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