fs/sysfs/file.c

   1 /*
   2  * file.c - operations for regular (text) files.
   3  */
   4
   5 #include <linux/module.h>
   6 #include <linux/fsnotify.h>
   7 #include <linux/kobject.h>
   8 #include <linux/namei.h>
   9 #include <linux/poll.h>
  10 #include <linux/list.h>
  11 #include <asm/uaccess.h>
  12 #include <asm/semaphore.h>
  13
  14 #include "sysfs.h"
  15
  16 #define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
  17 #define to_sattr(a) container_of(a,struct subsys_attribute,attr)
  18
  19 /*
  20  * Subsystem file operations.
  21  * These operations allow subsystems to have files that can be
  22  * read/written.
  23  */
  24 static ssize_t
  25 subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
  26 {
  27         struct subsystem * s = to_subsys(kobj);
  28         struct subsys_attribute * sattr = to_sattr(attr);
  29         ssize_t ret = -EIO;
  30
  31         if (sattr->show)
  32                 ret = sattr->show(s,page);
  33         return ret;
  34 }
  35
  36 static ssize_t
  37 subsys_attr_store(struct kobject * kobj, struct attribute * attr,
  38                   const char * page, size_t count)
  39 {
  40         struct subsystem * s = to_subsys(kobj);
  41         struct subsys_attribute * sattr = to_sattr(attr);
  42         ssize_t ret = -EIO;
  43
  44         if (sattr->store)
  45                 ret = sattr->store(s,page,count);
  46         return ret;
  47 }
  48
  49 static struct sysfs_ops subsys_sysfs_ops = {
  50         .show   = subsys_attr_show,
  51         .store  = subsys_attr_store,
  52 };
  53
  54 /**
  55  *      add_to_collection - add buffer to a collection
  56  *      @buffer:        buffer to be added
  57  *      @node:          inode of set to add to
  58  */
  59
  60 static inline void
  61 add_to_collection(struct sysfs_buffer *buffer, struct inode *node)
  62 {
  63         struct sysfs_buffer_collection *set = node->i_private;
  64
  65         mutex_lock(&node->i_mutex);
  66         list_add(&buffer->associates, &set->associates);
  67         mutex_unlock(&node->i_mutex);
  68 }
  69
  70 static inline void
  71 remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
  72 {
  73         mutex_lock(&node->i_mutex);
  74         list_del(&buffer->associates);
  75         mutex_unlock(&node->i_mutex);
  76 }
  77
  78 /**
  79  *      fill_read_buffer - allocate and fill buffer from object.
  80  *      @dentry:        dentry pointer.
  81  *      @buffer:        data buffer for file.
  82  *
  83  *      Allocate @buffer->page, if it hasn't been already, then call the
  84  *      kobject's show() method to fill the buffer with this attribute's
  85  *      data.
  86  *      This is called only once, on the file's first read unless an error
  87  *      is returned.
  88  */
  89 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
  90 {
  91         struct sysfs_dirent * sd = dentry->d_fsdata;
  92         struct attribute * attr = to_attr(dentry);
  93         struct kobject * kobj = to_kobj(dentry->d_parent);
  94         struct sysfs_ops * ops = buffer->ops;
  95         int ret = 0;
  96         ssize_t count;
  97
  98         if (!buffer->page)
  99                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
 100         if (!buffer->page)
 101                 return -ENOMEM;
 102
 103         buffer->event = atomic_read(&sd->s_event);
 104         count = ops->show(kobj,attr,buffer->page);
 105         BUG_ON(count > (ssize_t)PAGE_SIZE);
 106         if (count >= 0) {
 107                 buffer->needs_read_fill = 0;
 108                 buffer->count = count;
 109         } else {
 110                 ret = count;
 111         }
 112         return ret;
 113 }
 114
 115
 116 /**
 117  *      flush_read_buffer - push buffer to userspace.
 118  *      @buffer:        data buffer for file.
