drivers/char/misc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/drivers/char/misc.c
   4  *
   5  * Generic misc open routine by Johan Myreen
   6  *
   7  * Based on code from Linus
   8  *
   9  * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's
  10  *   changes incorporated into 0.97pl4
  11  *   by Peter Cervasio (pete%q106fm.uucp@wupost.wustl.edu) (08SEP92)
  12  *   See busmouse.c for particulars.
  13  *
  14  * Made things a lot mode modular - easy to compile in just one or two
  15  * of the misc drivers, as they are now completely independent. Linus.
  16  *
  17  * Support for loadable modules. 8-Sep-95 Philip Blundell <pjb27@cam.ac.uk>
  18  *
  19  * Fixed a failing symbol register to free the device registration
  20  *              Alan Cox <alan@lxorguk.ukuu.org.uk> 21-Jan-96
  21  *
  22  * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96
  23  *
  24  * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96
  25  *
  26  * Handling of mouse minor numbers for kerneld:
  27  *  Idea by Jacques Gelinas <jack@solucorp.qc.ca>,
  28  *  adapted by Bjorn Ekwall <bj0rn@blox.se>
  29  *  corrected by Alan Cox <alan@lxorguk.ukuu.org.uk>
  30  *
  31  * Changes for kmod (from kerneld):
  32  *      Cyrus Durgin <cider@speakeasy.org>
  33  *
  34  * Added devfs support. Richard Gooch <rgooch@atnf.csiro.au>  10-Jan-1998
  35  */
  36
  37 #include <linux/module.h>
  38
  39 #include <linux/fs.h>
  40 #include <linux/errno.h>
  41 #include <linux/miscdevice.h>
  42 #include <linux/kernel.h>
  43 #include <linux/major.h>
  44 #include <linux/mutex.h>
  45 #include <linux/proc_fs.h>
  46 #include <linux/seq_file.h>
  47 #include <linux/stat.h>
  48 #include <linux/init.h>
  49 #include <linux/device.h>
  50 #include <linux/tty.h>
  51 #include <linux/kmod.h>
  52 #include <linux/gfp.h>
  53
  54 /*
  55  * Head entry for the doubly linked miscdevice list
  56  */
  57 static LIST_HEAD(misc_list);
  58 static DEFINE_MUTEX(misc_mtx);
  59
  60 /*
  61  * Assigned numbers, used for dynamic minors
  62  */
  63 #define DYNAMIC_MINORS 128 /* like dynamic majors */
  64 static DEFINE_IDA(misc_minors_ida);
  65
  66 static int misc_minor_alloc(void)
  67 {
  68         int ret;
  69
  70         ret = ida_alloc_max(&misc_minors_ida, DYNAMIC_MINORS - 1, GFP_KERNEL);
  71         if (ret >= 0) {
  72                 ret = DYNAMIC_MINORS - ret - 1;
  73         } else {
  74                 ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1,
  75                                       MINORMASK, GFP_KERNEL);
  76         }
  77         return ret;
  78 }
  79
  80 static void misc_minor_free(int minor)
  81 {
  82         if (minor < DYNAMIC_MINORS)
  83                 ida_free(&misc_minors_ida, DYNAMIC_MINORS - minor - 1);
  84         else if (minor > MISC_DYNAMIC_MINOR)
  85                 ida_free(&misc_minors_ida, minor);
  86 }
  87
  88 #ifdef CONFIG_PROC_FS
  89 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
  90 {
  91         mutex_lock(&misc_mtx);
  92         return seq_list_start(&misc_list, *pos);
  93 }
  94
  95 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
  96 {
  97         return seq_list_next(v, &misc_list, pos);
  98 }
  99
 100 static void misc_seq_stop(struct seq_file *seq, void *v)
 101 {
 102         mutex_unlock(&misc_mtx);
 103 }
 104
 105 static int misc_seq_show(struct seq_file *seq, void *v)
 106 {
 107         const struct miscdevice *p = list_entry(v, struct miscdevice, list);
 108
 109         seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
 110         return 0;
 111 }
 112
 113
 114 static const struct seq_operations misc_seq_ops = {
 115         .start = misc_seq_start,
 116         .next  = misc_seq_next,
 117         .stop  = misc_seq_stop,
 118         .show  = misc_seq_show,
 119 };
 120 #endif
 121
 122 static int misc_open(struct inode *inode, struct file *file)
 123 {
 124         int minor = iminor(inode);
 125         struct miscdevice *c = NULL, *iter;
 126         int err = -ENODEV;
 127         const struct file_operations *new_fops = NULL;
 128
 129         mutex_lock(&misc_mtx);
 130
 131         list_for_each_entry(iter, &misc_list, list) {
 132                 if (iter->minor != minor)
 133                         continue;
 134                 c = iter;
 135                 new_fops = fops_get(iter->fops);
 136                 break;
 137         }
 138
 139         if (!new_fops) {
 140                 mutex_unlock(&misc_mtx);
 141                 request_module("char-major-%d-%d", MISC_MAJOR, minor);
 142                 mutex_lock(&misc_mtx);
 143
 144                 list_for_each_entry(iter, &misc_list, list) {
 145                         if (iter->minor != minor)
 146                                 continue;
 147                         c = iter;
 148                         new_fops = fops_get(iter->fops);
 149                         break;
 150                 }
 151                 if (!new_fops)
 152                         goto fail;
 153         }
 154
 155         /*
 156          * Place the miscdevice in the file's
