drivers/char/misc.c

   1 /*
   2  * linux/drivers/char/misc.c
   3  *
   4  * Generic misc open routine by Johan Myreen
   5  *
   6  * Based on code from Linus
   7  *
   8  * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's
   9  *   changes incorporated into 0.97pl4
  10  *   by Peter Cervasio (pete%q106fm.uucp@wupost.wustl.edu) (08SEP92)
  11  *   See busmouse.c for particulars.
  12  *
  13  * Made things a lot mode modular - easy to compile in just one or two
  14  * of the misc drivers, as they are now completely independent. Linus.
  15  *
  16  * Support for loadable modules. 8-Sep-95 Philip Blundell <pjb27@cam.ac.uk>
  17  *
  18  * Fixed a failing symbol register to free the device registration
  19  *              Alan Cox <alan@lxorguk.ukuu.org.uk> 21-Jan-96
  20  *
  21  * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96
  22  *
  23  * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96
  24  *
  25  * Handling of mouse minor numbers for kerneld:
  26  *  Idea by Jacques Gelinas <jack@solucorp.qc.ca>,
  27  *  adapted by Bjorn Ekwall <bj0rn@blox.se>
  28  *  corrected by Alan Cox <alan@lxorguk.ukuu.org.uk>
  29  *
  30  * Changes for kmod (from kerneld):
  31  *      Cyrus Durgin <cider@speakeasy.org>
  32  *
  33  * Added devfs support. Richard Gooch <rgooch@atnf.csiro.au>  10-Jan-1998
  34  */
  35
  36 #include <linux/module.h>
  37
  38 #include <linux/fs.h>
  39 #include <linux/errno.h>
  40 #include <linux/miscdevice.h>
  41 #include <linux/kernel.h>
  42 #include <linux/major.h>
  43 #include <linux/mutex.h>
  44 #include <linux/proc_fs.h>
  45 #include <linux/seq_file.h>
  46 #include <linux/stat.h>
  47 #include <linux/init.h>
  48 #include <linux/device.h>
  49 #include <linux/tty.h>
  50 #include <linux/kmod.h>
  51 #include <linux/gfp.h>
  52
  53 /*
  54  * Head entry for the doubly linked miscdevice list
  55  */
  56 static LIST_HEAD(misc_list);
  57 static DEFINE_MUTEX(misc_mtx);
  58
  59 /*
  60  * Assigned numbers, used for dynamic minors
  61  */
  62 #define DYNAMIC_MINORS 64 /* like dynamic majors */
  63 static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);
  64
  65 #ifdef CONFIG_PROC_FS
  66 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
  67 {
  68         mutex_lock(&misc_mtx);
  69         return seq_list_start(&misc_list, *pos);
  70 }
  71
  72 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
  73 {
  74         return seq_list_next(v, &misc_list, pos);
  75 }
  76
  77 static void misc_seq_stop(struct seq_file *seq, void *v)
  78 {
  79         mutex_unlock(&misc_mtx);
  80 }
  81
  82 static int misc_seq_show(struct seq_file *seq, void *v)
  83 {
  84         const struct miscdevice *p = list_entry(v, struct miscdevice, list);
  85
  86         seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
  87         return 0;
  88 }
  89
  90
  91 static const struct seq_operations misc_seq_ops = {
  92         .start = misc_seq_start,
  93         .next  = misc_seq_next,
  94         .stop  = misc_seq_stop,
  95         .show  = misc_seq_show,
  96 };
  97
  98 static int misc_seq_open(struct inode *inode, struct file *file)
  99 {
 100         return seq_open(file, &misc_seq_ops);
 101 }
 102
 103 static const struct file_operations misc_proc_fops = {
 104         .owner   = THIS_MODULE,
 105         .open    = misc_seq_open,
 106         .read    = seq_read,
 107         .llseek  = seq_lseek,
 108         .release = seq_release,
 109 };
 110 #endif
 111
 112 static int misc_open(struct inode *inode, struct file *file)
 113 {
 114         int minor = iminor(inode);
 115         struct miscdevice *c;
 116         int err = -ENODEV;
 117         const struct file_operations *new_fops = NULL;
 118
 119         mutex_lock(&misc_mtx);
 120
 121         list_for_each_entry(c, &misc_list, list) {
 122                 if (c->minor == minor) {
 123                         new_fops = fops_get(c->fops);
 124                         break;
 125                 }
 126         }
 127
 128         if (!new_fops) {
 129                 mutex_unlock(&misc_mtx);
 130                 request_module("char-major-%d-%d", MISC_MAJOR, minor);
 131                 mutex_lock(&misc_mtx);
 132
 133                 list_for_each_entry(c, &misc_list, list) {
 134                         if (c->minor == minor) {
 135                                 new_fops = fops_get(c->fops);
 136                                 break;
 137                         }
 138                 }
 139                 if (!new_fops)
 140                         goto fail;
 141         }
 142
 143         /*
 144          * Place the miscdevice in the file's
 145          * private_data so it can be used by the
 146          * file operations, including f_op->open below
 147          */
 148         file->private_data = c;
 149
 150         err = 0;
 151         replace_fops(file, new_fops);
 152         if (file->f_op->open)
 153                 err = file->f_op->open(inode, file);
 154 fail:
 155         mutex_unlock(&misc_mtx);
 156         return err;
 157 }
 158
 159 static struct class *misc_class;
 160
 161 static const struct file_operations misc_fops = {
 162         .owner          = THIS_MODULE,
 163         .open           = misc_open,
 164         .llseek         = noop_llseek,
 165 };
 166
 167 /**
 168  *      misc_register   -       register a miscellaneous device
 169  *      @misc: device structure
 170  *
 171  *      Register a miscellaneous device with the kernel. If the minor
 172  *      number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
 173  *      and placed in the minor field of the structure. For other cases
 174  *      the minor number requested is used.
