procfs4.c
/**
 * procfs4.c - create a "file" in /proc
 *      This program uses the seq_file library to manage the /proc file.
 *
 */
#include <linux/kernel.h>       /* We're doing kernel work */
#include <linux/module.h>       /* Specifically, a module */
#include <linux/proc_fs.h>      /* Necessary because we use proc fs */
#include <linux/seq_file.h>     /* for seq_file */
 
#define PROC_NAME       "iter"
MODULE_AUTHOR("Philippe Reynes");
MODULE_LICENSE("GPL");
 
/**
 * This function is called at the beginning of a sequence.
 * ie, when:
 *      - the /proc file is read (first time)
 *      - after the function stop (end of sequence)
 *
 */
static void *my_seq_start(struct seq_file *s, loff_t *pos)
{
  static unsigned long counter = 0;
  /* beginning a new sequence ? */
  if ( *pos == 0 )
    {
      /* yes => return a non null value to begin the sequence */
      return &counter;
    }
  else
    {
      /* no => it's the end of the sequence, return end to stop reading */
      *pos = 0;
      return NULL;
    }
}
 
/**
 * This function is called after the beginning of a sequence.
 * It's called untill the return is NULL (this ends the sequence).
 *
 */
static void *my_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
  unsigned long *tmp_v = (unsigned long *)v;
  (*tmp_v)++;
  (*pos)++;
  return NULL;
}
 
/**
 * This function is called at the end of a sequence
 *
 */
static void my_seq_stop(struct seq_file *s, void *v)
{
  /* nothing to do, we use a static value in start() */
}
 
/**
 * This function is called for each "step" of a sequence
 *
 */
static int my_seq_show(struct seq_file *s, void *v)
{
  loff_t *spos = (loff_t *) v;
  seq_printf(s, "%Ld\n", *spos);
  return 0;
}
 
/**
 * This structure gather "function" to manage the sequence
 *
 */
static struct seq_operations my_seq_ops = {
  .start = my_seq_start,
  .next = my_seq_next,
  .stop = my_seq_stop,
  .show = my_seq_show
};
 
/**
 * This function is called when the /proc file is open.
 *
 */
static int my_open(struct inode *inode, struct file *file)
{
  return seq_open(file, &my_seq_ops);
};
 
/**
 * This structure gather "function" that manage the /proc file
 *
 */
static struct file_operations my_file_ops = {
  .owner    = THIS_MODULE,
  .open     = my_open,
  .read     = seq_read,
  .llseek = seq_lseek,
  .release = seq_release
};
 
/**
 * This function is called when the module is loaded
 *
 */
int init_module(void)
{
  struct proc_dir_entry *entry;
  entry = create_proc_entry(PROC_NAME, 0, NULL);
  if (entry) {
    entry->proc_fops = &my_file_ops;
  }
  return 0;
}
 
/**
 * This function is called when the module is unloaded.
 *
 */
void cleanup_module(void)
{
  remove_proc_entry(PROC_NAME, NULL);
}
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