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.
62 */
63 static DEFINE_IDA(misc_minors_ida);
64
misc_minor_alloc(int minor)65 static int misc_minor_alloc(int minor)
66 {
67 int ret = 0;
68
69 if (minor == MISC_DYNAMIC_MINOR) {
70 /* allocate free id */
71 ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1,
72 MINORMASK, GFP_KERNEL);
73 } else {
74 ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL);
75 }
76 return ret;
77 }
78
misc_minor_free(int minor)79 static void misc_minor_free(int minor)
80 {
81 ida_free(&misc_minors_ida, minor);
82 }
83
84 #ifdef CONFIG_PROC_FS
misc_seq_start(struct seq_file * seq,loff_t * pos)85 static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
86 {
87 mutex_lock(&misc_mtx);
88 return seq_list_start(&misc_list, *pos);
89 }
90
misc_seq_next(struct seq_file * seq,void * v,loff_t * pos)91 static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
92 {
93 return seq_list_next(v, &misc_list, pos);
94 }
95
misc_seq_stop(struct seq_file * seq,void * v)96 static void misc_seq_stop(struct seq_file *seq, void *v)
97 {
98 mutex_unlock(&misc_mtx);
99 }
100
misc_seq_show(struct seq_file * seq,void * v)101 static int misc_seq_show(struct seq_file *seq, void *v)
102 {
103 const struct miscdevice *p = list_entry(v, struct miscdevice, list);
104
105 seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
106 return 0;
107 }
108
109
110 static const struct seq_operations misc_seq_ops = {
111 .start = misc_seq_start,
112 .next = misc_seq_next,
113 .stop = misc_seq_stop,
114 .show = misc_seq_show,
115 };
116 #endif
117
misc_open(struct inode * inode,struct file * file)118 static int misc_open(struct inode *inode, struct file *file)
119 {
120 int minor = iminor(inode);
121 struct miscdevice *c = NULL, *iter;
122 int err = -ENODEV;
123 const struct file_operations *new_fops = NULL;
124
125 mutex_lock(&misc_mtx);
126
127 list_for_each_entry(iter, &misc_list, list) {
128 if (iter->minor != minor)
129 continue;
130 c = iter;
131 new_fops = fops_get(iter->fops);
132 break;
133 }
134
135 if (!new_fops) {
136 mutex_unlock(&misc_mtx);
137 request_module("char-major-%d-%d", MISC_MAJOR, minor);
138 mutex_lock(&misc_mtx);
139
140 list_for_each_entry(iter, &misc_list, list) {
141 if (iter->minor != minor)
142 continue;
143 c = iter;
144 new_fops = fops_get(iter->fops);
145 break;
146 }
147 if (!new_fops)
148 goto fail;
149 }
150
151 /*
152 * Place the miscdevice in the file's
153 * private_data so it can be used by the
154 * file operations, including f_op->open below
155 */
156 file->private_data = c;
157
158 err = 0;
159 replace_fops(file, new_fops);
160 if (file->f_op->open)
161 err = file->f_op->open(inode, file);
162 fail:
163 mutex_unlock(&misc_mtx);
164 return err;
165 }
166
misc_devnode(const struct device * dev,umode_t * mode)167 static char *misc_devnode(const struct device *dev, umode_t *mode)
168 {
169 const struct miscdevice *c = dev_get_drvdata(dev);
170
171 if (mode && c->mode)
172 *mode = c->mode;
173 if (c->nodename)
174 return kstrdup(c->nodename, GFP_KERNEL);
175 return NULL;
176 }
177
178 static const struct class misc_class = {
179 .name = "misc",
180 .devnode = misc_devnode,
181 };
182
183 static const struct file_operations misc_fops = {
184 .owner = THIS_MODULE,
185 .open = misc_open,
186 .llseek = noop_llseek,
187 };
188
189 /**
190 * misc_register - register a miscellaneous device
191 * @misc: device structure
192 *
193 * Register a miscellaneous device with the kernel. If the minor
194 * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
195 * and placed in the minor field of the structure. For other cases
196 * the minor number requested is used.
197 *
198 * The structure passed is linked into the kernel and may not be
199 * destroyed until it has been unregistered. By default, an open()
200 * syscall to the device sets file->private_data to point to the
201 * structure. Drivers don't need open in fops for this.
202 *
203 * A zero is returned on success and a negative errno code for
204 * failure.
205 */
206
misc_register(struct miscdevice * misc)207 int misc_register(struct miscdevice *misc)
208 {
209 dev_t dev;
210 int err = 0;
211 bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
212
213 INIT_LIST_HEAD(&misc->list);
214
215 mutex_lock(&misc_mtx);
216
217 if (is_dynamic) {
218 int i = misc_minor_alloc(misc->minor);
219
220 if (i < 0) {
221 err = -EBUSY;
222 goto out;
223 }
224 misc->minor = i;
225 } else {
226 struct miscdevice *c;
227 int i;
228
229 list_for_each_entry(c, &misc_list, list) {
230 if (c->minor == misc->minor) {
231 err = -EBUSY;
232 goto out;
233 }
234 }
235
236 i = misc_minor_alloc(misc->minor);
237 if (i < 0) {
238 err = -EBUSY;
239 goto out;
240 }
241 }
242
243 dev = MKDEV(MISC_MAJOR, misc->minor);
244
245 misc->this_device =
246 device_create_with_groups(&misc_class, misc->parent, dev,
247 misc, misc->groups, "%s", misc->name);
248 if (IS_ERR(misc->this_device)) {
249 misc_minor_free(misc->minor);
250 if (is_dynamic) {
251 misc->minor = MISC_DYNAMIC_MINOR;
252 }
253 err = PTR_ERR(misc->this_device);
254 goto out;
255 }
256
257 /*
258 * Add it to the front, so that later devices can "override"
259 * earlier defaults
260 */
261 list_add(&misc->list, &misc_list);
262 out:
263 mutex_unlock(&misc_mtx);
264 return err;
265 }
266 EXPORT_SYMBOL(misc_register);
267
268 /**
269 * misc_deregister - unregister a miscellaneous device
270 * @misc: device to unregister
271 *
272 * Unregister a miscellaneous device that was previously
273 * successfully registered with misc_register().
274 */
275
misc_deregister(struct miscdevice * misc)276 void misc_deregister(struct miscdevice *misc)
277 {
278 if (WARN_ON(list_empty(&misc->list)))
279 return;
280
281 mutex_lock(&misc_mtx);
282 list_del(&misc->list);
283 device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
284 misc_minor_free(misc->minor);
285 mutex_unlock(&misc_mtx);
286 }
287 EXPORT_SYMBOL(misc_deregister);
288
misc_init(void)289 static int __init misc_init(void)
290 {
291 int err;
292 struct proc_dir_entry *ret;
293
294 ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
295 err = class_register(&misc_class);
296 if (err)
297 goto fail_remove;
298
299 err = -EIO;
300 if (__register_chrdev(MISC_MAJOR, 0, MINORMASK + 1, "misc", &misc_fops))
301 goto fail_printk;
302 return 0;
303
304 fail_printk:
305 pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
306 class_unregister(&misc_class);
307 fail_remove:
308 if (ret)
309 remove_proc_entry("misc", NULL);
310 return err;
311 }
312 subsys_initcall(misc_init);
313