raw.c revision b1dd3b2843b3b73b7fc2ee47d96310cd1c051371 
1/*
2 * linux/drivers/char/raw.c
3 *
4 * Front-end raw character devices.  These can be bound to any block
5 * devices to provide genuine Unix raw character device semantics.
6 *
7 * We reserve minor number 0 for a control interface.  ioctl()s on this
8 * device are used to bind the other minor numbers to block devices.
9 */
10
11#include <linux/init.h>
12#include <linux/fs.h>
13#include <linux/major.h>
14#include <linux/blkdev.h>
15#include <linux/module.h>
16#include <linux/raw.h>
17#include <linux/capability.h>
18#include <linux/uio.h>
19#include <linux/cdev.h>
20#include <linux/device.h>
21#include <linux/mutex.h>
22#include <linux/smp_lock.h>
23#include <linux/gfp.h>
24
25#include <asm/uaccess.h>
26
27struct raw_device_data {
28	struct block_device *binding;
29	int inuse;
30};
31
32static struct class *raw_class;
33static struct raw_device_data raw_devices[MAX_RAW_MINORS];
34static DEFINE_MUTEX(raw_mutex);
35static const struct file_operations raw_ctl_fops; /* forward declaration */
36
37/*
38 * Open/close code for raw IO.
39 *
40 * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
41 * point at the blockdev's address_space and set the file handle to use
42 * O_DIRECT.
43 *
44 * Set the device's soft blocksize to the minimum possible.  This gives the
45 * finest possible alignment and has no adverse impact on performance.
46 */
47static int raw_open(struct inode *inode, struct file *filp)
48{
49	const int minor = iminor(inode);
50	struct block_device *bdev;
51	int err;
52
53	if (minor == 0) {	/* It is the control device */
54		filp->f_op = &raw_ctl_fops;
55		return 0;
56	}
57
58	lock_kernel();
59	mutex_lock(&raw_mutex);
60
61	/*
62	 * All we need to do on open is check that the device is bound.
63	 */
64	bdev = raw_devices[minor].binding;
65	err = -ENODEV;
66	if (!bdev)
67		goto out;
68	igrab(bdev->bd_inode);
69	err = blkdev_get(bdev, filp->f_mode);
70	if (err)
71		goto out;
72	err = bd_claim(bdev, raw_open);
73	if (err)
74		goto out1;
75	err = set_blocksize(bdev, bdev_logical_block_size(bdev));
76	if (err)
77		goto out2;
78	filp->f_flags |= O_DIRECT;
79	filp->f_mapping = bdev->bd_inode->i_mapping;
80	if (++raw_devices[minor].inuse == 1)
81		filp->f_path.dentry->d_inode->i_mapping =
82			bdev->bd_inode->i_mapping;
83	filp->private_data = bdev;
84	mutex_unlock(&raw_mutex);
85	unlock_kernel();
86	return 0;
87
88out2:
89	bd_release(bdev);
90out1:
91	blkdev_put(bdev, filp->f_mode);
92out:
93	mutex_unlock(&raw_mutex);
94	unlock_kernel();
95	return err;
96}
97
98/*
99 * When the final fd which refers to this character-special node is closed, we
100 * make its ->mapping point back at its own i_data.
101 */
102static int raw_release(struct inode *inode, struct file *filp)
103{
104	const int minor= iminor(inode);
105	struct block_device *bdev;
106
107	mutex_lock(&raw_mutex);
108	bdev = raw_devices[minor].binding;
109	if (--raw_devices[minor].inuse == 0) {
110		/* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
111		inode->i_mapping = &inode->i_data;
112		inode->i_mapping->backing_dev_info = &default_backing_dev_info;
113	}
114	mutex_unlock(&raw_mutex);
115
116	bd_release(bdev);
117	blkdev_put(bdev, filp->f_mode);
118	return 0;
119}
120
121/*
122 * Forward ioctls to the underlying block device.
123 */
124static int
125raw_ioctl(struct inode *inode, struct file *filp,
126		  unsigned int command, unsigned long arg)
127{
128	struct block_device *bdev = filp->private_data;
129
130	return blkdev_ioctl(bdev, 0, command, arg);
131}
132
133static void bind_device(struct raw_config_request *rq)
134{
135	device_destroy(raw_class, MKDEV(RAW_MAJOR, rq->raw_minor));
136	device_create(raw_class, NULL, MKDEV(RAW_MAJOR, rq->raw_minor), NULL,
137		      "raw%d", rq->raw_minor);
138}
139
140/*
141 * Deal with ioctls against the raw-device control interface, to bind
142 * and unbind other raw devices.
