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
  56struct 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
  66static DEFINE_MUTEX(cuse_lock);         /* protects registration */
  67static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
  68static struct class *cuse_class;
  69
  70static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
  71{
  72        return container_of(fc, struct cuse_conn, fc);
  73}
  74
  75static 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
  91static 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
 101static 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
 115static 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
 145static 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
 156static 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
 169static 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
 182static 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
 199struct 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 */
 219static 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 */
 272static 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
 299static 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 */
 311static 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);
 400out:
 401        kfree(arg);
 402        __free_page(page);
 403        return;
 404
 405err_cdev:
 406        cdev_del(cdev);
 407err_unlock:
 408        mutex_unlock(&cuse_lock);
 409        put_device(dev);
 410err_region:
 411        unregister_chrdev_region(devt, 1);
 412err:
 413        fuse_conn_kill(fc);
 414        goto out;
 415}
 416
 417static 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
 465err_free_page:
 466        __free_page(page);
 467err_put_req:
 468        fuse_put_request(fc, req);
 469err:
 470        return rc;
 471}
 472
 473static void cuse_fc_release(struct fuse_conn *fc)
 474{
 475        struct cuse_conn *cc = fc_to_cc(fc);
 476        kfree_rcu(cc, fc.rcu);
 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 */
 494static 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 */
 532static 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
 555static 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
 564static 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}
 571static DEVICE_ATTR(waiting, S_IFREG | 0400, cuse_class_waiting_show, NULL);
 572
 573static ssize_t cuse_class_abort_store(struct device *dev,
 574                                      struct device_attribute *attr,
 575                                      const char *buf, size_t count)
 576{
 577        struct cuse_conn *cc = dev_get_drvdata(dev);
 578
 579        fuse_abort_conn(&cc->fc);
 580        return count;
 581}
 582static DEVICE_ATTR(abort, S_IFREG | 0200, NULL, cuse_class_abort_store);
 583
 584static struct attribute *cuse_class_dev_attrs[] = {
 585        &dev_attr_waiting.attr,
 586        &dev_attr_abort.attr,
 587        NULL,
 588};
 589ATTRIBUTE_GROUPS(cuse_class_dev);
 590
 591static struct miscdevice cuse_miscdev = {
 592        .minor          = CUSE_MINOR,
 593        .name           = "cuse",
 594        .fops           = &cuse_channel_fops,
 595};
 596
 597MODULE_ALIAS_MISCDEV(CUSE_MINOR);
 598MODULE_ALIAS("devname:cuse");
 599
 600static int __init cuse_init(void)
 601{
 602        int i, rc;
 603
 604        /* init conntbl */
 605        for (i = 0; i < CUSE_CONNTBL_LEN; i++)
 606                INIT_LIST_HEAD(&cuse_conntbl[i]);
 607
 608        /* inherit and extend fuse_dev_operations */
 609        cuse_channel_fops               = fuse_dev_operations;
 610        cuse_channel_fops.owner         = THIS_MODULE;
 611        cuse_channel_fops.open          = cuse_channel_open;
 612        cuse_channel_fops.release       = cuse_channel_release;
 613
 614        cuse_class = class_create(THIS_MODULE, "cuse");
 615        if (IS_ERR(cuse_class))
 616                return PTR_ERR(cuse_class);
 617
 618        cuse_class->dev_groups = cuse_class_dev_groups;
 619
 620        rc = misc_register(&cuse_miscdev);
 621        if (rc) {
 622                class_destroy(cuse_class);
 623                return rc;
 624        }
 625
 626        return 0;
 627}
 628
 629static void __exit cuse_exit(void)
 630{
 631        misc_deregister(&cuse_miscdev);
 632        class_destroy(cuse_class);
 633}
 634
 635module_init(cuse_init);
 636module_exit(cuse_exit);
 637
 638MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
 639MODULE_DESCRIPTION("Character device in Userspace");
 640MODULE_LICENSE("GPL");
 641