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 */
57static LIST_HEAD(misc_list);
58static DEFINE_MUTEX(misc_mtx);
59
60/*
61 * Assigned numbers, used for dynamic minors
62 */
63#define DYNAMIC_MINORS 128 /* like dynamic majors */
64static DEFINE_IDA(misc_minors_ida);
65
66static 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
80static 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
89static 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
95static 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
100static void misc_seq_stop(struct seq_file *seq, void *v)
101{
102	mutex_unlock(&misc_mtx);
103}
104
105static 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
114static 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
122static 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);
166fail:
167	mutex_unlock(&misc_mtx);
168	return err;
169}
170
171static 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
182static const struct class misc_class = {
183	.name		= "misc",
184	.devnode	= misc_devnode,
185};
186
187static 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
211int 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}
263EXPORT_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
273void 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}
284EXPORT_SYMBOL(misc_deregister);
285
286static 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
301fail_printk:
302	pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
303	class_unregister(&misc_class);
304fail_remove:
305	if (ret)
306		remove_proc_entry("misc", NULL);
307	return err;
308}
309subsys_initcall(misc_init);
310