2 * CUSE: Character device in Userspace
4 * Copyright (C) 2008-2009 SUSE Linux Products GmbH
5 * Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
7 * This file is released under the GPLv2.
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.
15 * A CUSE instance involves the following objects.
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
22 * Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with
23 * devices, it's called 'channel' to reduce confusion.
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
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
36 #include <linux/fuse.h>
37 #include <linux/cdev.h>
38 #include <linux/device.h>
39 #include <linux/file.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>
53 #define CUSE_CONNTBL_LEN 64
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 */
61 /* init parameters, set once during initialization */
62 bool unrestricted_ioctl;
65 static DEFINE_MUTEX(cuse_lock); /* protects registration */
66 static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
67 static struct class *cuse_class;
69 static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
71 return container_of(fc, struct cuse_conn, fc);
74 static struct list_head *cuse_conntbl_head(dev_t devt)
76 return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
80 /**************************************************************************
81 * CUSE frontend operations
83 * These are file operations for the character device.
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
90 static ssize_t cuse_read(struct file *file, char __user *buf, size_t count,
94 struct iovec iov = { .iov_base = buf, .iov_len = count };
95 struct fuse_io_priv io = { .async = 0, .file = file };
97 return fuse_direct_io(&io, &iov, 1, count, &pos, 0);
100 static ssize_t cuse_write(struct file *file, const char __user *buf,
101 size_t count, loff_t *ppos)
104 struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = count };
105 struct fuse_io_priv io = { .async = 0, .file = file };
108 * No locking or generic_write_checks(), the server is
109 * responsible for locking and sanity checks.
111 return fuse_direct_io(&io, &iov, 1, count, &pos, 1);
114 static int cuse_open(struct inode *inode, struct file *file)
116 dev_t devt = inode->i_cdev->dev;
117 struct cuse_conn *cc = NULL, *pos;
120 /* look up and get the connection */
121 mutex_lock(&cuse_lock);
122 list_for_each_entry(pos, cuse_conntbl_head(devt), list)
123 if (pos->dev->devt == devt) {
124 fuse_conn_get(&pos->fc);
128 mutex_unlock(&cuse_lock);
135 * Generic permission check is already done against the chrdev
136 * file, proceed to open.
138 rc = fuse_do_open(&cc->fc, 0, file, 0);
140 fuse_conn_put(&cc->fc);
144 static int cuse_release(struct inode *inode, struct file *file)
146 struct fuse_file *ff = file->private_data;
147 struct fuse_conn *fc = ff->fc;
149 fuse_sync_release(ff, file->f_flags);
155 static long cuse_file_ioctl(struct file *file, unsigned int cmd,
158 struct fuse_file *ff = file->private_data;
159 struct cuse_conn *cc = fc_to_cc(ff->fc);
160 unsigned int flags = 0;
162 if (cc->unrestricted_ioctl)
163 flags |= FUSE_IOCTL_UNRESTRICTED;
165 return fuse_do_ioctl(file, cmd, arg, flags);
168 static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
171 struct fuse_file *ff = file->private_data;
172 struct cuse_conn *cc = fc_to_cc(ff->fc);
173 unsigned int flags = FUSE_IOCTL_COMPAT;
175 if (cc->unrestricted_ioctl)
176 flags |= FUSE_IOCTL_UNRESTRICTED;
178 return fuse_do_ioctl(file, cmd, arg, flags);
181 static const struct file_operations cuse_frontend_fops = {
182 .owner = THIS_MODULE,
186 .release = cuse_release,
187 .unlocked_ioctl = cuse_file_ioctl,
188 .compat_ioctl = cuse_file_compat_ioctl,
189 .poll = fuse_file_poll,
190 .llseek = noop_llseek,
194 /**************************************************************************
195 * CUSE channel initialization and destruction
198 struct cuse_devinfo {
203 * cuse_parse_one - parse one key=value pair
204 * @pp: i/o parameter for the current position
205 * @end: points to one past the end of the packed string
206 * @keyp: out parameter for key
207 * @valp: out parameter for value
209 * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
210 * at @end - 1. This function parses one pair and set *@keyp to the
211 * start of the key and *@valp to the start of the value. Note that
212 * the original string is modified such that the key string is
213 * terminated with '\0'. *@pp is updated to point to the next string.
216 * 1 on successful parse, 0 on EOF, -errno on failure.
