Procfs tutorial

Sample code for creating entries inside proc filesystem:

=======================================================================

/*

 * This Kernel module will create 3 proc entry, one parent directory and two

 * entries under this parent.

 */

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/proc_fs.h>

#include <asm/uaccess.h>

#define MODULE_NAME "Proc_entry_sample_module"

#define MAX_BUFFER_SIZE 1024

#define PROC_DIR_NAME "Hello_proc_dir"

static char procfs_buffer[MAX_BUFFER_SIZE];

static unsigned long procfs_buffer_size = 0;

static struct proc_dir_entry *dir , *file1 , *file2;

int hello_file_read (char *buffer, char ** buffer_location, off_t offset ,

                        int buffer_length ,int *eof ,  void *data )

{

int ret;

printk(KERN_INFO"\nReading /Procfs..");

if (offset > 0) {

ret = 0;

                *eof = 1;

} else {

memcpy (buffer,procfs_buffer,procfs_buffer_size);

ret=procfs_buffer_size;

}

printk (KERN_INFO"\nret = %d",ret);

return ret;

}

int hello_file_write(struct file *file , const char *buffer,

                                unsigned long count,void *data )

{

printk (KERN_INFO"\nWriting to /ProcFS..");

        printk("count=%d",count);

procfs_buffer_size = count;

if (procfs_buffer_size > MAX_BUFFER_SIZE) {

procfs_buffer_size = MAX_BUFFER_SIZE;

} else {

                procfs_buffer_size = count;

        }

if (copy_from_user (procfs_buffer,buffer,procfs_buffer_size))

return -EFAULT;

printk (KERN_INFO"\nret = %lu",procfs_buffer_size);

return procfs_buffer_size;

}

static int __init my_init_function(void)

{

int ret = 0;

dir = proc_mkdir (PROC_DIR_NAME,NULL);

if(dir == NULL) {

ret = -ENOMEM;

printk (KERN_ERR"\nDirectory creation failed");

                goto out_err;

        } else {

printk (KERN_INFO"\nDirectory created");

}

file1 = create_proc_entry ("file1",0644,dir);

if (file1 == NULL) {

ret = -ENOMEM;

printk ("\nfile1 creation failed");

                goto out_err;

} else {

printk(KERN_INFO"\nfile1 under dir created");

}

file1->read_proc=hello_file_read;

file1->write_proc=hello_file_write;

file1->mode=S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;

file2 = create_proc_entry ("file2",0644,dir);

        if (file2 == NULL) {

ret = -ENOMEM;

printk ("\nfile2 creation failed");

                goto out_err;

} else {

printk(KERN_INFO"\nfile2 under dir created");

}

file2->read_proc=hello_file_read;

        file2->write_proc=hello_file_write;

file2->mode=S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;

out:

return ret;

out_err:

        printk("\nModule failed to create proc entries !!");

        goto out;

}

static void __exit my_exit_function(void)

{

remove_proc_entry("file1",dir);

remove_proc_entry("file2",dir);

remove_proc_entry("dir",NULL);

printk(KERN_INFO"\nAll Proc entries of %s kernel module removed"

                                ,MODULE_NAME);

printk(KERN_INFO"\n%s module unregistered",MODULE_NAME);

}

module_init(my_init_function);

module_exit(my_exit_function);

MODULE_DESCRIPTION("Kernel module for handing procfs entires.");

MODULE_AUTHOR("Narendra Pal Singh");

MODULE_LICENSE("GPL");

========================================================================

Makefile:

obj-m += proc_example.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

========================================================================

Steps to run:

1.  #make
2.  #insmod proc_example.ko

3.  #cd /proc

You will a directory of name "Hello_proc_dir".

4. #cd Hello_proc_dir

now can you can fire echo / cat commands to these two proc files named "file1" and "file2"