c/lkm/proc.c

   1 /* Standard includes for modules */
   2 #include <linux/kernel.h>
   3 #include <linux/module.h>
   4 #include <linux/init.h>
   5
   6 /* for proc_dir_entry and create_proc_entry */
   7 #include <linux/proc_fs.h>
   8
   9 /* For sprintf and snprintf */
  10 #include <linux/string.h>
  11
  12 /* For copy_from_user */
  13 #include <linux/uaccess.h>
  14
  15 MODULE_LICENSE("GPL");
  16 MODULE_AUTHOR("Ormi <ormi.ormi@gmail.com>");
  17 MODULE_DESCRIPTION("Simple module using procfs");
  18
  19 static char our_buf[256];
  20
  21 int buf_read(char *buf, char **start, off_t offset, int count, int *eof, void *data)
  22 {
  23         int len;
  24         /* For example - when content of our_buf is "hello" - when user executes command "cat /proc/test_proc"
  25         he will see content of our_buf(in our example "hello" */
  26         len = snprintf(buf, count, "%s", our_buf);
  27         return len;
  28 }
  29
  30 /* When user writes to our entry. For example "echo "aa" > /proc/test_ptoc". "aa" will be stored in our_buf.
  31 Then, when user reads from our entry(cat /proc/test_proc) he will see "aa" */
  32 static int buf_write(struct file *file, const char *buf, unsigned long count, void *data)
  33 {
  34         /* If count is bigger than 255, data which user wants to write is too big to fit in our_buf. We don't want
  35         any buffer overflows, so we read only 255 bytes */
  36         if(count > 255)
  37                 count = 255;
  38         /* Here we read from buf to our_buf */
  39         copy_from_user(our_buf, buf, count);
  40         /* we write NULL to end the string */
  41         our_buf[count] = '\0';
  42         return count;
  43 }
  44
  45 int __init start_module(void)
  46 {
  47
  48         /* We create our entry */
  49         struct proc_dir_entry *de = create_proc_entry("test_proc", 0666, 0);
  50
  51         /* Set pointers to our functions reading and writing */
  52         de->read_proc = buf_read;
  53         de->write_proc = buf_write;
  54
  55         /* We initialize our_buf with some text. */
  56         sprintf(our_buf, "hello");
  57
  58         return 0 ;
  59 }
  60
  61 void __exit exit_module(void)
  62 {
  63         /* We delete our entry */
  64         remove_proc_entry("test_proc", NULL);
  65 }
  66
  67 module_init(start_module);
  68 module_exit(exit_module);