218 static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
223 while (p < end && *p == '\0')
228 if (end[-1] != '\0') {
229 printk(KERN_ERR "CUSE: info not properly terminated\n");
239 val = key + strlen(key);
246 printk(KERN_ERR "CUSE: zero length info key specified\n");
259 * cuse_parse_dev_info - parse device info
260 * @p: device info string
261 * @len: length of device info string
262 * @devinfo: out parameter for parsed device info
264 * Parse @p to extract device info and store it into @devinfo. String
265 * pointed to by @p is modified by parsing and @devinfo points into
266 * them, so @p shouldn't be freed while @devinfo is in use.
269 * 0 on success, -errno on failure.
271 static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
274 char *uninitialized_var(key), *uninitialized_var(val);
278 rc = cuse_parse_one(&p, end, &key, &val);
283 if (strcmp(key, "DEVNAME") == 0)
286 printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
290 if (!devinfo->name || !strlen(devinfo->name)) {
291 printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
298 static void cuse_gendev_release(struct device *dev)
304 * cuse_process_init_reply - finish initializing CUSE channel
306 * This function creates the character device and sets up all the
307 * required data structures for it. Please read the comment at the
308 * top of this file for high level overview.
310 static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
312 struct cuse_conn *cc = fc_to_cc(fc), *pos;
313 struct cuse_init_out *arg = req->out.args[0].value;
314 struct page *page = req->pages[0];
315 struct cuse_devinfo devinfo = { };
321 if (req->out.h.error ||
322 arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
326 fc->minor = arg->minor;
327 fc->max_read = max_t(unsigned, arg->max_read, 4096);
328 fc->max_write = max_t(unsigned, arg->max_write, 4096);
330 /* parse init reply */
331 cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
333 rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
338 /* determine and reserve devt */
339 devt = MKDEV(arg->dev_major, arg->dev_minor);
341 rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
343 rc = register_chrdev_region(devt, 1, devinfo.name);
345 printk(KERN_ERR "CUSE: failed to register chrdev region\n");
349 /* devt determined, create device */
351 dev = kzalloc(sizeof(*dev), GFP_KERNEL);
355 device_initialize(dev);
356 dev_set_uevent_suppress(dev, 1);
357 dev->class = cuse_class;
359 dev->release = cuse_gendev_release;
360 dev_set_drvdata(dev, cc);
361 dev_set_name(dev, "%s", devinfo.name);
363 mutex_lock(&cuse_lock);
365 /* make sure the device-name is unique */
366 for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
367 list_for_each_entry(pos, &cuse_conntbl[i], list)
368 if (!strcmp(dev_name(pos->dev), dev_name(dev)))
372 rc = device_add(dev);
382 cdev->owner = THIS_MODULE;
383 cdev->ops = &cuse_frontend_fops;
385 rc = cdev_add(cdev, devt, 1);
392 /* make the device available */
393 list_add(&cc->list, cuse_conntbl_head(devt));
394 mutex_unlock(&cuse_lock);
396 /* announce device availability */
397 dev_set_uevent_suppress(dev, 0);
398 kobject_uevent(&dev->kobj, KOBJ_ADD);
407 mutex_unlock(&cuse_lock);
410 unregister_chrdev_region(devt, 1);
416 static int cuse_send_init(struct cuse_conn *cc)
419 struct fuse_req *req;
421 struct fuse_conn *fc = &cc->fc;
422 struct cuse_init_in *arg;
425 BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
427 req = fuse_get_req_for_background(fc, 1);
434 page = alloc_page(GFP_KERNEL | __GFP_ZERO);
438 outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL);
442 arg = &req->misc.cuse_init_in;
443 arg->major = FUSE_KERNEL_VERSION;
444 arg->minor = FUSE_KERNEL_MINOR_VERSION;
445 arg->flags |= CUSE_UNRESTRICTED_IOCTL;
446 req->in.h.opcode = CUSE_INIT;
448 req->in.args[0].size = sizeof(struct cuse_init_in);
449 req->in.args[0].value = arg;
450 req->out.numargs = 2;
451 req->out.args[0].size = sizeof(struct cuse_init_out);
452 req->out.args[0].value = outarg;
453 req->out.args[1].size = CUSE_INIT_INFO_MAX;
455 req->out.argpages = 1;
456 req->pages[0] = page;
457 req->page_descs[0].length = req->out.args[1].size;
459 req->end = cuse_process_init_reply;
460 fuse_request_send_background(fc, req);
467 fuse_put_request(fc, req);
472 static void cuse_fc_release(struct fuse_conn *fc)
474 struct cuse_conn *cc = fc_to_cc(fc);
479 * cuse_channel_open - open method for /dev/cuse
480 * @inode: inode for /dev/cuse
481 * @file: file struct being opened
483 * Userland CUSE server can create a CUSE device by opening /dev/cuse
484 * and replying to the initialization request kernel sends. This
485 * function is responsible for handling CUSE device initialization.
