我可以在可加载内核模块（外部库除外）中使用哪些头文件和函数？

Question

Section 2 of the Linux man pages contains system calls .

http://linux.die.net/man/2/

After finding this link, I say "OK! I use this reference for developing every modules, It is complete".

But it seems I can not use some functions of this section (like bind(2) ). After including required headers (like <sys/socket.h> ) the module compilation failed.

Some functions/macros like printk does not listed in the section 2. Many people used Linux Apis that I could not find any official reference for it (just like printk ). I don't know how they found these functions? (May be by reading whole source code of kernel instead of reading any reference)

Some functions like memset describes in section 3 (user space libraries) but kernel module developer can use it without any error!

Where I can found a COMPLETE reference of available headers and functions when developing a loadable kernel modules? (Something like MSDN and WINDDK references)

#include <linux/init.h>
#include <linux/module.h>

/* A complete list of availabe headers and functions is missing! */

static int my_init(void)
{
    return  0;
}

static void my_exit(void)
{
    return;
}

module_init(my_init);
module_exit(my_exit);

Answer 1

As you know, the Kernel is quite a big, big and independent beast. This means that you cannot include anything which is not found under your kernel source tree.

When you're implementing your module, that means the only things you can link to is what you got in :

• The kernel source tree itself
• Another module you've made (I would recommend to avoid this scenario though whenever possible ... )

Note that you will be able to use the functions only if they are exported. You can check this using the nm utility on the compiled .ko file of a module. If you want to export some symbols of your module, you have to use the macro EXPORT_SYMBOL .

Be careful not to confuse user-space includes, usually found under /usr/include with the kernel module headers (which you are likely wanting to link against).

In the example you gave, the sys/socket.h is the location of the header after a make headers_install . At this location, it is meant to be used by userspace applications. This is NOT what you want when you are programming a module.

I think you have to look deeper in the use of sockets in the kernel. By googling up a little, I found -> this <- on LWN and checked the include/linux/net.h header of my 3.8 kernel source tree. The patch described in the link is integrated in the kernel and is likely to be what you are looking for.

The memset example is also an illustration of what I explained this far : if you want to use it in a common application, you'll have to include the string.h header, which is simply located at /usr/include/string.h . Its kernel equivalent is found under ...

/your-kernel-source-tree-dir/include/linux/string.h

Et voila ! You can use memset and friends inside any piece of kernel code, as long as you include the right header !

Thus, when you feel some frustration, thinking Man, I was able to use this by simply including this header in my apps ... Take a deep look at the kernel source tree (or have grep do it for you ;) ). You are very likely to find what you are looking for !

Answer 2

As per my knowledge there is no such complete reference for kernel module programming. I suggest you study the LDD3 basic sections and http://www.tldp.org/LDP/lkmpg/2.6/html/lkmpg.html#AEN978 for a beginner.