Hi all
I am Newbie to linux kernel but try to trace and understand it .
when I look at usb related code in linux kernel . I found one interesting macro in module.h as following .

#ifdef MODULE
#define MODULE_GENERIC_TABLE(gtype,name) \
extern const struct gtype##_id __mod_##gtype##_table \
__attribute__ ((unused, alias(__stringify(name))))

extern struct module __this_module;
#define THIS_MODULE (&__this_module)
#else /* !MODULE */
#define MODULE_GENERIC_TABLE(gtype,name)
#define THIS_MODULE ((struct module *)0)
#endif

if I define MODULE , I can find __this_module some where in ohci-hcd.mod.c or ehci-hcd.mod.c else .
my question is what ((struct module*)0) is if I do not define MODULE ?
have never seen ((struct module*)0) before . hard to image about it .
Thanks

Kevin ...

It is simply a null pointer. The cast is placed there so that the null will be forced to be a particular pointer type (in this case a pointer to struct module), so that there will be type checking at the point where THIS_MODULE is used.

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