 119  *      @buf:           user-passed buffer.
 120  *      @count:         number of bytes requested.
 121  *      @ppos:          file position.
 122  *
 123  *      Copy the buffer we filled in fill_read_buffer() to userspace.
 124  *      This is done at the reader's leisure, copying and advancing
 125  *      the amount they specify each time.
 126  *      This may be called continuously until the buffer is empty.
 127  */
 128 static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
 129                              size_t count, loff_t * ppos)
 130 {
 131         int error;
 132
 133         if (*ppos > buffer->count)
 134                 return 0;
 135
 136         if (count > (buffer->count - *ppos))
 137                 count = buffer->count - *ppos;
 138
 139         error = copy_to_user(buf,buffer->page + *ppos,count);
 140         if (!error)
 141                 *ppos += count;
 142         return error ? -EFAULT : count;
 143 }
 144
 145 /**
 146  *      sysfs_read_file - read an attribute.
 147  *      @file:  file pointer.
 148  *      @buf:   buffer to fill.
 149  *      @count: number of bytes to read.
 150  *      @ppos:  starting offset in file.
 151  *
 152  *      Userspace wants to read an attribute file. The attribute descriptor
 153  *      is in the file's ->d_fsdata. The target object is in the directory's
 154  *      ->d_fsdata.
 155  *
 156  *      We call fill_read_buffer() to allocate and fill the buffer from the
 157  *      object's show() method exactly once (if the read is happening from
 158  *      the beginning of the file). That should fill the entire buffer with
 159  *      all the data the object has to offer for that attribute.
 160  *      We then call flush_read_buffer() to copy the buffer to userspace
 161  *      in the increments specified.
 162  */
 163
 164 static ssize_t
 165 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 166 {
 167         struct sysfs_buffer * buffer = file->private_data;
 168         ssize_t retval = 0;
 169
 170         down(&buffer->sem);
 171         if (buffer->orphaned) {
 172                 retval = -ENODEV;
 173                 goto out;
 174         }
 175         if (buffer->needs_read_fill) {
 176                 if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
 177                         goto out;
 178         }
 179         pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
 180                  __FUNCTION__, count, *ppos, buffer->page);
 181         retval = flush_read_buffer(buffer,buf,count,ppos);
 182 out:
 183         up(&buffer->sem);
 184         return retval;
 185 }
 186
 187 /**
 188  *      fill_write_buffer - copy buffer from userspace.
 189  *      @buffer:        data buffer for file.
 190  *      @buf:           data from user.
 191  *      @count:         number of bytes in @userbuf.
 192  *
 193  *      Allocate @buffer->page if it hasn't been already, then
 194  *      copy the user-supplied buffer into it.
 195  */
 196
 197 static int
 198 fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
 199 {
 200         int error;
 201
 202         if (!buffer->page)
 203                 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
 204         if (!buffer->page)
 205                 return -ENOMEM;
 206
 207         if (count >= PAGE_SIZE)
 208                 count = PAGE_SIZE - 1;
 209         error = copy_from_user(buffer->page,buf,count);
 210         buffer->needs_read_fill = 1;
 211         /* if buf is assumed to contain a string, terminate it by \0,
 212            so e.g. sscanf() can scan the string easily */
 213         buffer->page[count] = 0;
 214         return error ? -EFAULT : count;
 215 }
 216
 217
 218 /**
 219  *      flush_write_buffer - push buffer to kobject.
 220  *      @dentry:        dentry to the attribute
 221  *      @buffer:        data buffer for file.
 222  *      @count:         number of bytes
 223  *
 224  *      Get the correct pointers for the kobject and the attribute we're
 225  *      dealing with, then call the store() method for the attribute,
 226  *      passing the buffer that we acquired in fill_write_buffer().
