Documentation/DocBook/procfs_example.c

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