type, perm)

And in drivers/input/misc/ati_remote2.c we find:
    #define param_check_channel_mask(name, p) __param_check(name, p, unsigned in
    #define param_set_channel_mask ati_remote2_set_channel_mask
    #define param_get_channel_mask ati_remote2_get_channel_mask
    module_param(channel_mask, channel_mask, 0644);
    [...]
    #define param_check_mode_mask(name, p) __param_check(name, p, unsigned int)
    #define param_set_mode_mask ati_remote2_set_mode_mask
    #define param_get_mode_mask ati_remote2_get_mode_mask
    module_param(mode_mask, mode_mask, 0644);

To me that looks like two implementations of the three param_*_XXX
functions described in the comment quoted above.

Does that answer your question?

Regards,


Paul Bolle

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