1/*
2 * CUSE: Character device in Userspace
3 *
4 * Copyright (C) 2008-2009  SUSE Linux Products GmbH
5 * Copyright (C) 2008-2009  Tejun Heo <tj@kernel.org>
6 *
7 * This file is released under the GPLv2.
8 *
9 * CUSE enables character devices to be implemented from userland much
10 * like FUSE allows filesystems.  On initialization /dev/cuse is
11 * created.  By opening the file and replying to the CUSE_INIT request
12 * userland CUSE server can create a character device.  After that the
13 * operation is very similar to FUSE.
14 *
15 * A CUSE instance involves the following objects.
16 *
17 * cuse_conn	: contains fuse_conn and serves as bonding structure
18 * channel	: file handle connected to the userland CUSE server
19 * cdev		: the implemented character device
20 * dev		: generic device for cdev
21 *
22 * Note that 'channel' is what 'dev' is in FUSE.  As CUSE deals with
23 * devices, it's called 'channel' to reduce confusion.
24 *
25 * channel determines when the character device dies.  When channel is
26 * closed, everything begins to destruct.  The cuse_conn is taken off
27 * the lookup table preventing further access from cdev, cdev and
28 * generic device are removed and the base reference of cuse_conn is
29 * put.
30 *
31 * On each open, the matching cuse_conn is looked up and if found an
32 * additional reference is taken which is released when the file is
33 * closed.
34 */
35
36#include <linux/fuse.h>
37#include <linux/cdev.h>
38#include <linux/device.h>
39#include <linux/file.h>
40#include <linux/fs.h>
41#include <linux/kdev_t.h>
42#include <linux/kthread.h>
43#include <linux/list.h>
44#include <linux/magic.h>
45#include <linux/miscdevice.h>
46#include <linux/mutex.h>
47#include <linux/slab.h>
48#include <linux/stat.h>
49#include <linux/module.h>
50#include <linux/uio.h>
51
52#include "fuse_i.h"
53
54#define CUSE_CONNTBL_LEN	64
55
56struct cuse_conn {
57	struct list_head	list;	/* linked on cuse_conntbl */
58	struct fuse_conn	fc;	/* fuse connection */
59	struct cdev		*cdev;	/* associated character device */
60	struct device		*dev;	/* device representing @cdev */
61
62	/* init parameters, set once during initialization */
63	bool			unrestricted_ioctl;
64};
65
66static DEFINE_MUTEX(cuse_lock);		/* protects registration */
67static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
68static struct class *cuse_class;
69
70static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
71{
72	return container_of(fc, struct cuse_conn, fc);
73}
74
75static struct list_head *cuse_conntbl_head(dev_t devt)
76{
77	return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
78}
79
80
81/**************************************************************************
82 * CUSE frontend operations
83 *
84 * These are file operations for the character device.
85 *
86 * On open, CUSE opens a file from the FUSE mnt and stores it to
87 * private_data of the open file.  All other ops call FUSE ops on the
88 * FUSE file.
89 */
90
91static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
92{
93	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
94	loff_t pos = 0;
95
96	return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
97}
98
99static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
100{
101	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
102	loff_t pos = 0;
103	/*
104	 * No locking or generic_write_checks(), the server is
105	 * responsible for locking and sanity checks.
106	 */
107	return fuse_direct_io(&io, from, &pos,
108			      FUSE_DIO_WRITE | FUSE_DIO_CUSE);
109}
110
111static int cuse_open(struct inode *inode, struct file *file)
112{
113	dev_t devt = inode->i_cdev->dev;
114	struct cuse_conn *cc = NULL, *pos;
115	int rc;
116
117	/* look up and get the connection */
118	mutex_lock(&cuse_lock);
119	list_for_each_entry(pos, cuse_conntbl_head(devt), list)
120		if (pos->dev->devt == devt) {
121			fuse_conn_get(&pos->fc);
122			cc = pos;
123			break;
124		}
125	mutex_unlock(&cuse_lock);
126
127	/* dead? */
128	if (!cc)
129		return -ENODEV;
130
131	/*
132	 * Generic permission check is already done against the chrdev
133	 * file, proceed to open.
