exchange data from kernel to process

[AlexSuperTramp13]

Hi everybody,

I really am a newbie in kernel development and I have this question.

I am developing an application that need to read some informations from the kernel. More specifically these informations regard the TCP part of the kernel.

I thought I could use the /proc filesystem in order to make the kernel write those informations in a specific file.

But until now I didn't find a complete guide that explains how to do this.

In any guide (I can't post URLs), for example, it is said that we need to create a module and when the module is loaded the function create_proc_entry() will be called.

The problem is that the part of kernel which need to write my informations, is a static part, so I don't need to create that module.
But in that case, who will call the create_proc_entry? And where do I put all the functions mentioned in the guide then?
Can you please clarify this to me?

Thanks,

Riccardo

[barunparichha]

I have written a simple driver to write content to some user space file.
Please change this as per your need.

/*
*Module.c
*/
#include <linux/module.h>  // Needed by all modules
#include <linux/kernel.h>  // Needed for KERN_INFO
#include <linux/fs.h>      // Needed by filp
#include <linux/string.h>
#include <asm/uaccess.h>   // Needed by segment descriptors

int init_module(void)
{
// Create variables
        struct file *f;
        char buf[128];
        mm_segment_t fs;
        int i;

// Init the buffer
        for(i=0;i<128;i++)
                buf[i] = 0;

        printk(KERN_INFO "My module is loaded\n");

//Open the file
        f = filp_open("/etc/testFile", O_CREAT|O_WRONLY|O_APPEND, 0);
        if(f == NULL)
                printk(KERN_ALERT "filp_open error!!.\n");
        else
        {
                // Get current segment descriptor
                fs = get_fs();
                // Set segment descriptor associated to kernel space
                set_fs(get_ds());

// Write to buf
strcpy(buf,"I love my country");

// Write to the file
                f->f_op->write(f, buf, strlen(buf), &f->f_pos);
                // Restore segment descriptor
                set_fs(fs);
        }

//close the file
        filp_close(f,NULL);
        return 0;
}

void cleanup_module(void)
{
            printk(KERN_INFO "My module is unloaded, so now check your new file content\n");
}

Your Makefile

obj-m += module.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Let me know for any issue.
Regards,
Barun Parichha

[AlexSuperTramp13]

Hi barunparichha,

I have solved my problem now, because I modified an already existing proc file, instead of creating a new one.

Still your module is very useful and rather simple to understand, so I am sure it will come in handy sooner or later.

Thank you,

Riccardo