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