134	 */
135	rc = fuse_do_open(&cc->fc, 0, file, 0);
136	if (rc)
137		fuse_conn_put(&cc->fc);
138	return rc;
139}
140
141static int cuse_release(struct inode *inode, struct file *file)
142{
143	struct fuse_file *ff = file->private_data;
144	struct fuse_conn *fc = ff->fc;
145
146	fuse_sync_release(ff, file->f_flags);
147	fuse_conn_put(fc);
148
149	return 0;
150}
151
152static long cuse_file_ioctl(struct file *file, unsigned int cmd,
153			    unsigned long arg)
154{
155	struct fuse_file *ff = file->private_data;
156	struct cuse_conn *cc = fc_to_cc(ff->fc);
157	unsigned int flags = 0;
158
159	if (cc->unrestricted_ioctl)
160		flags |= FUSE_IOCTL_UNRESTRICTED;
161
162	return fuse_do_ioctl(file, cmd, arg, flags);
163}
164
165static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
166				   unsigned long arg)
167{
168	struct fuse_file *ff = file->private_data;
169	struct cuse_conn *cc = fc_to_cc(ff->fc);
170	unsigned int flags = FUSE_IOCTL_COMPAT;
171
172	if (cc->unrestricted_ioctl)
173		flags |= FUSE_IOCTL_UNRESTRICTED;
174
175	return fuse_do_ioctl(file, cmd, arg, flags);
176}
177
178static const struct file_operations cuse_frontend_fops = {
179	.owner			= THIS_MODULE,
180	.read_iter		= cuse_read_iter,
181	.write_iter		= cuse_write_iter,
182	.open			= cuse_open,
183	.release		= cuse_release,
184	.unlocked_ioctl		= cuse_file_ioctl,
185	.compat_ioctl		= cuse_file_compat_ioctl,
186	.poll			= fuse_file_poll,
187	.llseek		= noop_llseek,
188};
189
190
191/**************************************************************************
192 * CUSE channel initialization and destruction
193 */
194
195struct cuse_devinfo {
196	const char		*name;
197};
198
199/**
200 * cuse_parse_one - parse one key=value pair
201 * @pp: i/o parameter for the current position
202 * @end: points to one past the end of the packed string
203 * @keyp: out parameter for key
204 * @valp: out parameter for value
205 *
206 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
207 * at @end - 1.  This function parses one pair and set *@keyp to the
208 * start of the key and *@valp to the start of the value.  Note that
209 * the original string is modified such that the key string is
210 * terminated with '\0'.  *@pp is updated to point to the next string.
211 *
212 * RETURNS:
213 * 1 on successful parse, 0 on EOF, -errno on failure.
214 */
215static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
216{
217	char *p = *pp;
218	char *key, *val;
219
220	while (p < end && *p == '\0')
221		p++;
222	if (p == end)
223		return 0;
224
225	if (end[-1] != '\0') {
226		printk(KERN_ERR "CUSE: info not properly terminated\n");
227		return -EINVAL;
228	}
229
230	key = val = p;
231	p += strlen(p);
232
233	if (valp) {
234		strsep(&val, "=");
235		if (!val)
236			val = key + strlen(key);
237		key = strstrip(key);
238		val = strstrip(val);
239	} else
240		key = strstrip(key);
241
242	if (!strlen(key)) {
243		printk(KERN_ERR "CUSE: zero length info key specified\n");
244		return -EINVAL;
245	}
246
247	*pp = p;
248	*keyp = key;
249	if (valp)
250		*valp = val;
251
252	return 1;
253}
254
255/**
256 * cuse_parse_dev_info - parse device info
257 * @p: device info string
258 * @len: length of device info string
259 * @devinfo: out parameter for parsed device info
260 *
261 * Parse @p to extract device info and store it into @devinfo.  String
262 * pointed to by @p is modified by parsing and @devinfo points into
263 * them, so @p shouldn't be freed while @devinfo is in use.
264 *
265 * RETURNS:
266 * 0 on success, -errno on failure.
267 */
268static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
269{
270	char *end = p + len;
271	char *uninitialized_var(key), *uninitialized_var(val);
272	int rc;
273
274	while (true) {
275		rc = cuse_parse_one(&p, end, &key, &val);
276		if (rc < 0)
277			return rc;
278		if (!rc)
279			break;
280		if (strcmp(key, "DEVNAME") == 0)
281			devinfo->name = val;
282		else
283			printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
284			       key);
285	}
286
287	if (!devinfo->name || !strlen(devinfo->name)) {
288		printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
289		return -EINVAL;
290	}
291
292	return 0;
293}
294
295static void cuse_gendev_release(struct device *dev)
296{
297	kfree(dev);
298}
299
300/**
301 * cuse_process_init_reply - finish initializing CUSE channel
302 *
303 * This function creates the character device and sets up all the
304 * required data structures for it.  Please read the comment at the
305 * top of this file for high level overview.
