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(void)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
misc_minor_free(int minor)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
misc_seq_start(struct seq_file * seq,loff_t * pos)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
misc_seq_next(struct seq_file * seq,void * v,loff_t * pos)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
misc_seq_stop(struct seq_file * seq,void * v)100 static void misc_seq_stop(struct seq_file *seq, void *v)
101 {
102 mutex_unlock(&misc_mtx);
103 }
104
misc_seq_show(struct seq_file * seq,void * v)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
misc_open(struct inode * inode,struct file * file)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
misc_devnode(const struct device * dev,umode_t * mode)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
misc_register(struct miscdevice * misc)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
misc_deregister(struct miscdevice * misc)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
misc_init(void)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);
310
