LXR linux/Documentation/DocBook/procfs

   1/*
   2 * procfs_example.c: an example proc interface
   3 *
   4 * Copyright (C) 2001, Erik Mouw (J.A.K.Mouw@its.tudelft.nl)
   5 *
   6 * This file accompanies the procfs-guide in the Linux kernel
   7 * source. Its main use is to demonstrate the concepts and
   8 * functions described in the guide.
   9 *
  10 * This software has been developed while working on the LART
  11 * computing board (http://www.lart.tudelft.nl/), which is
  12 * sponsored by the Mobile Multi-media Communications
  13 * (http://www.mmc.tudelft.nl/) and Ubiquitous Communications 
  14 * (http://www.ubicom.tudelft.nl/) projects.
  15 *
  16 * The author can be reached at:
  17 *
  18 *  Erik Mouw
  19 *  Information and Communication Theory Group
  20 *  Faculty of Information Technology and Systems
  21 *  Delft University of Technology
  22 *  P.O. Box 5031
  23 *  2600 GA Delft
  24 *  The Netherlands
  25 *
  26 *
  27 * This program is free software; you can redistribute
  28 * it and/or modify it under the terms of the GNU General
  29 * Public License as published by the Free Software
  30 * Foundation; either version 2 of the License, or (at your
  31 * option) any later version.
  32 *
  33 * This program is distributed in the hope that it will be
  34 * useful, but WITHOUT ANY WARRANTY; without even the implied
  35 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  36 * PURPOSE.  See the GNU General Public License for more
  37 * details.
  38 * 
  39 * You should have received a copy of the GNU General Public
  40 * License along with this program; if not, write to the
  41 * Free Software Foundation, Inc., 59 Temple Place,
  42 * Suite 330, Boston, MA  02111-1307  USA
  43 *
  44 */
  45
  46#include <linux/module.h>
  47#include <linux/kernel.h>
  48#include <linux/init.h>
  49#include <linux/proc_fs.h>
  50#include <linux/jiffies.h>
  51#include <asm/uaccess.h>
  52
  53
  54#define MODULE_VERS "1.0"
  55#define MODULE_NAME "procfs_example"
  56
  57#define FOOBAR_LEN 8
  58
  59struct fb_data_t {
  60        char name[FOOBAR_LEN + 1];
  61        char value[FOOBAR_LEN + 1];
  62};
  63
  64
  65static struct proc_dir_entry *example_dir, *foo_file,
  66        *bar_file, *jiffies_file, *symlink;
  67
  68
  69struct fb_data_t foo_data, bar_data;
  70
  71
  72static int proc_read_jiffies(char *page, char **start,
  73                             off_t off, int count,
  74                             int *eof, void *data)
  75{
  76        int len;
  77
  78        len = sprintf(page, "jiffies = %ld\n",
  79                      jiffies);
  80
  81        return len;
  82}
  83
  84
  85static int proc_read_foobar(char *page, char **start,
  86                            off_t off, int count, 
  87                            int *eof, void *data)
  88{
  89        int len;
  90        struct fb_data_t *fb_data = (struct fb_data_t *)data;
  91
  92        /* DON'T DO THAT - buffer overruns are bad */
  93        len = sprintf(page, "%s = '%s'\n", 
  94                      fb_data->name, fb_data->value);
  95
  96        return len;
  97}
  98
  99
 100static int proc_write_foobar(struct file *file,
 101                             const char *buffer,
 102                             unsigned long count, 
 103                             void *data)
 104{
 105        int len;
 106        struct fb_data_t *fb_data = (struct fb_data_t *)data;
 107
 108        if(count > FOOBAR_LEN)
 109                len = FOOBAR_LEN;
 110        else
 111                len = count;
 112
 113        if(copy_from_user(fb_data->value, buffer, len))
 114                return -EFAULT;
 115
 116        fb_data->value[len] = '\0';
 117
 118        return len;
 119}
 120
 121
 122static int __init init_procfs_example(void)
 123{
 124        int rv = 0;
 125
 126        /* create directory */
 127        example_dir = proc_mkdir(MODULE_NAME, NULL);
 128        if(example_dir == NULL) {
 129                rv = -ENOMEM;
 130                goto out;
 131        }
 132        
 133        example_dir->owner = THIS_MODULE;
 134        
 135        /* create jiffies using convenience function */
 136        jiffies_file = create_proc_read_entry("jiffies", 
 137                                              0444, example_dir, 
 138                                              proc_read_jiffies,
 139                                              NULL);
 140        if(jiffies_file == NULL) {
 141                rv  = -ENOMEM;
 142                goto no_jiffies;
 143        }
 144
 145        jiffies_file->owner = THIS_MODULE;
 146
 147        /* create foo and bar files using same callback
 148         * functions 
 149         */
 150        foo_file = create_proc_entry("foo", 0644, example_dir);
 151        if(foo_file == NULL) {
 152                rv = -ENOMEM;
 153                goto no_foo;
 154        }
 155
 156        strcpy(foo_data.name, "foo");
 157        strcpy(foo_data.value, "foo");
 158        foo_file->data = &foo_data;
 159        foo_file->read_proc = proc_read_foobar;
 160        foo_file->write_proc = proc_write_foobar;
 161        foo_file->owner = THIS_MODULE;
 162                
 163        bar_file = create_proc_entry("bar", 0644, example_dir);
 164        if(bar_file == NULL) {
 165                rv = -ENOMEM;
 166                goto no_bar;
 167        }
 168
 169        strcpy(bar_data.name, "bar");
 170        strcpy(bar_data.value, "bar");
 171        bar_file->data = &bar_data;
 172        bar_file->read_proc = proc_read_foobar;
 173        bar_file->write_proc = proc_write_foobar;
 174        bar_file->owner = THIS_MODULE;
 175                
 176        /* create symlink */
 177        symlink = proc_symlink("jiffies_too", example_dir, 
 178                               "jiffies");
 179        if(symlink == NULL) {
 180                rv = -ENOMEM;
 181                goto no_symlink;
 182        }
 183
 184        symlink->owner = THIS_MODULE;
 185
 186        /* everything OK */
 187        printk(KERN_INFO "%s %s initialised\n",
 188               MODULE_NAME, MODULE_VERS);
 189        return 0;
 190
 191no_symlink:
 192        remove_proc_entry("tty", example_dir);
 193no_tty:
 194        remove_proc_entry("bar", example_dir);
 195no_bar:
 196        remove_proc_entry("foo", example_dir);
 197no_foo:
 198        remove_proc_entry("jiffies", example_dir);
 199no_jiffies:                           
 200        remove_proc_entry(MODULE_NAME, NULL);
 201out:
 202        return rv;
 203}
 204
 205
 206static void __exit cleanup_procfs_example(void)
 207{
 208        remove_proc_entry("jiffies_too", example_dir);
 209        remove_proc_entry("tty", example_dir);
 210        remove_proc_entry("bar", example_dir);
 211        remove_proc_entry("foo", example_dir);
 212        remove_proc_entry("jiffies", example_dir);
 213        remove_proc_entry(MODULE_NAME, NULL);
 214
 215        printk(KERN_INFO "%s %s removed\n",
 216               MODULE_NAME, MODULE_VERS);
 217}
 218
 219
 220module_init(init_procfs_example);
 221module_exit(cleanup_procfs_example);
 222
 223MODULE_AUTHOR("Erik Mouw");
 224MODULE_DESCRIPTION("procfs examples");
 225