On 28-11-07 11:46, Robert P. J. Day wrote:
based on a book i'm reading, apparently i can write a loadable
module whose entire source file is nothing more than:
=====
#include <linux/module.h>
#include <linux/jiffies.h>
module_param(jiffies, uint, 444) ;
MODULE_LICENSE("Dual BSD/GPL");
=====
as you can see, its entire purpose is to make the internal value
"jiffies" available to me under /sys/module and, sure enough, using
the standard kbuild structure, it builds and loads and seems to work.
but i wasn't aware that you could write a valid loadable module
without at least a call to module_init(). in fact, from
include/linux/init.h:
/* Each module must use one module_init(), or one no_module_init */
clearly, i'm not doing that. so, should i have been surprised that
the above is a valid loadable module? why does it load without a call
to module_init() that returns a success value of zero?
Due to:
=== kernel/module.c
asmlinkage long sys_init_module(...)
{
[ ... ]
int ret = 0;
[ ... ]
/* Start the module */
if (mod->init != NULL)
ret = mod->init();
if (ret < 0) {
[ ... ]
}
/* Now it's a first class citizen! */
mutex_lock(&module_mutex);
[ ... ]
}
That is --- the above quoted comment is incorrect. A module can certainly do
without a module_init() function (mod->init == NULL).
(mod->init is set from the module struct in the .gnu.linkonce.this_module
section inside the module itself).
Rene.
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