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procfs_example.c

/*
 * procfs_example.c: an example proc interface
 *
 * Copyright (C) 2001, Erik Mouw (J.A.K.Mouw@its.tudelft.nl)
 *
 * This file accompanies the procfs-guide in the Linux kernel
 * source. Its main use is to demonstrate the concepts and
 * functions described in the guide.
 *
 * This software has been developed while working on the LART
 * computing board (http://www.lart.tudelft.nl/), which is
 * sponsored by the Mobile Multi-media Communications
 * (http://www.mmc.tudelft.nl/) and Ubiquitous Communications 
 * (http://www.ubicom.tudelft.nl/) projects.
 *
 * The author can be reached at:
 *
 *  Erik Mouw
 *  Information and Communication Theory Group
 *  Faculty of Information Technology and Systems
 *  Delft University of Technology
 *  P.O. Box 5031
 *  2600 GA Delft
 *  The Netherlands
 *
 *
 * This program is free software; you can redistribute
 * it and/or modify it under the terms of the GNU General
 * Public License as published by the Free Software
 * Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE.  See the GNU General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place,
 * Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <linux/jiffies.h>
#include <asm/uaccess.h>


#define MODULE_VERS "1.0"
#define MODULE_NAME "procfs_example"

#define FOOBAR_LEN 8

struct fb_data_t {
      char name[FOOBAR_LEN + 1];
      char value[FOOBAR_LEN + 1];
};


static struct proc_dir_entry *example_dir, *foo_file,
      *bar_file, *jiffies_file, *symlink;


struct fb_data_t foo_data, bar_data;


static int proc_read_jiffies(char *page, char **start,
                       off_t off, int count,
                       int *eof, void *data)
{
      int len;

      len = sprintf(page, "jiffies = %ld\n",
                      jiffies);

      return len;
}


static int proc_read_foobar(char *page, char **start,
                      off_t off, int count, 
                      int *eof, void *data)
{
      int len;
      struct fb_data_t *fb_data = (struct fb_data_t *)data;

      /* DON'T DO THAT - buffer overruns are bad */
      len = sprintf(page, "%s = '%s'\n", 
                  fb_data->name, fb_data->value);

      return len;
}


static int proc_write_foobar(struct file *file,
                       const char *buffer,
                       unsigned long count, 
                       void *data)
{
      int len;
      struct fb_data_t *fb_data = (struct fb_data_t *)data;

      if(count > FOOBAR_LEN)
            len = FOOBAR_LEN;
      else
            len = count;

      if(copy_from_user(fb_data->value, buffer, len))
            return -EFAULT;

      fb_data->value[len] = '\0';

      return len;
}


static int __init init_procfs_example(void)
{
      int rv = 0;

      /* create directory */
      example_dir = proc_mkdir(MODULE_NAME, NULL);
      if(example_dir == NULL) {
            rv = -ENOMEM;
            goto out;
      }
      
      example_dir->owner = THIS_MODULE;
      
      /* create jiffies using convenience function */
      jiffies_file = create_proc_read_entry("jiffies", 
                                    0444, example_dir, 
                                    proc_read_jiffies,
                                    NULL);
      if(jiffies_file == NULL) {
            rv  = -ENOMEM;
            goto no_jiffies;
      }

      jiffies_file->owner = THIS_MODULE;

      /* create foo and bar files using same callback
       * functions 
       */
      foo_file = create_proc_entry("foo", 0644, example_dir);
      if(foo_file == NULL) {
            rv = -ENOMEM;
            goto no_foo;
      }

      strcpy(foo_data.name, "foo");
      strcpy(foo_data.value, "foo");
      foo_file->data = &foo_data;
      foo_file->read_proc = proc_read_foobar;
      foo_file->write_proc = proc_write_foobar;
      foo_file->owner = THIS_MODULE;
            
      bar_file = create_proc_entry("bar", 0644, example_dir);
      if(bar_file == NULL) {
            rv = -ENOMEM;
            goto no_bar;
      }

      strcpy(bar_data.name, "bar");
      strcpy(bar_data.value, "bar");
      bar_file->data = &bar_data;
      bar_file->read_proc = proc_read_foobar;
      bar_file->write_proc = proc_write_foobar;
      bar_file->owner = THIS_MODULE;
            
      /* create symlink */
      symlink = proc_symlink("jiffies_too", example_dir, 
                         "jiffies");
      if(symlink == NULL) {
            rv = -ENOMEM;
            goto no_symlink;
      }

      symlink->owner = THIS_MODULE;

      /* everything OK */
      printk(KERN_INFO "%s %s initialised\n",
             MODULE_NAME, MODULE_VERS);
      return 0;

no_symlink:
      remove_proc_entry("tty", example_dir);
no_tty:
      remove_proc_entry("bar", example_dir);
no_bar:
      remove_proc_entry("foo", example_dir);
no_foo:
      remove_proc_entry("jiffies", example_dir);
no_jiffies:                   
      remove_proc_entry(MODULE_NAME, NULL);
out:
      return rv;
}


static void __exit cleanup_procfs_example(void)
{
      remove_proc_entry("jiffies_too", example_dir);
      remove_proc_entry("tty", example_dir);
      remove_proc_entry("bar", example_dir);
      remove_proc_entry("foo", example_dir);
      remove_proc_entry("jiffies", example_dir);
      remove_proc_entry(MODULE_NAME, NULL);

      printk(KERN_INFO "%s %s removed\n",
             MODULE_NAME, MODULE_VERS);
}


module_init(init_procfs_example);
module_exit(cleanup_procfs_example);

MODULE_AUTHOR("Erik Mouw");
MODULE_DESCRIPTION("procfs examples");

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