143 */
144static int raw_ctl_ioctl(struct inode *inode, struct file *filp,
145			unsigned int command, unsigned long arg)
146{
147	struct raw_config_request rq;
148	struct raw_device_data *rawdev;
149	int err = 0;
150
151	switch (command) {
152	case RAW_SETBIND:
153	case RAW_GETBIND:
154
155		/* First, find out which raw minor we want */
156
157		if (copy_from_user(&rq, (void __user *) arg, sizeof(rq))) {
158			err = -EFAULT;
159			goto out;
160		}
161
162		if (rq.raw_minor <= 0 || rq.raw_minor >= MAX_RAW_MINORS) {
163			err = -EINVAL;
164			goto out;
165		}
166		rawdev = &raw_devices[rq.raw_minor];
167
168		if (command == RAW_SETBIND) {
169			dev_t dev;
170
171			/*
172			 * This is like making block devices, so demand the
173			 * same capability
174			 */
175			if (!capable(CAP_SYS_ADMIN)) {
176				err = -EPERM;
177				goto out;
178			}
179
180			/*
181			 * For now, we don't need to check that the underlying
182			 * block device is present or not: we can do that when
183			 * the raw device is opened.  Just check that the
184			 * major/minor numbers make sense.
185			 */
186
187			dev = MKDEV(rq.block_major, rq.block_minor);
188			if ((rq.block_major == 0 && rq.block_minor != 0) ||
189					MAJOR(dev) != rq.block_major ||
190					MINOR(dev) != rq.block_minor) {
191				err = -EINVAL;
192				goto out;
193			}
194
195			mutex_lock(&raw_mutex);
196			if (rawdev->inuse) {
197				mutex_unlock(&raw_mutex);
198				err = -EBUSY;
199				goto out;
200			}
201			if (rawdev->binding) {
202				bdput(rawdev->binding);
203				module_put(THIS_MODULE);
204			}
205			if (rq.block_major == 0 && rq.block_minor == 0) {
206				/* unbind */
207				rawdev->binding = NULL;
208				device_destroy(raw_class,
209						MKDEV(RAW_MAJOR, rq.raw_minor));
210			} else {
211				rawdev->binding = bdget(dev);
212				if (rawdev->binding == NULL)
213					err = -ENOMEM;
214				else {
215					__module_get(THIS_MODULE);
216					bind_device(&rq);
217				}
218			}
219			mutex_unlock(&raw_mutex);
220		} else {
221			struct block_device *bdev;
222
223			mutex_lock(&raw_mutex);
224			bdev = rawdev->binding;
225			if (bdev) {
226				rq.block_major = MAJOR(bdev->bd_dev);
227				rq.block_minor = MINOR(bdev->bd_dev);
228			} else {
229				rq.block_major = rq.block_minor = 0;
230			}
231			mutex_unlock(&raw_mutex);
232			if (copy_to_user((void __user *)arg, &rq, sizeof(rq))) {
233				err = -EFAULT;
234				goto out;
235			}
236		}
237		break;
238	default:
239		err = -EINVAL;
240		break;
241	}
242out:
243	return err;
244}
245
246static const struct file_operations raw_fops = {
247	.read	=	do_sync_read,
248	.aio_read = 	generic_file_aio_read,
249	.write	=	do_sync_write,
250	.aio_write =	blkdev_aio_write,
251	.fsync	=	blkdev_fsync,
252	.open	=	raw_open,
253	.release=	raw_release,
254	.ioctl	=	raw_ioctl,
255	.owner	=	THIS_MODULE,
256};
257
258static const struct file_operations raw_ctl_fops = {
259	.ioctl	=	raw_ctl_ioctl,
260	.open	=	raw_open,
261	.owner	=	THIS_MODULE,
262};
263
264static struct cdev raw_cdev;
265
266static char *raw_devnode(struct device *dev, mode_t *mode)
267{
268	return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
269}
270
271static int __init raw_init(void)
272{
273	dev_t dev = MKDEV(RAW_MAJOR, 0);
274	int ret;
275
276	ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
277	if (ret)
278		goto error;
279
280	cdev_init(&raw_cdev, &raw_fops);
281	ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
282	if (ret) {
283		kobject_put(&raw_cdev.kobj);
284		goto error_region;
285	}
286
287	raw_class = class_create(THIS_MODULE, "raw");
288	if (IS_ERR(raw_class)) {
289		printk(KERN_ERR "Error creating raw class.\n");
290		cdev_del(&raw_cdev);
291		ret = PTR_ERR(raw_class);
292		goto error_region;
293	}
294	raw_class->devnode = raw_devnode;
295	device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
296
297	return 0;
298
299error_region:
300	unregister_chrdev_region(dev, MAX_RAW_MINORS);
301error:
302	return ret;
303}
304
305static void __exit raw_exit(void)
306{
307	device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
308	class_destroy(raw_class);
309	cdev_del(&raw_cdev);
310	unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
311}
312
313module_init(raw_init);
314module_exit(raw_exit);
315MODULE_LICENSE("GPL");
316