 157          * private_data so it can be used by the
 158          * file operations, including f_op->open below
 159          */
 160         file->private_data = c;
 161
 162         err = 0;
 163         replace_fops(file, new_fops);
 164         if (file->f_op->open)
 165                 err = file->f_op->open(inode, file);
 166 fail:
 167         mutex_unlock(&misc_mtx);
 168         return err;
 169 }
 170
 171 static char *misc_devnode(const struct device *dev, umode_t *mode)
 172 {
 173         const struct miscdevice *c = dev_get_drvdata(dev);
 174
 175         if (mode && c->mode)
 176                 *mode = c->mode;
 177         if (c->nodename)
 178                 return kstrdup(c->nodename, GFP_KERNEL);
 179         return NULL;
 180 }
 181
 182 static const struct class misc_class = {
 183         .name           = "misc",
 184         .devnode        = misc_devnode,
 185 };
 186
 187 static const struct file_operations misc_fops = {
 188         .owner          = THIS_MODULE,
 189         .open           = misc_open,
 190         .llseek         = noop_llseek,
 191 };
 192
 193 /**
 194  *      misc_register   -       register a miscellaneous device
 195  *      @misc: device structure
 196  *
 197  *      Register a miscellaneous device with the kernel. If the minor
 198  *      number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
 199  *      and placed in the minor field of the structure. For other cases
 200  *      the minor number requested is used.
 201  *
 202  *      The structure passed is linked into the kernel and may not be
 203  *      destroyed until it has been unregistered. By default, an open()
 204  *      syscall to the device sets file->private_data to point to the
 205  *      structure. Drivers don't need open in fops for this.
 206  *
 207  *      A zero is returned on success and a negative errno code for
 208  *      failure.
 209  */
 210
 211 int misc_register(struct miscdevice *misc)
 212 {
 213         dev_t dev;
 214         int err = 0;
 215         bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
 216
 217         INIT_LIST_HEAD(&misc->list);
 218
 219         mutex_lock(&misc_mtx);
 220
 221         if (is_dynamic) {
 222                 int i = misc_minor_alloc();
 223
 224                 if (i < 0) {
 225                         err = -EBUSY;
 226                         goto out;
 227                 }
 228                 misc->minor = i;
 229         } else {
 230                 struct miscdevice *c;
 231
 232                 list_for_each_entry(c, &misc_list, list) {
 233                         if (c->minor == misc->minor) {
 234                                 err = -EBUSY;
 235                                 goto out;
 236                         }
 237                 }
 238         }
 239
 240         dev = MKDEV(MISC_MAJOR, misc->minor);
 241
 242         misc->this_device =
 243                 device_create_with_groups(&misc_class, misc->parent, dev,
 244                                           misc, misc->groups, "%s", misc->name);
 245         if (IS_ERR(misc->this_device)) {
 246                 if (is_dynamic) {
 247                         misc_minor_free(misc->minor);
 248                         misc->minor = MISC_DYNAMIC_MINOR;
 249                 }
 250                 err = PTR_ERR(misc->this_device);
 251                 goto out;
 252         }
 253
 254         /*
 255          * Add it to the front, so that later devices can "override"
 256          * earlier defaults
 257          */
 258         list_add(&misc->list, &misc_list);
 259  out:
 260         mutex_unlock(&misc_mtx);
 261         return err;
 262 }
 263 EXPORT_SYMBOL(misc_register);
 264
 265 /**
 266  *      misc_deregister - unregister a miscellaneous device
 267  *      @misc: device to unregister
 268  *
 269  *      Unregister a miscellaneous device that was previously
 270  *      successfully registered with misc_register().
 271  */
 272
 273 void misc_deregister(struct miscdevice *misc)
 274 {
 275         if (WARN_ON(list_empty(&misc->list)))
 276                 return;
 277
 278         mutex_lock(&misc_mtx);
 279         list_del(&misc->list);
 280         device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
 281         misc_minor_free(misc->minor);
 282         mutex_unlock(&misc_mtx);
 283 }
 284 EXPORT_SYMBOL(misc_deregister);
 285
 286 static int __init misc_init(void)
 287 {
 288         int err;
 289         struct proc_dir_entry *ret;
 290
 291         ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
 292         err = class_register(&misc_class);
 293         if (err)
 294                 goto fail_remove;
 295
 296         err = -EIO;
 297         if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
 298                 goto fail_printk;
 299         return 0;
 300
 301 fail_printk:
 302         pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
 303         class_unregister(&misc_class);
 304 fail_remove:
 305         if (ret)
 306                 remove_proc_entry("misc", NULL);
 307         return err;
 308 }
 309 subsys_initcall(misc_init);