306 */
307static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
308{
309	struct cuse_conn *cc = fc_to_cc(fc), *pos;
310	struct cuse_init_out *arg = req->out.args[0].value;
311	struct page *page = req->pages[0];
312	struct cuse_devinfo devinfo = { };
313	struct device *dev;
314	struct cdev *cdev;
315	dev_t devt;
316	int rc, i;
317
318	if (req->out.h.error ||
319	    arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
320		goto err;
321	}
322
323	fc->minor = arg->minor;
324	fc->max_read = max_t(unsigned, arg->max_read, 4096);
325	fc->max_write = max_t(unsigned, arg->max_write, 4096);
326
327	/* parse init reply */
328	cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
329
330	rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
331				&devinfo);
332	if (rc)
333		goto err;
334
335	/* determine and reserve devt */
336	devt = MKDEV(arg->dev_major, arg->dev_minor);
337	if (!MAJOR(devt))
338		rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
339	else
340		rc = register_chrdev_region(devt, 1, devinfo.name);
341	if (rc) {
342		printk(KERN_ERR "CUSE: failed to register chrdev region\n");
343		goto err;
344	}
345
346	/* devt determined, create device */
347	rc = -ENOMEM;
348	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
349	if (!dev)
350		goto err_region;
351
352	device_initialize(dev);
353	dev_set_uevent_suppress(dev, 1);
354	dev->class = cuse_class;
355	dev->devt = devt;
356	dev->release = cuse_gendev_release;
357	dev_set_drvdata(dev, cc);
358	dev_set_name(dev, "%s", devinfo.name);
359
360	mutex_lock(&cuse_lock);
361
362	/* make sure the device-name is unique */
363	for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
364		list_for_each_entry(pos, &cuse_conntbl[i], list)
365			if (!strcmp(dev_name(pos->dev), dev_name(dev)))
366				goto err_unlock;
367	}
368
369	rc = device_add(dev);
370	if (rc)
371		goto err_unlock;
372
373	/* register cdev */
374	rc = -ENOMEM;
375	cdev = cdev_alloc();
376	if (!cdev)
377		goto err_unlock;
378
379	cdev->owner = THIS_MODULE;
380	cdev->ops = &cuse_frontend_fops;
381
382	rc = cdev_add(cdev, devt, 1);
383	if (rc)
384		goto err_cdev;
385
386	cc->dev = dev;
387	cc->cdev = cdev;
388
389	/* make the device available */
390	list_add(&cc->list, cuse_conntbl_head(devt));
391	mutex_unlock(&cuse_lock);
392
393	/* announce device availability */
394	dev_set_uevent_suppress(dev, 0);
395	kobject_uevent(&dev->kobj, KOBJ_ADD);
396out:
397	kfree(arg);
398	__free_page(page);
399	return;
400
401err_cdev:
402	cdev_del(cdev);
403err_unlock:
404	mutex_unlock(&cuse_lock);
405	put_device(dev);
406err_region:
407	unregister_chrdev_region(devt, 1);
408err:
409	fuse_abort_conn(fc);
410	goto out;
411}
412
413static int cuse_send_init(struct cuse_conn *cc)
414{
415	int rc;
416	struct fuse_req *req;
417	struct page *page;
418	struct fuse_conn *fc = &cc->fc;
419	struct cuse_init_in *arg;
420	void *outarg;
421
422	BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
423
424	req = fuse_get_req_for_background(fc, 1);
425	if (IS_ERR(req)) {
426		rc = PTR_ERR(req);
427		goto err;
428	}
429
430	rc = -ENOMEM;
431	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
432	if (!page)
433		goto err_put_req;
434
435	outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL);
436	if (!outarg)
437		goto err_free_page;
438
439	arg = &req->misc.cuse_init_in;
440	arg->major = FUSE_KERNEL_VERSION;
441	arg->minor = FUSE_KERNEL_MINOR_VERSION;
442	arg->flags |= CUSE_UNRESTRICTED_IOCTL;
443	req->in.h.opcode = CUSE_INIT;
444	req->in.numargs = 1;
445	req->in.args[0].size = sizeof(struct cuse_init_in);
446	req->in.args[0].value = arg;
447	req->out.numargs = 2;
448	req->out.args[0].size = sizeof(struct cuse_init_out);
449	req->out.args[0].value = outarg;
450	req->out.args[1].size = CUSE_INIT_INFO_MAX;
451	req->out.argvar = 1;
452	req->out.argpages = 1;
453	req->pages[0] = page;
454	req->page_descs[0].length = req->out.args[1].size;
455	req->num_pages = 1;
456	req->end = cuse_process_init_reply;
457	fuse_request_send_background(fc, req);
458
459	return 0;
460
461err_free_page:
462	__free_page(page);
463err_put_req:
464	fuse_put_request(fc, req);
465err:
466	return rc;
467}
468
469static void cuse_fc_release(struct fuse_conn *fc)
470{
471	struct cuse_conn *cc = fc_to_cc(fc);
472	kfree_rcu(cc, fc.rcu);
473}
474
475/**
476 * cuse_channel_open - open method for /dev/cuse
477 * @inode: inode for /dev/cuse
478 * @file: file struct being opened
479 *
480 * Userland CUSE server can create a CUSE device by opening /dev/cuse
481 * and replying to the initialization request kernel sends.  This
482 * function is responsible for handling CUSE device initialization.