 227  */
 228
 229 static int
 230 flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
 231 {
 232         struct attribute * attr = to_attr(dentry);
 233         struct kobject * kobj = to_kobj(dentry->d_parent);
 234         struct sysfs_ops * ops = buffer->ops;
 235
 236         return ops->store(kobj,attr,buffer->page,count);
 237 }
 238
 239
 240 /**
 241  *      sysfs_write_file - write an attribute.
 242  *      @file:  file pointer
 243  *      @buf:   data to write
 244  *      @count: number of bytes
 245  *      @ppos:  starting offset
 246  *
 247  *      Similar to sysfs_read_file(), though working in the opposite direction.
 248  *      We allocate and fill the data from the user in fill_write_buffer(),
 249  *      then push it to the kobject in flush_write_buffer().
 250  *      There is no easy way for us to know if userspace is only doing a partial
 251  *      write, so we don't support them. We expect the entire buffer to come
 252  *      on the first write.
 253  *      Hint: if you're writing a value, first read the file, modify only the
 254  *      the value you're changing, then write entire buffer back.
 255  */
 256
 257 static ssize_t
 258 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 259 {
 260         struct sysfs_buffer * buffer = file->private_data;
 261         ssize_t len;
 262
 263         down(&buffer->sem);
 264         if (buffer->orphaned) {
 265                 len = -ENODEV;
 266                 goto out;
 267         }
 268         len = fill_write_buffer(buffer, buf, count);
 269         if (len > 0)
 270                 len = flush_write_buffer(file->f_path.dentry, buffer, len);
 271         if (len > 0)
 272                 *ppos += len;
 273 out:
 274         up(&buffer->sem);
 275         return len;
 276 }
 277
 278 static int sysfs_open_file(struct inode *inode, struct file *file)
 279 {
 280         struct kobject *kobj = sysfs_get_kobject(file->f_path.dentry->d_parent);
 281         struct attribute * attr = to_attr(file->f_path.dentry);
 282         struct sysfs_buffer_collection *set;
 283         struct sysfs_buffer * buffer;
 284         struct sysfs_ops * ops = NULL;
 285         int error = 0;
 286
 287         if (!kobj || !attr)
 288                 goto Einval;
 289
 290         /* Grab the module reference for this attribute if we have one */
 291         if (!try_module_get(attr->owner)) {
 292                 error = -ENODEV;
 293                 goto Done;
 294         }
 295
 296         /* if the kobject has no ktype, then we assume that it is a subsystem
 297          * itself, and use ops for it.
 298          */
 299         if (kobj->kset && kobj->kset->ktype)
 300                 ops = kobj->kset->ktype->sysfs_ops;
 301         else if (kobj->ktype)
 302                 ops = kobj->ktype->sysfs_ops;
 303         else
 304                 ops = &subsys_sysfs_ops;
 305
 306         /* No sysfs operations, either from having no subsystem,
 307          * or the subsystem have no operations.
 308          */
 309         if (!ops)
 310                 goto Eaccess;
 311
 312         /* make sure we have a collection to add our buffers to */
 313         mutex_lock(&inode->i_mutex);
 314         if (!(set = inode->i_private)) {
 315                 if (!(set = inode->i_private = kmalloc(sizeof(struct sysfs_buffer_collection), GFP_KERNEL))) {
 316                         error = -ENOMEM;
 317                         goto Done;
 318                 } else {
 319                         INIT_LIST_HEAD(&set->associates);
 320                 }
 321         }
 322         mutex_unlock(&inode->i_mutex);
 323
 324         /* File needs write support.
 325          * The inode's perms must say it's ok,
 326          * and we must have a store method.
 327          */
 328         if (file->f_mode & FMODE_WRITE) {
 329
 330                 if (!(inode->i_mode & S_IWUGO) || !ops->store)
 331                         goto Eaccess;
 332
 333         }
 334
 335         /* File needs read support.
 336          * The inode's perms must say it's ok, and we there
 337          * must be a show method for it.
 338          */
 339         if (file->f_mode & FMODE_READ) {
 340                 if (!(inode->i_mode & S_IRUGO) || !ops->show)
 341                         goto Eaccess;
 342         }
 343
 344         /* No error? Great, allocate a buffer for the file, and store it
 345          * it in file->private_data for easy access.