 175  *
 176  *      The structure passed is linked into the kernel and may not be
 177  *      destroyed until it has been unregistered. By default, an open()
 178  *      syscall to the device sets file->private_data to point to the
 179  *      structure. Drivers don't need open in fops for this.
 180  *
 181  *      A zero is returned on success and a negative errno code for
 182  *      failure.
 183  */
 184
 185 int misc_register(struct miscdevice *misc)
 186 {
 187         dev_t dev;
 188         int err = 0;
 189         bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
 190
 191         INIT_LIST_HEAD(&misc->list);
 192
 193         mutex_lock(&misc_mtx);
 194
 195         if (is_dynamic) {
 196                 int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
 197
 198                 if (i >= DYNAMIC_MINORS) {
 199                         err = -EBUSY;
 200                         goto out;
 201                 }
 202                 misc->minor = DYNAMIC_MINORS - i - 1;
 203                 set_bit(i, misc_minors);
 204         } else {
 205                 struct miscdevice *c;
 206
 207                 list_for_each_entry(c, &misc_list, list) {
 208                         if (c->minor == misc->minor) {
 209                                 err = -EBUSY;
 210                                 goto out;
 211                         }
 212                 }
 213         }
 214
 215         dev = MKDEV(MISC_MAJOR, misc->minor);
 216
 217         misc->this_device =
 218                 device_create_with_groups(misc_class, misc->parent, dev,
 219                                           misc, misc->groups, "%s", misc->name);
 220         if (IS_ERR(misc->this_device)) {
 221                 if (is_dynamic) {
 222                         int i = DYNAMIC_MINORS - misc->minor - 1;
 223
 224                         if (i < DYNAMIC_MINORS && i >= 0)
 225                                 clear_bit(i, misc_minors);
 226                         misc->minor = MISC_DYNAMIC_MINOR;
 227                 }
 228                 err = PTR_ERR(misc->this_device);
 229                 goto out;
 230         }
 231
 232         /*
 233          * Add it to the front, so that later devices can "override"
 234          * earlier defaults
 235          */
 236         list_add(&misc->list, &misc_list);
 237  out:
 238         mutex_unlock(&misc_mtx);
 239         return err;
 240 }
 241
 242 /**
 243  *      misc_deregister - unregister a miscellaneous device
 244  *      @misc: device to unregister
 245  *
 246  *      Unregister a miscellaneous device that was previously
 247  *      successfully registered with misc_register().
 248  */
 249
 250 void misc_deregister(struct miscdevice *misc)
 251 {
 252         int i = DYNAMIC_MINORS - misc->minor - 1;
 253
 254         if (WARN_ON(list_empty(&misc->list)))
 255                 return;
 256
 257         mutex_lock(&misc_mtx);
 258         list_del(&misc->list);
 259         device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
 260         if (i < DYNAMIC_MINORS && i >= 0)
 261                 clear_bit(i, misc_minors);
 262         mutex_unlock(&misc_mtx);
 263 }
 264
 265 EXPORT_SYMBOL(misc_register);
 266 EXPORT_SYMBOL(misc_deregister);
 267
 268 static char *misc_devnode(struct device *dev, umode_t *mode)
 269 {
 270         struct miscdevice *c = dev_get_drvdata(dev);
 271
 272         if (mode && c->mode)
 273                 *mode = c->mode;
 274         if (c->nodename)
 275                 return kstrdup(c->nodename, GFP_KERNEL);
 276         return NULL;
 277 }
 278
 279 static int __init misc_init(void)
 280 {
 281         int err;
 282         struct proc_dir_entry *ret;
 283
 284         ret = proc_create("misc", 0, NULL, &misc_proc_fops);
 285         misc_class = class_create(THIS_MODULE, "misc");
 286         err = PTR_ERR(misc_class);
 287         if (IS_ERR(misc_class))
 288                 goto fail_remove;
 289
 290         err = -EIO;
 291         if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
 292                 goto fail_printk;
 293         misc_class->devnode = misc_devnode;
 294         return 0;
 295
 296 fail_printk:
 297         pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
 298         class_destroy(misc_class);
 299 fail_remove:
 300         if (ret)
 301                 remove_proc_entry("misc", NULL);
 302         return err;
 303 }
 304 subsys_initcall(misc_init);