486 * Because the fd opened by this function is used during
487 * initialization, this function only creates cuse_conn and sends
488 * init. The rest is delegated to a kthread.
491 * 0 on success, -errno on failure.
493 static int cuse_channel_open(struct inode *inode, struct file *file)
495 struct cuse_conn *cc;
498 /* set up cuse_conn */
499 cc = kzalloc(sizeof(*cc), GFP_KERNEL);
503 fuse_conn_init(&cc->fc);
505 INIT_LIST_HEAD(&cc->list);
506 cc->fc.release = cuse_fc_release;
508 cc->fc.connected = 1;
509 cc->fc.initialized = 1;
510 rc = cuse_send_init(cc);
512 fuse_conn_put(&cc->fc);
515 file->private_data = &cc->fc; /* channel owns base reference to cc */
521 * cuse_channel_release - release method for /dev/cuse
522 * @inode: inode for /dev/cuse
523 * @file: file struct being closed
525 * Disconnect the channel, deregister CUSE device and initiate
526 * destruction by putting the default reference.
529 * 0 on success, -errno on failure.
531 static int cuse_channel_release(struct inode *inode, struct file *file)
533 struct cuse_conn *cc = fc_to_cc(file->private_data);
536 /* remove from the conntbl, no more access from this point on */
537 mutex_lock(&cuse_lock);
538 list_del_init(&cc->list);
539 mutex_unlock(&cuse_lock);
543 device_unregister(cc->dev);
545 unregister_chrdev_region(cc->cdev->dev, 1);
549 rc = fuse_dev_release(inode, file); /* puts the base reference */
554 static struct file_operations cuse_channel_fops; /* initialized during init */
557 /**************************************************************************
558 * Misc stuff and module initializatiion
560 * CUSE exports the same set of attributes to sysfs as fusectl.
563 static ssize_t cuse_class_waiting_show(struct device *dev,
564 struct device_attribute *attr, char *buf)
566 struct cuse_conn *cc = dev_get_drvdata(dev);
568 return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
571 static ssize_t cuse_class_abort_store(struct device *dev,
572 struct device_attribute *attr,
573 const char *buf, size_t count)
575 struct cuse_conn *cc = dev_get_drvdata(dev);
577 fuse_abort_conn(&cc->fc);
581 static struct device_attribute cuse_class_dev_attrs[] = {
582 __ATTR(waiting, S_IFREG | 0400, cuse_class_waiting_show, NULL),
583 __ATTR(abort, S_IFREG | 0200, NULL, cuse_class_abort_store),
587 static struct miscdevice cuse_miscdev = {
588 .minor = MISC_DYNAMIC_MINOR,
590 .fops = &cuse_channel_fops,
593 static int __init cuse_init(void)
598 for (i = 0; i < CUSE_CONNTBL_LEN; i++)
599 INIT_LIST_HEAD(&cuse_conntbl[i]);
601 /* inherit and extend fuse_dev_operations */
602 cuse_channel_fops = fuse_dev_operations;
603 cuse_channel_fops.owner = THIS_MODULE;
604 cuse_channel_fops.open = cuse_channel_open;
605 cuse_channel_fops.release = cuse_channel_release;
607 cuse_class = class_create(THIS_MODULE, "cuse");
608 if (IS_ERR(cuse_class))
609 return PTR_ERR(cuse_class);
611 cuse_class->dev_attrs = cuse_class_dev_attrs;
613 rc = misc_register(&cuse_miscdev);
615 class_destroy(cuse_class);
622 static void __exit cuse_exit(void)
624 misc_deregister(&cuse_miscdev);
625 class_destroy(cuse_class);
628 module_init(cuse_init);
629 module_exit(cuse_exit);
631 MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
632 MODULE_DESCRIPTION("Character device in Userspace");
633 MODULE_LICENSE("GPL");