 346          */
 347         buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
 348         if (buffer) {
 349                 INIT_LIST_HEAD(&buffer->associates);
 350                 init_MUTEX(&buffer->sem);
 351                 buffer->needs_read_fill = 1;
 352                 buffer->ops = ops;
 353                 add_to_collection(buffer, inode);
 354                 file->private_data = buffer;
 355         } else
 356                 error = -ENOMEM;
 357         goto Done;
 358
 359  Einval:
 360         error = -EINVAL;
 361         goto Done;
 362  Eaccess:
 363         error = -EACCES;
 364         module_put(attr->owner);
 365  Done:
 366         if (error)
 367                 kobject_put(kobj);
 368         return error;
 369 }
 370
 371 static int sysfs_release(struct inode * inode, struct file * filp)
 372 {
 373         struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
 374         struct attribute * attr = to_attr(filp->f_path.dentry);
 375         struct module * owner = attr->owner;
 376         struct sysfs_buffer * buffer = filp->private_data;
 377
 378         if (buffer)
 379                 remove_from_collection(buffer, inode);
 380         kobject_put(kobj);
 381         /* After this point, attr should not be accessed. */
 382         module_put(owner);
 383
 384         if (buffer) {
 385                 if (buffer->page)
 386                         free_page((unsigned long)buffer->page);
 387                 kfree(buffer);
 388         }
 389         return 0;
 390 }
 391
 392 /* Sysfs attribute files are pollable.  The idea is that you read
 393  * the content and then you use 'poll' or 'select' to wait for
 394  * the content to change.  When the content changes (assuming the
 395  * manager for the kobject supports notification), poll will
 396  * return POLLERR|POLLPRI, and select will return the fd whether
 397  * it is waiting for read, write, or exceptions.
 398  * Once poll/select indicates that the value has changed, you
 399  * need to close and re-open the file, as simply seeking and reading
 400  * again will not get new data, or reset the state of 'poll'.
 401  * Reminder: this only works for attributes which actively support
 402  * it, and it is not possible to test an attribute from userspace
 403  * to see if it supports poll (Nether 'poll' or 'select' return
 404  * an appropriate error code).  When in doubt, set a suitable timeout value.
 405  */
 406 static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
 407 {
 408         struct sysfs_buffer * buffer = filp->private_data;
 409         struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
 410         struct sysfs_dirent * sd = filp->f_path.dentry->d_fsdata;
 411         int res = 0;
 412
 413         poll_wait(filp, &kobj->poll, wait);
 414
 415         if (buffer->event != atomic_read(&sd->s_event)) {
 416                 res = POLLERR|POLLPRI;
 417                 buffer->needs_read_fill = 1;
 418         }
 419
 420         return res;
 421 }
 422
 423
 424 static struct dentry *step_down(struct dentry *dir, const char * name)
 425 {
 426         struct dentry * de;
 427
 428         if (dir == NULL || dir->d_inode == NULL)
 429                 return NULL;
 430
 431         mutex_lock(&dir->d_inode->i_mutex);
 432         de = lookup_one_len(name, dir, strlen(name));
 433         mutex_unlock(&dir->d_inode->i_mutex);
 434         dput(dir);
 435         if (IS_ERR(de))
 436                 return NULL;
 437         if (de->d_inode == NULL) {
 438                 dput(de);
 439                 return NULL;
 440         }
 441         return de;
 442 }
 443
 444 void sysfs_notify(struct kobject * k, char *dir, char *attr)
 445 {
 446         struct dentry *de = k->dentry;
 447         if (de)
 448                 dget(de);
 449         if (de && dir)
 450                 de = step_down(de, dir);
 451         if (de && attr)
