fs/fuse/cuse.c

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