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TOMOYO Linux Cross Reference
Linux/fs/fuse/cuse.c

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

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