 452                 de = step_down(de, attr);
 453         if (de) {
 454                 struct sysfs_dirent * sd = de->d_fsdata;
 455                 if (sd)
 456                         atomic_inc(&sd->s_event);
 457                 wake_up_interruptible(&k->poll);
 458                 dput(de);
 459         }
 460 }
 461 EXPORT_SYMBOL_GPL(sysfs_notify);
 462
 463 const struct file_operations sysfs_file_operations = {
 464         .read           = sysfs_read_file,
 465         .write          = sysfs_write_file,
 466         .llseek         = generic_file_llseek,
 467         .open           = sysfs_open_file,
 468         .release        = sysfs_release,
 469         .poll           = sysfs_poll,
 470 };
 471
 472
 473 int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
 474 {
 475         struct sysfs_dirent * parent_sd = dir->d_fsdata;
 476         umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
 477         int error = -EEXIST;
 478
 479         mutex_lock(&dir->d_inode->i_mutex);
 480         if (!sysfs_dirent_exist(parent_sd, attr->name))
 481                 error = sysfs_make_dirent(parent_sd, NULL, (void *)attr,
 482                                           mode, type);
 483         mutex_unlock(&dir->d_inode->i_mutex);
 484
 485         return error;
 486 }
 487
 488
 489 /**
 490  *      sysfs_create_file - create an attribute file for an object.
 491  *      @kobj:  object we're creating for.
 492  *      @attr:  atrribute descriptor.
 493  */
 494
 495 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
 496 {
 497         BUG_ON(!kobj || !kobj->dentry || !attr);
 498
 499         return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);
 500
 501 }
 502
 503
 504 /**
 505  * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 506  * @kobj: object we're acting for.
 507  * @attr: attribute descriptor.
 508  * @group: group name.
 509  */
 510 int sysfs_add_file_to_group(struct kobject *kobj,
 511                 const struct attribute *attr, const char *group)
 512 {
 513         struct dentry *dir;
 514         int error;
 515
 516         dir = lookup_one_len(group, kobj->dentry, strlen(group));
 517         if (IS_ERR(dir))
 518                 error = PTR_ERR(dir);
 519         else {
 520                 error = sysfs_add_file(dir, attr, SYSFS_KOBJ_ATTR);
 521                 dput(dir);
 522         }
 523         return error;
 524 }
 525 EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
 526
 527
 528 /**
 529  * sysfs_update_file - update the modified timestamp on an object attribute.
 530  * @kobj: object we're acting for.
 531  * @attr: attribute descriptor.
 532  */
 533 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 534 {
 535         struct dentry * dir = kobj->dentry;
 536         struct dentry * victim;
 537         int res = -ENOENT;
 538
 539         mutex_lock(&dir->d_inode->i_mutex);
 540         victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 541         if (!IS_ERR(victim)) {
 542                 /* make sure dentry is really there */
 543                 if (victim->d_inode &&
 544                     (victim->d_parent->d_inode == dir->d_inode)) {
 545                         victim->d_inode->i_mtime = CURRENT_TIME;
 546                         fsnotify_modify(victim);
 547                         res = 0;
 548                 } else
 549                         d_drop(victim);
 550
 551                 /**
 552                  * Drop the reference acquired from lookup_one_len() above.
 553                  */
 554                 dput(victim);
 555         }
 556         mutex_unlock(&dir->d_inode->i_mutex);
 557
 558         return res;
 559 }
 560
 561
 562 /**
 563  * sysfs_chmod_file - update the modified mode value on an object attribute.
 564  * @kobj: object we're acting for.
 565  * @attr: attribute descriptor.
 566  * @mode: file permissions.
