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/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
  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_iter(struct kiocb *kiocb, struct iov_iter *to)
  92 {
  93         struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
  94         loff_t pos = 0;
  95
  96         return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
  97 }
  98
  99 static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
 100 {
 101         struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb);
 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
 111 static 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
 141 static 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
 152 static 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
 165 static 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
 178 static 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
 195 struct 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  */
 215 static 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  */
 268 static 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
 295 static 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  */
 307 static 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);
 396 out:
 397         kfree(arg);
 398         __free_page(page);
 399         return;
 400
 401 err_cdev:
 402         cdev_del(cdev);
 403 err_unlock:
 404         mutex_unlock(&cuse_lock);
 405         put_device(dev);
 406 err_region:
 407         unregister_chrdev_region(devt, 1);
 408 err:
 409         fuse_abort_conn(fc);
 410         goto out;
 411 }
 412
 413 static 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
 461 err_free_page:
 462         __free_page(page);
 463 err_put_req:
 464         fuse_put_request(fc, req);
 465 err:
 466         return rc;
 467 }
 468
 469 static 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  */
 490 static int cuse_channel_open(struct inode *inode, struct file *file)
 491 {
 492         struct fuse_dev *fud;
 493         struct cuse_conn *cc;
 494         int rc;
 495
 496         /* set up cuse_conn */
 497         cc = kzalloc(sizeof(*cc), GFP_KERNEL);
 498         if (!cc)
 499                 return -ENOMEM;
 500
 501         fuse_conn_init(&cc->fc);
 502
 503         fud = fuse_dev_alloc(&cc->fc);
 504         if (!fud) {
 505                 kfree(cc);
 506                 return -ENOMEM;
 507         }
 508
 509         INIT_LIST_HEAD(&cc->list);
 510         cc->fc.release = cuse_fc_release;
 511
 512         cc->fc.initialized = 1;
 513         rc = cuse_send_init(cc);
 514         if (rc) {
 515                 fuse_dev_free(fud);
 516                 return rc;
 517         }
 518         file->private_data = fud;
 519
 520         return 0;
 521 }
 522
 523 /**
 524  * cuse_channel_release - release method for /dev/cuse
 525  * @inode: inode for /dev/cuse
 526  * @file: file struct being closed
 527  *
 528  * Disconnect the channel, deregister CUSE device and initiate
 529  * destruction by putting the default reference.
 530  *
 531  * RETURNS:
 532  * 0 on success, -errno on failure.
 533  */
 534 static int cuse_channel_release(struct inode *inode, struct file *file)
 535 {
 536         struct fuse_dev *fud = file->private_data;
 537         struct cuse_conn *cc = fc_to_cc(fud->fc);
 538         int rc;
 539
 540         /* remove from the conntbl, no more access from this point on */
 541         mutex_lock(&cuse_lock);
 542         list_del_init(&cc->list);
 543         mutex_unlock(&cuse_lock);
 544
 545         /* remove device */
 546         if (cc->dev)
 547                 device_unregister(cc->dev);
 548         if (cc->cdev) {
 549                 unregister_chrdev_region(cc->cdev->dev, 1);
 550                 cdev_del(cc->cdev);
 551         }
 552         /* Base reference is now owned by "fud" */
 553         fuse_conn_put(&cc->fc);
 554
 555         rc = fuse_dev_release(inode, file);     /* puts the base reference */
 556
 557         return rc;
 558 }
 559
 560 static struct file_operations cuse_channel_fops; /* initialized during init */
 561
 562
 563 /**************************************************************************
 564  * Misc stuff and module initializatiion
 565  *
 566  * CUSE exports the same set of attributes to sysfs as fusectl.
 567  */
 568
 569 static ssize_t cuse_class_waiting_show(struct device *dev,
 570                                        struct device_attribute *attr, char *buf)
 571 {
 572         struct cuse_conn *cc = dev_get_drvdata(dev);
 573
 574         return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
 575 }
 576 static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);
 577
 578 static ssize_t cuse_class_abort_store(struct device *dev,
 579                                       struct device_attribute *attr,
 580                                       const char *buf, size_t count)
 581 {
 582         struct cuse_conn *cc = dev_get_drvdata(dev);
 583
 584         fuse_abort_conn(&cc->fc);
 585         return count;
 586 }
 587 static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
 588
 589 static struct attribute *cuse_class_dev_attrs[] = {
 590         &dev_attr_waiting.attr,
 591         &dev_attr_abort.attr,
 592         NULL,
 593 };
 594 ATTRIBUTE_GROUPS(cuse_class_dev);
 595
 596 static struct miscdevice cuse_miscdev = {
 597         .minor          = CUSE_MINOR,
 598         .name           = "cuse",
 599         .fops           = &cuse_channel_fops,
 600 };
 601
 602 MODULE_ALIAS_MISCDEV(CUSE_MINOR);
 603 MODULE_ALIAS("devname:cuse");
 604
 605 static int __init cuse_init(void)
 606 {
 607         int i, rc;
 608
 609         /* init conntbl */
 610         for (i = 0; i < CUSE_CONNTBL_LEN; i++)
 611                 INIT_LIST_HEAD(&cuse_conntbl[i]);
 612
 613         /* inherit and extend fuse_dev_operations */
 614         cuse_channel_fops               = fuse_dev_operations;
 615         cuse_channel_fops.owner         = THIS_MODULE;
 616         cuse_channel_fops.open          = cuse_channel_open;
 617         cuse_channel_fops.release       = cuse_channel_release;
 618
 619         cuse_class = class_create(THIS_MODULE, "cuse");
 620         if (IS_ERR(cuse_class))
 621                 return PTR_ERR(cuse_class);
 622
 623         cuse_class->dev_groups = cuse_class_dev_groups;
 624
 625         rc = misc_register(&cuse_miscdev);
 626         if (rc) {
 627                 class_destroy(cuse_class);
 628                 return rc;
 629         }
 630
 631         return 0;
 632 }
 633
 634 static void __exit cuse_exit(void)
 635 {
 636         misc_deregister(&cuse_miscdev);
 637         class_destroy(cuse_class);
 638 }
 639
 640 module_init(cuse_init);
 641 module_exit(cuse_exit);
 642
 643 MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
 644 MODULE_DESCRIPTION("Character device in Userspace");
 645 MODULE_LICENSE("GPL");