undefined reference

The case is quite complicated.

I am now developing a module. This module need communicate with the kernel. So I exported a function func(), by using EXPORT_SYMBOL(func). In the header file, I set "extern int func()".

I also modified the kernel source code, which is inode.c, and insert the func() and the module header file.

After the above procedure, I use "make bzImage" to build the kernel. At the compile stage, it does not appear warning message, but it appears in the linking object stage, which is

fs/fs.o(.text+0x1377d): undefined reference to `func'

How can I solve this issue? Or any parameter for "ld" to avoid checking the undefined reference?
Thanks.

<snip>

The problem you face is that the kernel needs to know where foo is to generate a the bytecode that calls it. Here is a better scenario...

You expose an interface in the kernel such as

	typedef void (*func_t)(int);
	void register_func ( func_t func );
	EXPORT_SYMBOL (register_func);

Then in your modules you call 'register_func' and that will pass the function in question to the kernel. The kernel can then do whatever it wants to that pointer (like call it).

B.

				WebSig: http://www.jukie.net/~bart/sig/

Or let me say clearly.

The suitution is I want the kernel source use the symbol from module.

What I did in the module code are:
1. EXPORT_SYMBOL(func) in the source code of module
2. Set "extern int func()" in the module header

What I did in the kernel source code are:
1. Insert "func()" in the inode.c
2. Add the module header in the kernel source code

Then I use "make bzImage", I got no error message on compiling inode.c, but I got

"fs/fs.o(.text+0x1377d): undefined reference to `func'"

in the linking stage.

I also set condition inode.c to check the existing of module before calling func()

Thanks

Regards,
Anthony

----- Original Message -----
From: "Bart Trojanowski" <[email protected]>
To: "Anthony Chee" <[email protected]>; <[email protected]>
Cc: <[email protected]>; <[email protected]>; <[email protected]>
Sent: Tuesday, March 26, 2002 5:45 AM
Subject: Re: undefined reference

You cannot do that. The kernel must be self contained. The only way for the kernel to access module code and data is for the module to register that code and data when the module is loaded and for the kernel to access the module via the registration list.

See any module that handles a filesystem. sys_open() does not call the module directly. A module registers its file operations on load. The kernel (dentry_open) calls the module via f->f_op->open.

but

Thanks for your help. I use another apporach to communicate with module, similiar to the method you stated above.

What I did in the kernel source,

1. In fs.h, I added one line in struct super_operations

            int (*query_module) (struct inode *);

2. In write_inode() of inode.c, added

            result = inode->i_sb->s_op->query_module(inode);

What I did in the module,

1. Build up my own function, kernel_query_module(struct inode *inode)

2. In init_module(), added
struct super_block *sb_ptr;
sb_ptr = get_super(MKDEV(8,1)); /* suppose I want to
get super_block of /dev/sda1 */

            sb_ptr -> s_op -> query_module = &kernel_query_module;

Then, I compile the module and didi not get error message When I compile the kernel, I got the follow error message,

inode.c:195: structure has no member named `query_module'

It made me crazy. Why the module can access the s_op and register the address of kernel_query_module, but not the kernel source? I already added one more item in the struct super_operation, but got the error message the struct has no such member.

Any thing I missed? Thanks.