 567  *
 568  */
 569 int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
 570 {
 571         struct dentry *dir = kobj->dentry;
 572         struct dentry *victim;
 573         struct inode * inode;
 574         struct iattr newattrs;
 575         int res = -ENOENT;
 576
 577         mutex_lock(&dir->d_inode->i_mutex);
 578         victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 579         if (!IS_ERR(victim)) {
 580                 if (victim->d_inode &&
 581                     (victim->d_parent->d_inode == dir->d_inode)) {
 582                         inode = victim->d_inode;
 583                         mutex_lock(&inode->i_mutex);
 584                         newattrs.ia_mode = (mode & S_IALLUGO) |
 585                                                 (inode->i_mode & ~S_IALLUGO);
 586                         newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
 587                         res = notify_change(victim, &newattrs);
 588                         mutex_unlock(&inode->i_mutex);
 589                 }
 590                 dput(victim);
 591         }
 592         mutex_unlock(&dir->d_inode->i_mutex);
 593
 594         return res;
 595 }
 596 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
 597
 598
 599 /**
 600  *      sysfs_remove_file - remove an object attribute.
 601  *      @kobj:  object we're acting for.
 602  *      @attr:  attribute descriptor.
 603  *
 604  *      Hash the attribute name and kill the victim.
 605  */
 606
 607 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
 608 {
 609         sysfs_hash_and_remove(kobj->dentry, attr->name);
 610 }
 611
 612
 613 /**
 614  * sysfs_remove_file_from_group - remove an attribute file from a group.
 615  * @kobj: object we're acting for.
 616  * @attr: attribute descriptor.
 617  * @group: group name.
 618  */
 619 void sysfs_remove_file_from_group(struct kobject *kobj,
 620                 const struct attribute *attr, const char *group)
 621 {
 622         struct dentry *dir;
 623
 624         dir = lookup_one_len(group, kobj->dentry, strlen(group));
 625         if (!IS_ERR(dir)) {
 626                 sysfs_hash_and_remove(dir, attr->name);
 627                 dput(dir);
 628         }
 629 }
 630 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
 631
 632 struct sysfs_schedule_callback_struct {
 633         struct kobject          *kobj;
 634         void                    (*func)(void *);
 635         void                    *data;
 636         struct work_struct      work;
 637 };
 638
 639 static void sysfs_schedule_callback_work(struct work_struct *work)
 640 {
 641         struct sysfs_schedule_callback_struct *ss = container_of(work,
 642                         struct sysfs_schedule_callback_struct, work);
 643
 644         (ss->func)(ss->data);
 645         kobject_put(ss->kobj);
 646         kfree(ss);
 647 }
 648
 649 /**
 650  * sysfs_schedule_callback - helper to schedule a callback for a kobject
 651  * @kobj: object we're acting for.
 652  * @func: callback function to invoke later.
 653  * @data: argument to pass to @func.
 654  *
 655  * sysfs attribute methods must not unregister themselves or their parent
 656  * kobject (which would amount to the same thing).  Attempts to do so will
 657  * deadlock, since unregistration is mutually exclusive with driver
 658  * callbacks.
 659  *
 660  * Instead methods can call this routine, which will attempt to allocate
 661  * and schedule a workqueue request to call back @func with @data as its
 662  * argument in the workqueue's process context.  @kobj will be pinned
 663  * until @func returns.
 664  *
 665  * Returns 0 if the request was submitted, -ENOMEM if storage could not
 666  * be allocated.
 667  */
 668 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
 669                 void *data)
 670 {
 671         struct sysfs_schedule_callback_struct *ss;
 672
 673         ss = kmalloc(sizeof(*ss), GFP_KERNEL);
 674         if (!ss)
 675                 return -ENOMEM;
 676         kobject_get(kobj);
 677         ss->kobj = kobj;
 678         ss->func = func;
 679         ss->data = data;
 680         INIT_WORK(&ss->work, sysfs_schedule_callback_work);
 681         schedule_work(&ss->work);
 682         return 0;
 683 }
 684 EXPORT_SYMBOL_GPL(sysfs_schedule_callback);
 685
 686
 687 EXPORT_SYMBOL_GPL(sysfs_create_file);
 688 EXPORT_SYMBOL_GPL(sysfs_remove_file);
 689 EXPORT_SYMBOL_GPL(sysfs_update_file);