lkmpg/examples/procfs4.c
2021-07-22 07:29:07 +08:00

142 lines
3.2 KiB
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 */
#include <linux/version.h>
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 6, 0)
#define HAVE_PROC_OPS
#endif
#define PROC_NAME "iter"
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
*
*/
#ifdef HAVE_PROC_OPS
static const struct proc_ops my_file_ops = {
.proc_open = my_open,
.proc_read = seq_read,
.proc_lseek = seq_lseek,
.proc_release = seq_release,
};
#else
static const struct file_operations my_file_ops = {
.open = my_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
};
#endif
/**
* This function is called when the module is loaded
*
*/
int init_module(void)
{
struct proc_dir_entry *entry;
entry = proc_create(PROC_NAME, 0, NULL, &my_file_ops);
if (entry == NULL) {
remove_proc_entry(PROC_NAME, NULL);
pr_debug("Error: Could not initialize /proc/%s\n", PROC_NAME);
return -ENOMEM;
}
return 0;
}
/**
* This function is called when the module is unloaded.
*
*/
void cleanup_module(void)
{
remove_proc_entry(PROC_NAME, NULL);
pr_debug("/proc/%s removed\n", PROC_NAME);
}