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
misc_minor_alloc(int minor)66 static int misc_minor_alloc(int minor)
67 {
68 int ret = 0;
69
70 if (minor == MISC_DYNAMIC_MINOR) {
71 /* allocate free id */
72 ret = ida_alloc_max(&misc_minors_ida, DYNAMIC_MINORS - 1, GFP_KERNEL);
73 if (ret >= 0) {
74 ret = DYNAMIC_MINORS - ret - 1;
75 } else {
76 ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1,
77 MINORMASK, GFP_KERNEL);
78 }
79 } else {
80 /* specific minor, check if it is in dynamic or misc dynamic range */
81 if (minor < DYNAMIC_MINORS) {
82 minor = DYNAMIC_MINORS - minor - 1;
83 ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL);
84 } else if (minor > MISC_DYNAMIC_MINOR) {
85 ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL);
86 } else {
87 /* case of non-dynamic minors, no need to allocate id */
88 ret = 0;
89 }
90 }
91 return ret;
92 }
93
misc_minor_free(int minor)94 static void misc_minor_free(int minor)
95 {
96 if (minor < DYNAMIC_MINORS)
97 ida_free(&misc_minors_ida, DYNAMIC_MINORS - minor - 1);
98 else if (minor > MISC_DYNAMIC_MINOR)
99 ida_free(&misc_minors_ida, minor);
100 }
101
102 #ifdef CONFIG_PROC_FS
misc_seq_start(struct seq_file * seq,loff_t * pos)103 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
104 {
105 mutex_lock(&misc_mtx);
106 return seq_list_start(&misc_list, *pos);
107 }
108
misc_seq_next(struct seq_file * seq,void * v,loff_t * pos)109 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
110 {
111 return seq_list_next(v, &misc_list, pos);
112 }
113
misc_seq_stop(struct seq_file * seq,void * v)114 static void misc_seq_stop(struct seq_file *seq, void *v)
115 {
116 mutex_unlock(&misc_mtx);
117 }
118
misc_seq_show(struct seq_file * seq,void * v)119 static int misc_seq_show(struct seq_file *seq, void *v)
120 {
121 const struct miscdevice *p = list_entry(v, struct miscdevice, list);
122
123 seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
124 return 0;
125 }
126
127
128 static const struct seq_operations misc_seq_ops = {
129 .start = misc_seq_start,
130 .next = misc_seq_next,
131 .stop = misc_seq_stop,
132 .show = misc_seq_show,
133 };
134 #endif
135
misc_open(struct inode * inode,struct file * file)136 static int misc_open(struct inode *inode, struct file *file)
137 {
138 int minor = iminor(inode);
139 struct miscdevice *c = NULL, *iter;
140 int err = -ENODEV;
141 const struct file_operations *new_fops = NULL;
142
143 mutex_lock(&misc_mtx);
144
145 list_for_each_entry(iter, &misc_list, list) {
146 if (iter->minor != minor)
147 continue;
148 c = iter;
149 new_fops = fops_get(iter->fops);
150 break;
151 }
152
153 if (!new_fops) {
154 mutex_unlock(&misc_mtx);
155 request_module("char-major-%d-%d", MISC_MAJOR, minor);
156 mutex_lock(&misc_mtx);
157
158 list_for_each_entry(iter, &misc_list, list) {
159 if (iter->minor != minor)
160 continue;
161 c = iter;
162 new_fops = fops_get(iter->fops);
163 break;
164 }
165 if (!new_fops)
166 goto fail;
167 }
168
169 /*
170 * Place the miscdevice in the file's
171 * private_data so it can be used by the
172 * file operations, including f_op->open below
173 */
174 file->private_data = c;
175
176 err = 0;
177 replace_fops(file, new_fops);
178 if (file->f_op->open)
179 err = file->f_op->open(inode, file);
180 fail:
181 mutex_unlock(&misc_mtx);
182 return err;
183 }
184
misc_devnode(const struct device * dev,umode_t * mode)185 static char *misc_devnode(const struct device *dev, umode_t *mode)
186 {
187 const struct miscdevice *c = dev_get_drvdata(dev);
188
189 if (mode && c->mode)
190 *mode = c->mode;
191 if (c->nodename)
192 return kstrdup(c->nodename, GFP_KERNEL);
193 return NULL;
194 }
195
196 static const struct class misc_class = {
197 .name = "misc",
198 .devnode = misc_devnode,
199 };
200
201 static const struct file_operations misc_fops = {
202 .owner = THIS_MODULE,
203 .open = misc_open,
204 .llseek = noop_llseek,
205 };
206
207 /**
208 * misc_register - register a miscellaneous device
209 * @misc: device structure
210 *
211 * Register a miscellaneous device with the kernel. If the minor
212 * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
213 * and placed in the minor field of the structure. For other cases
214 * the minor number requested is used.
