misc.c

  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.
 62 */
 63static DEFINE_IDA(misc_minors_ida);
 64
 65static 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
 79static void misc_minor_free(int minor)
 80{
 81	ida_free(&misc_minors_ida, minor);
 82}
 83
 84#ifdef CONFIG_PROC_FS
 85static 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
 91static 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
 96static void misc_seq_stop(struct seq_file *seq, void *v)
 97{
 98	mutex_unlock(&misc_mtx);
 99}
100
101static 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
110static 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
118static 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	/* Only request module for fixed minor code */
136	if (!new_fops && minor < MISC_DYNAMIC_MINOR) {
137		mutex_unlock(&misc_mtx);
138		request_module("char-major-%d-%d", MISC_MAJOR, minor);
139		mutex_lock(&misc_mtx);
140
141		list_for_each_entry(iter, &misc_list, list) {
142			if (iter->minor != minor)
143				continue;
144			c = iter;
145			new_fops = fops_get(iter->fops);
146			break;
147		}
148	}
149
150	if (!new_fops)
151		goto fail;
152
153	/*
154	 * Place the miscdevice in the file's
155	 * private_data so it can be used by the
156	 * file operations, including f_op->open below
157	 */
158	file->private_data = c;
159
160	err = 0;
161	replace_fops(file, new_fops);
162	if (file->f_op->open)
163		err = file->f_op->open(inode, file);
164fail:
165	mutex_unlock(&misc_mtx);
166	return err;
167}
168
169static char *misc_devnode(const struct device *dev, umode_t *mode)
170{
171	const struct miscdevice *c = dev_get_drvdata(dev);
172
173	if (mode && c->mode)
174		*mode = c->mode;
175	if (c->nodename)
176		return kstrdup(c->nodename, GFP_KERNEL);
177	return NULL;
178}
179
180static const struct class misc_class = {
181	.name		= "misc",
182	.devnode	= misc_devnode,
183};
184
185static const struct file_operations misc_fops = {
186	.owner		= THIS_MODULE,
187	.open		= misc_open,
188	.llseek		= noop_llseek,
189};
190
191/**
192 *	misc_register	-	register a miscellaneous device
193 *	@misc: device structure
194 *
195 *	Register a miscellaneous device with the kernel. If the minor
196 *	number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
197 *	and placed in the minor field of the structure. For other cases
198 *	the minor number requested is used.
199 *
200 *	The structure passed is linked into the kernel and may not be
201 *	destroyed until it has been unregistered. By default, an open()
202 *	syscall to the device sets file->private_data to point to the
203 *	structure. Drivers don't need open in fops for this.
204 *
205 *	A zero is returned on success and a negative errno code for
206 *	failure.
207 */
208
209int misc_register(struct miscdevice *misc)
210{
211	dev_t dev;
212	int err = 0;
213	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
214
215	if (misc->minor > MISC_DYNAMIC_MINOR) {
216		pr_err("Invalid fixed minor %d for miscdevice '%s'\n",
217		       misc->minor, misc->name);
218		return -EINVAL;
219	}
220
221	INIT_LIST_HEAD(&misc->list);
222
223	mutex_lock(&misc_mtx);
224
225	if (is_dynamic) {
226		int i = misc_minor_alloc(misc->minor);
227
228		if (i < 0) {
229			err = -EBUSY;
230			goto out;
231		}
232		misc->minor = i;
233	} else {
234		struct miscdevice *c;
235		int i;
236
237		list_for_each_entry(c, &misc_list, list) {
238			if (c->minor == misc->minor) {
239				err = -EBUSY;
240				goto out;
241			}
242		}
243
244		i = misc_minor_alloc(misc->minor);
245		if (i < 0) {
246			err = -EBUSY;
247			goto out;
248		}
249	}
250
251	dev = MKDEV(MISC_MAJOR, misc->minor);
252
253	misc->this_device =
254		device_create_with_groups(&misc_class, misc->parent, dev,
255					  misc, misc->groups, "%s", misc->name);
256	if (IS_ERR(misc->this_device)) {
257		misc_minor_free(misc->minor);
258		if (is_dynamic) {
259			misc->minor = MISC_DYNAMIC_MINOR;
260		}
261		err = PTR_ERR(misc->this_device);
262		goto out;
263	}
264
265	/*
266	 * Add it to the front, so that later devices can "override"
267	 * earlier defaults
268	 */
269	list_add(&misc->list, &misc_list);
270 out:
271	mutex_unlock(&misc_mtx);
272	return err;
273}
274EXPORT_SYMBOL(misc_register);
275
276/**
277 *	misc_deregister - unregister a miscellaneous device
278 *	@misc: device to unregister
279 *
280 *	Unregister a miscellaneous device that was previously
281 *	successfully registered with misc_register().
282 */
283
284void misc_deregister(struct miscdevice *misc)
285{
286	mutex_lock(&misc_mtx);
287	list_del_init(&misc->list);
288	device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
289	misc_minor_free(misc->minor);
290	if (misc->minor > MISC_DYNAMIC_MINOR)
291		misc->minor = MISC_DYNAMIC_MINOR;
292	mutex_unlock(&misc_mtx);
293}
294EXPORT_SYMBOL(misc_deregister);
295
296static int __init misc_init(void)
297{
298	int err;
299	struct proc_dir_entry *misc_proc_file;
300
301	misc_proc_file = proc_create_seq("misc", 0, NULL, &misc_seq_ops);
302	err = class_register(&misc_class);
303	if (err)
304		goto fail_remove;
305
306	err = __register_chrdev(MISC_MAJOR, 0, MINORMASK + 1, "misc", &misc_fops);
307	if (err < 0)
308		goto fail_printk;
309	return 0;
310
311fail_printk:
312	pr_err("unable to get major %d for misc devices\n", MISC_MAJOR);
313	class_unregister(&misc_class);
314fail_remove:
315	if (misc_proc_file)
316		remove_proc_entry("misc", NULL);
317	return err;
318}
319subsys_initcall(misc_init);