//kernel module: seqfile_exam.c
#include <linux/config.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/percpu.h>
#include <linux/sched.h>

static struct proc_dir_entry *entry;

static void *l_start(struct seq_file *m, loff_t * pos)
{
        loff_t index = *pos;

        if (index == 0) {
                seq_printf(m, "Current all the processes in system:\n"
                           "%-24s%-5s\n", "name", "pid");
                return &init_task;
        }
        else {
                return NULL;
        }
}

static void *l_next(struct seq_file *m, void *p, loff_t * pos)
{
        task_t * task = (task_t *)p;

        task = next_task(task);
        if ((*pos != 0) && (task == &init_task)) {
                return NULL;
        }
        ++*pos;
        return task;
}

static void l_stop(struct seq_file *m, void *p)
{
}

static int l_show(struct seq_file *m, void *p)
{
        task_t * task = (task_t *)p;

        seq_printf(m, "%-24s%-5d\n", task->comm, task->pid);
        return 0;
}

static struct seq_operations exam_seq_op = {
        .start = l_start,
        .next  = l_next,
        .stop  = l_stop,
        .show  = l_show
};

static int exam_seq_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &exam_seq_op);
}

static struct file_operations exam_seq_fops = {
        .open = exam_seq_open,
        .read = seq_read,
        .llseek = seq_lseek,
        .release = seq_release,
};

static int __init exam_seq_init(void)
{

        entry = create_proc_entry("exam_esq_file", 0, NULL);
        if (entry)
                entry->proc_fops = &exam_seq_fops;

        return 0;
}

static void __exit exam_seq_exit(void)
{
        remove_proc_entry("exam_esq_file", NULL);
}

module_init(exam_seq_init);
module_exit(exam_seq_exit);
MODULE_LICENSE("GPL");