215 *
216 * The structure passed is linked into the kernel and may not be
217 * destroyed until it has been unregistered. By default, an open()
218 * syscall to the device sets file->private_data to point to the
219 * structure. Drivers don't need open in fops for this.
220 *
221 * A zero is returned on success and a negative errno code for
222 * failure.
223 */
224
misc_register(struct miscdevice * misc)225 int misc_register(struct miscdevice *misc)
226 {
227 dev_t dev;
228 int err = 0;
229 bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
230
231 INIT_LIST_HEAD(&misc->list);
232
233 mutex_lock(&misc_mtx);
234
235 if (is_dynamic) {
236 int i = misc_minor_alloc(misc->minor);
237
238 if (i < 0) {
239 err = -EBUSY;
240 goto out;
241 }
242 misc->minor = i;
243 } else {
244 struct miscdevice *c;
245 int i;
246
247 list_for_each_entry(c, &misc_list, list) {
248 if (c->minor == misc->minor) {
249 err = -EBUSY;
250 goto out;
251 }
252 }
253
254 i = misc_minor_alloc(misc->minor);
255 if (i < 0) {
256 err = -EBUSY;
257 goto out;
258 }
259 }
260
261 dev = MKDEV(MISC_MAJOR, misc->minor);
262
263 misc->this_device =
264 device_create_with_groups(&misc_class, misc->parent, dev,
265 misc, misc->groups, "%s", misc->name);
266 if (IS_ERR(misc->this_device)) {
267 if (is_dynamic) {
268 misc_minor_free(misc->minor);
269 misc->minor = MISC_DYNAMIC_MINOR;
270 }
271 err = PTR_ERR(misc->this_device);
272 goto out;
273 }
274
275 /*
276 * Add it to the front, so that later devices can "override"
277 * earlier defaults
278 */
279 list_add(&misc->list, &misc_list);
280 out:
281 mutex_unlock(&misc_mtx);
282 return err;
283 }
284 EXPORT_SYMBOL(misc_register);
285
286 /**
287 * misc_deregister - unregister a miscellaneous device
288 * @misc: device to unregister
289 *
290 * Unregister a miscellaneous device that was previously
291 * successfully registered with misc_register().
292 */
293
misc_deregister(struct miscdevice * misc)294 void misc_deregister(struct miscdevice *misc)
295 {
296 if (WARN_ON(list_empty(&misc->list)))
297 return;
298
299 mutex_lock(&misc_mtx);
300 list_del(&misc->list);
301 device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
302 misc_minor_free(misc->minor);
303 mutex_unlock(&misc_mtx);
304 }
305 EXPORT_SYMBOL(misc_deregister);
306
misc_init(void)307 static int __init misc_init(void)
308 {
309 int err;
310 struct proc_dir_entry *ret;
311
312 ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
313 err = class_register(&misc_class);
314 if (err)
315 goto fail_remove;
316
317 err = -EIO;
318 if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
319 goto fail_printk;
320 return 0;
321
322 fail_printk:
323 pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
324 class_unregister(&misc_class);
325 fail_remove:
326 if (ret)
327 remove_proc_entry("misc", NULL);
328 return err;
329 }
330 subsys_initcall(misc_init);
331