483 * Because the fd opened by this function is used during
484 * initialization, this function only creates cuse_conn and sends
485 * init.  The rest is delegated to a kthread.
486 *
487 * RETURNS:
488 * 0 on success, -errno on failure.
489 */
490static int cuse_channel_open(struct inode *inode, struct file *file)
491{
492	struct cuse_conn *cc;
493	int rc;
494
495	/* set up cuse_conn */
496	cc = kzalloc(sizeof(*cc), GFP_KERNEL);
497	if (!cc)
498		return -ENOMEM;
499
500	fuse_conn_init(&cc->fc);
501
502	INIT_LIST_HEAD(&cc->list);
503	cc->fc.release = cuse_fc_release;
504
505	cc->fc.connected = 1;
506	cc->fc.initialized = 1;
507	rc = cuse_send_init(cc);
508	if (rc) {
509		fuse_conn_put(&cc->fc);
510		return rc;
511	}
512	file->private_data = &cc->fc;	/* channel owns base reference to cc */
513
514	return 0;
515}
516
517/**
518 * cuse_channel_release - release method for /dev/cuse
519 * @inode: inode for /dev/cuse
520 * @file: file struct being closed
521 *
522 * Disconnect the channel, deregister CUSE device and initiate
523 * destruction by putting the default reference.
524 *
525 * RETURNS:
526 * 0 on success, -errno on failure.
527 */
528static int cuse_channel_release(struct inode *inode, struct file *file)
529{
530	struct cuse_conn *cc = fc_to_cc(file->private_data);
531	int rc;
532
533	/* remove from the conntbl, no more access from this point on */
534	mutex_lock(&cuse_lock);
535	list_del_init(&cc->list);
536	mutex_unlock(&cuse_lock);
537
538	/* remove device */
539	if (cc->dev)
540		device_unregister(cc->dev);
541	if (cc->cdev) {
542		unregister_chrdev_region(cc->cdev->dev, 1);
543		cdev_del(cc->cdev);
544	}
545
546	rc = fuse_dev_release(inode, file);	/* puts the base reference */
547
548	return rc;
549}
550
551static struct file_operations cuse_channel_fops; /* initialized during init */
552
553
554/**************************************************************************
555 * Misc stuff and module initializatiion
556 *
557 * CUSE exports the same set of attributes to sysfs as fusectl.
558 */
559
560static ssize_t cuse_class_waiting_show(struct device *dev,
561				       struct device_attribute *attr, char *buf)
562{
563	struct cuse_conn *cc = dev_get_drvdata(dev);
564
565	return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
566}
567static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);
568
569static ssize_t cuse_class_abort_store(struct device *dev,
570				      struct device_attribute *attr,
571				      const char *buf, size_t count)
572{
573	struct cuse_conn *cc = dev_get_drvdata(dev);
574
575	fuse_abort_conn(&cc->fc);
576	return count;
577}
578static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
579
580static struct attribute *cuse_class_dev_attrs[] = {
581	&dev_attr_waiting.attr,
582	&dev_attr_abort.attr,
583	NULL,
584};
585ATTRIBUTE_GROUPS(cuse_class_dev);
586
587static struct miscdevice cuse_miscdev = {
588	.minor		= CUSE_MINOR,
589	.name		= "cuse",
590	.fops		= &cuse_channel_fops,
591};
592
593MODULE_ALIAS_MISCDEV(CUSE_MINOR);
594MODULE_ALIAS("devname:cuse");
595
596static int __init cuse_init(void)
597{
598	int i, rc;
599
600	/* init conntbl */
601	for (i = 0; i < CUSE_CONNTBL_LEN; i++)
602		INIT_LIST_HEAD(&cuse_conntbl[i]);
603
604	/* inherit and extend fuse_dev_operations */
605	cuse_channel_fops		= fuse_dev_operations;
606	cuse_channel_fops.owner		= THIS_MODULE;
607	cuse_channel_fops.open		= cuse_channel_open;
608	cuse_channel_fops.release	= cuse_channel_release;
609
610	cuse_class = class_create(THIS_MODULE, "cuse");
611	if (IS_ERR(cuse_class))
612		return PTR_ERR(cuse_class);
613
614	cuse_class->dev_groups = cuse_class_dev_groups;
615
616	rc = misc_register(&cuse_miscdev);
617	if (rc) {
618		class_destroy(cuse_class);
619		return rc;
620	}
621
622	return 0;
623}
624
625static void __exit cuse_exit(void)
626{
627	misc_deregister(&cuse_miscdev);
628	class_destroy(cuse_class);
629}
630
631module_init(cuse_init);
632module_exit(cuse_exit);
633
634MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
635MODULE_DESCRIPTION("Character device in Userspace");
636MODULE_LICENSE("GPL");
637