how to export function from fs/dropcache.c

[er krishna]

Dear All,



 I have one  simple problem in exporting the function. Everything is fine,
but its not working as per the expectation.  Actually I have to export some
function from fs/dropcache.c, but it is not working as per the expectataion,
[ I am able to export any function from other files like fs/buffer.c and
block/genhd.c but dropcache.c creates a problem] .I am attaching the file.
Just once check & please tell if something is missing, what I have done is
as follows:



I have exported three functions from fs/dropcaches.c by making their
function declaration in linux/mm.h, compiled the  corresponding 2.6.26
kernel & got their entries in System.map file as follows:


c0174d98 T drop_slab
c0174db2 T drop_pagecache
c0174ea7 T drop_caches_sysctl_handler

These entries are quite different from the actual exported functions from
other files, it has only T option. Can antbody elaborate what is the meaning
of these options  like T, t, r , u and so on?

I have booted with same 2.6.26 kernel.  I included linux/mm.h  and all the
above three function in my module done make & found following warnings in
compilation & following error message in insmod due to some linking error:


[r...@centos2 kernel]# make
make -C /lib/modules/2.6.26/build M=/root/kernel modules
make[1]: Entering directory `/root/Desktop/linux-2.6.26'
  Building modules, stage 2.
  MODPOST 2 modules
WARNING: "drop_slab" [/root/kernel/dropcache.ko] undefined!
WARNING: "drop_pagecache" [/root/kernel/dropcache.ko] undefined!
WARNING: "drop_caches_sysctl_handler" [/root/kernel/dropcache.ko] undefined!
make[1]: Leaving directory `/root/Desktop/linux-2.6.26'
[r...@centos2 kernel]#
[r...@centos2 kernel]#
[r...@centos2 kernel]# insmod dropcache.ko
insmod: error inserting 'dropcache.ko': -1 Unknown symbol in module
[r...@centos2 kernel]#
[r...@centos2 kernel]#


Any idea how to trace it & what is missing, as I got all the exported
entries in System.map file & I have included the function declaration file
linux/mm.h on the same compiled kernel, it should do the things in right
manner.

Please suggest, If I am missing something or you want any more information.
I am attaching my kernel module and these are some more snippet :
[r...@centos2 kernel]# uname -a
Linux CENTOS2 2.6.26 #1 SMP Sun Jul 19 10:54:05 IST 2009 i686 i686 i386
GNU/Linux
[r...@centos2 kernel]#
[r...@centos2 kernel]# tail -1 /root/Desktop/linux-2.6.26/fs/drop_caches.c
EXPORT_SYMBOL(drop_caches_sysctl_handler);
[r...@centos2 kernel]#
[r...@centos2 kernel]#








Thanks and Best Regards,
------------------------
Krishna Kumar

#include <linux/module.h>      
#include <linux/kernel.h>
#include<linux/kmod.h>
#include<linux/mm.h>
#include<linux/fs.h>
#include<linux/writeback.h>
#include<linux/sysctl.h>
#include<linux/gfp.h>
int init_module(void)
{
printk(KERN_INFO   " trying to check the exported function calling : drop_caches_sysctl_handler,drop_pagecache and drop_slab\n");	
//drop_caches_sysctl_handler(ctl_table *table, int write, struct file *, v	oid __user *buffer, size_t *length, loff_t *ppos);
drop_caches_sysctl_handler(NULL, 0, NULL, NULL, NULL, NULL);
drop_pagecache();
drop_slab();
return 0;
}

void cleanup_module(void)
{
printk(KERN_INFO "outside drop_cache_sysctl_handler");
}