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