linux-kernel/debugfs/debugfs-example.c

   1 /*
   2  * Debugfs example module.
   3  *
   4  * Mount debugfs with:
   5  *
   6  * # mount -t debugfs debugfs /proc/sys/debugfs
   7  *
   8  * After loading this module, a directory called 'debugfs-example'
   9  * will be created under debugfs root dir and it will have two
  10  * files in it.
  11  *
  12  * One file is called 'stats_file' and it's an example of file
  13  * handling with debugfs. The other file is called 'statfs_u32'
  14  * and its an example of integer handling.
  15  *
  16  * Both files shows the contents of the stats_counter variable.
  17  *
  18  * Luiz Fernando N. Capitulino
  19  * <lcapitulino@gmail.com>
  20  */
  21 #include <linux/init.h>
  22 #include <linux/module.h>
  23 #include <linux/debugfs.h>
  24
  25 static struct dentry *root_dir, *dentry_stats, *dentry_u32;
  26 static u32 stats_counter;
  27
  28 static int stats_open(struct inode *inode, struct file *file)
  29 {
  30         ++stats_counter;
  31         return 0;
  32 }
  33
  34 #define TMPBUFSIZE 12 // random value
  35
  36 static ssize_t stats_read(struct file *file, char __user *buf, size_t nbytes,
  37                           loff_t *ppos)
  38 {
  39         size_t maxlen;
  40         char tmpbuf[TMPBUFSIZE];
  41
  42         maxlen = snprintf(tmpbuf, TMPBUFSIZE, "stats: %u\n", stats_counter);
  43         if (maxlen > TMPBUFSIZE)
  44                 maxlen = TMPBUFSIZE;
  45
  46         return simple_read_from_buffer(buf, nbytes, ppos, tmpbuf, maxlen);
  47 }
  48
  49 static const struct file_operations stats_operations = {
  50         .owner   = THIS_MODULE,
  51         .open    = stats_open,
  52         .read    = stats_read,
  53 };
  54
  55 static int __init debugfs_example_init(void)
  56 {
  57         root_dir = debugfs_create_dir("debugfs-example", NULL);
  58         if (!root_dir) {
  59                 printk(KERN_ERR "Could not create main directory\n");
  60                 return -ENOMEM;
  61         }
  62
  63         dentry_stats = debugfs_create_file("stats_file",
  64                                            S_IFREG|S_IRUGO|S_IWUSR,
  65                                            root_dir, NULL, &stats_operations);
  66         if (!dentry_stats) {
  67                 printk(KERN_ERR "ERROR: could not create stats_file\n");
  68                 debugfs_remove(root_dir);
  69                 return -ENOMEM;
  70         }
  71
  72         dentry_u32 = debugfs_create_u32("stats_u32",
  73                                         S_IFREG|S_IRUGO|S_IWUSR,
  74                                         root_dir, &stats_counter);
  75         if (!dentry_u32) {
  76                 printk(KERN_ERR "ERROR: could not create stats_u32");
  77                 debugfs_remove(dentry_stats);
  78                 debugfs_remove(root_dir);
  79                 return -ENOMEM;
  80         }
  81
  82         return 0;
  83 }
  84
  85 static void __exit debugfs_example_exit(void)
  86 {
  87         debugfs_remove(dentry_stats);
  88         debugfs_remove(dentry_u32);
  89         debugfs_remove(root_dir);
  90 }
  91
  92 module_init(debugfs_example_init);
  93 module_exit(debugfs_example_exit);
  94
  95 MODULE_LICENSE("GPL");
  96 MODULE_DESCRIPTION("A debugfs example module");
  97 MODULE_AUTHOR("Luiz Capitulino <lcapitulino@gmail.com>");