kernel module development problem

[jphoenix]

Hi,

I am writing a simple kernel module which is to open() a file, read() some information from it, and close() it. As far as I know, all three of these functions are system calls and are provided by the kernel. Compiler warns me:
"sdlm.c:10: warning: implicit declaration of function `open'
sdlm.c:14: warning: implicit declaration of function `read'
sdlm.c:16: warning: implicit declaration of function `close'",
but builds the .ko module.

When sdlm.ko is inserted, an error occurs:
sdlm: Unknown symbol read
sdlm: Unknown symbol open
sdlm: Unknown symbol close

Please help me, what's the problem?


here is my code:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/unistd.h>
#include <linux/fcntl.h>

int     init_module()
{
    int fd;
    printk(KERN_INFO "SDL start");

    fd = open("/var/license.dat", O_RDWR, S_IRWXU);
    if (fd != -1)
    {
        char banner[200] = "";
        read(fd, banner, 199);
        printk(KERN_NOTICE "License data: `%s`", banner);
        close(fd);
    }
    else
        printk(KERN_NOTICE "License file not found");

    return 0;
}

void    cleanup_module()
{
    printk(KERN_INFO "SDL exit");
}

[gerard4143]

You can't use C library functions in the kernel.
Also this should be posted int the kernel section of this forum.

[jphoenix]

but those functions are not library functions, they are system calls and they are defined in <linux/unistd.h> file in kernel sources

OK then, one more question, how can I manage with files from kernel space?

[gerard4143]

I posted a very similar question in this forum under the kernel section. The posting is called "Writing to a file from a kernel module???". You should check it out...Hope this helps...Gerard4143

[jphoenix]

thank you Gerard, but I still believe this is possible...

[gerard4143]

Of course its possible...but is it worth the effort to hack this functionality into the kernel. With that said, if you do find a solution post it I'd like to see it...Geard4143