Line data Source code
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
67 0 : static void *misc_seq_start(struct seq_file *seq, loff_t *pos)
68 : {
69 0 : mutex_lock(&misc_mtx);
70 0 : return seq_list_start(&misc_list, *pos);
71 : }
72 :
73 0 : static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos)
74 : {
75 0 : return seq_list_next(v, &misc_list, pos);
76 : }
77 :
78 0 : static void misc_seq_stop(struct seq_file *seq, void *v)
79 : {
80 0 : mutex_unlock(&misc_mtx);
81 0 : }
82 :
83 0 : static int misc_seq_show(struct seq_file *seq, void *v)
84 : {
85 0 : const struct miscdevice *p = list_entry(v, struct miscdevice, list);
86 :
87 0 : seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : "");
88 0 : 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 :
100 0 : static int misc_open(struct inode *inode, struct file *file)
101 : {
102 0 : int minor = iminor(inode);
103 0 : struct miscdevice *c;
104 0 : int err = -ENODEV;
105 0 : const struct file_operations *new_fops = NULL;
106 :
107 0 : mutex_lock(&misc_mtx);
108 :
109 0 : list_for_each_entry(c, &misc_list, list) {
110 0 : if (c->minor == minor) {
111 0 : new_fops = fops_get(c->fops);
112 : break;
113 : }
114 : }
115 :
116 0 : if (!new_fops) {
117 0 : mutex_unlock(&misc_mtx);
118 0 : request_module("char-major-%d-%d", MISC_MAJOR, minor);
119 0 : mutex_lock(&misc_mtx);
120 :
121 0 : list_for_each_entry(c, &misc_list, list) {
122 0 : if (c->minor == minor) {
123 0 : new_fops = fops_get(c->fops);
124 : break;
125 : }
126 : }
127 0 : if (!new_fops)
128 0 : 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 0 : file->private_data = c;
137 :
138 0 : err = 0;
139 0 : replace_fops(file, new_fops);
140 0 : if (file->f_op->open)
141 0 : err = file->f_op->open(inode, file);
142 0 : fail:
143 0 : mutex_unlock(&misc_mtx);
144 0 : 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 :
173 3 : int misc_register(struct miscdevice *misc)
174 : {
175 3 : dev_t dev;
176 3 : int err = 0;
177 3 : bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
178 :
179 3 : INIT_LIST_HEAD(&misc->list);
180 :
181 3 : mutex_lock(&misc_mtx);
182 :
183 3 : if (is_dynamic) {
184 0 : int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
185 :
186 0 : if (i >= DYNAMIC_MINORS) {
187 0 : err = -EBUSY;
188 0 : goto out;
189 : }
190 0 : misc->minor = DYNAMIC_MINORS - i - 1;
191 0 : set_bit(i, misc_minors);
192 : } else {
193 3 : struct miscdevice *c;
194 :
195 6 : list_for_each_entry(c, &misc_list, list) {
196 3 : if (c->minor == misc->minor) {
197 0 : err = -EBUSY;
198 0 : goto out;
199 : }
200 : }
201 : }
202 :
203 3 : dev = MKDEV(MISC_MAJOR, misc->minor);
204 :
205 6 : misc->this_device =
206 3 : device_create_with_groups(misc_class, misc->parent, dev,
207 : misc, misc->groups, "%s", misc->name);
208 3 : if (IS_ERR(misc->this_device)) {
209 0 : if (is_dynamic) {
210 0 : int i = DYNAMIC_MINORS - misc->minor - 1;
211 :
212 0 : if (i < DYNAMIC_MINORS && i >= 0)
213 0 : clear_bit(i, misc_minors);
214 0 : misc->minor = MISC_DYNAMIC_MINOR;
215 : }
216 0 : err = PTR_ERR(misc->this_device);
217 0 : goto out;
218 : }
219 :
220 : /*
221 : * Add it to the front, so that later devices can "override"
222 : * earlier defaults
223 : */
224 3 : list_add(&misc->list, &misc_list);
225 3 : out:
226 3 : mutex_unlock(&misc_mtx);
227 3 : 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 :
239 0 : void misc_deregister(struct miscdevice *misc)
240 : {
241 0 : int i = DYNAMIC_MINORS - misc->minor - 1;
242 :
243 0 : if (WARN_ON(list_empty(&misc->list)))
244 : return;
245 :
246 0 : mutex_lock(&misc_mtx);
247 0 : list_del(&misc->list);
248 0 : device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
249 0 : if (i < DYNAMIC_MINORS && i >= 0)
250 0 : clear_bit(i, misc_minors);
251 0 : mutex_unlock(&misc_mtx);
252 : }
253 : EXPORT_SYMBOL(misc_deregister);
254 :
255 15 : static char *misc_devnode(struct device *dev, umode_t *mode)
256 : {
257 15 : struct miscdevice *c = dev_get_drvdata(dev);
258 :
259 15 : if (mode && c->mode)
260 0 : *mode = c->mode;
261 15 : if (c->nodename)
262 10 : return kstrdup(c->nodename, GFP_KERNEL);
263 : return NULL;
264 : }
265 :
266 1 : static int __init misc_init(void)
267 : {
268 1 : int err;
269 1 : struct proc_dir_entry *ret;
270 :
271 1 : ret = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
272 1 : misc_class = class_create(THIS_MODULE, "misc");
273 1 : err = PTR_ERR(misc_class);
274 1 : if (IS_ERR(misc_class))
275 0 : goto fail_remove;
276 :
277 1 : err = -EIO;
278 1 : if (register_chrdev(MISC_MAJOR, "misc", &misc_fops))
279 0 : goto fail_printk;
280 1 : misc_class->devnode = misc_devnode;
281 1 : return 0;
282 :
283 0 : fail_printk:
284 0 : pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
285 0 : class_destroy(misc_class);
286 0 : fail_remove:
287 0 : if (ret)
288 0 : remove_proc_entry("misc", NULL);
289 : return err;
290 : }
291 : subsys_initcall(misc_init);
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