Documentation/DocBook/procfs_example.c

   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
  59 struct fb_data_t {
  60         char name[FOOBAR_LEN + 1];
  61         char value[FOOBAR_LEN + 1];
  62 };
  63
  64
  65 static struct proc_dir_entry *example_dir, *foo_file,
  66         *bar_file, *jiffies_file, *symlink;
  67
  68
  69 struct fb_data_t foo_data, bar_data;
  70
  71
  72 static 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
  85 static 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
 100 static 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
 122 static 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
 191 no_symlink:
 192         remove_proc_entry("bar", example_dir);
 193 no_bar:
 194         remove_proc_entry("foo", example_dir);
 195 no_foo:
 196         remove_proc_entry("jiffies", example_dir);
 197 no_jiffies:
 198         remove_proc_entry(MODULE_NAME, NULL);
 199 out:
 200         return rv;
 201 }
 202
 203
 204 static void __exit cleanup_procfs_example(void)
 205 {
 206         remove_proc_entry("jiffies_too", example_dir);
 207         remove_proc_entry("bar", example_dir);
 208         remove_proc_entry("foo", example_dir);
 209         remove_proc_entry("jiffies", example_dir);
 210         remove_proc_entry(MODULE_NAME, NULL);
 211
 212         printk(KERN_INFO "%s %s removed\n",
 213                MODULE_NAME, MODULE_VERS);
 214 }
 215
 216
 217 module_init(init_procfs_example);
 218 module_exit(cleanup_procfs_example);
 219
 220 MODULE_AUTHOR("Erik Mouw");
 221 MODULE_DESCRIPTION("procfs examples");
 222 MODULE_LICENSE("GPL");