fs/sysfs/file.c

   1 /*
   2  * fs/sysfs/file.c - sysfs regular (text) file implementation
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   7  *
   8  * This file is released under the GPLv2.
   9  *
  10  * Please see Documentation/filesystems/sysfs.txt for more information.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/kobject.h>
  15 #include <linux/kallsyms.h>
  16 #include <linux/slab.h>
  17 #include <linux/fsnotify.h>
  18 #include <linux/namei.h>
  19 #include <linux/poll.h>
  20 #include <linux/list.h>
  21 #include <linux/mutex.h>
  22 #include <linux/limits.h>
  23 #include <asm/uaccess.h>
  24
  25 #include "sysfs.h"
  26
  27 /*
  28  * There's one sysfs_buffer for each open file and one
  29  * sysfs_open_dirent for each sysfs_dirent with one or more open
  30  * files.
  31  *
  32  * filp->private_data points to sysfs_buffer and
  33  * sysfs_dirent->s_attr.open points to sysfs_open_dirent.  s_attr.open
  34  * is protected by sysfs_open_dirent_lock.
  35  */
  36 static DEFINE_SPINLOCK(sysfs_open_dirent_lock);
  37
  38 struct sysfs_open_dirent {
  39         atomic_t                refcnt;
  40         atomic_t                event;
  41         wait_queue_head_t       poll;
  42         struct list_head        buffers; /* goes through sysfs_buffer.list */
  43 };
  44
  45 struct sysfs_buffer {
  46         size_t                  count;
  47         loff_t                  pos;
  48         char                    * page;
  49         const struct sysfs_ops  * ops;
  50         struct mutex            mutex;
  51         int                     needs_read_fill;
  52         int                     event;
  53         struct list_head        list;
  54 };
  55
  56 /**
  57  *      fill_read_buffer - allocate and fill buffer from object.
  58  *      @dentry:        dentry pointer.
  59  *      @buffer:        data buffer for file.
  60  *
  61  *      Allocate @buffer->page, if it hasn't been already, then call the
  62  *      kobject's show() method to fill the buffer with this attribute's
  63  *      data.
  64  *      This is called only once, on the file's first read unless an error
  65  *      is returned.
  66  */
  67 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
  68 {
  69         struct sysfs_dirent *attr_sd = dentry->d_fsdata;
  70         struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
  71         const struct sysfs_ops * ops = buffer->ops;
  72         int ret = 0;
  73         ssize_t count;
  74
  75         if (!buffer->page)
  76                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  77         if (!buffer->page)
  78                 return -ENOMEM;
  79
  80         /* need attr_sd for attr and ops, its parent for kobj */
  81         if (!sysfs_get_active(attr_sd))
  82                 return -ENODEV;
  83
  84         buffer->event = atomic_read(&attr_sd->s_attr.open->event);
  85         count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);
  86
  87         sysfs_put_active(attr_sd);
  88
  89         /*
  90          * The code works fine with PAGE_SIZE return but it's likely to
  91          * indicate truncated result or overflow in normal use cases.
  92          */
  93         if (count >= (ssize_t)PAGE_SIZE) {
  94                 print_symbol("fill_read_buffer: %s returned bad count\n",
  95                         (unsigned long)ops->show);
  96                 /* Try to struggle along */
  97                 count = PAGE_SIZE - 1;
  98         }
  99         if (count >= 0) {
 100                 buffer->needs_read_fill = 0;
 101                 buffer->count = count;
 102         } else {
 103                 ret = count;
 104         }
 105         return ret;
 106 }
 107
 108 /**
 109  *      sysfs_read_file - read an attribute.
 110  *      @file:  file pointer.
 111  *      @buf:   buffer to fill.
 112  *      @count: number of bytes to read.
 113  *      @ppos:  starting offset in file.
 114  *
 115  *      Userspace wants to read an attribute file. The attribute descriptor
 116  *      is in the file's ->d_fsdata. The target object is in the directory's
 117  *      ->d_fsdata.
 118  *
 119  *      We call fill_read_buffer() to allocate and fill the buffer from the
 120  *      object's show() method exactly once (if the read is happening from
 121  *      the beginning of the file). That should fill the entire buffer with
 122  *      all the data the object has to offer for that attribute.
 123  *      We then call flush_read_buffer() to copy the buffer to userspace
 124  *      in the increments specified.
 125  */
 126
 127 static ssize_t
 128 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 129 {
 130         struct sysfs_buffer * buffer = file->private_data;
 131         ssize_t retval = 0;
 132
 133         mutex_lock(&buffer->mutex);
 134         if (buffer->needs_read_fill || *ppos == 0) {
 135                 retval = fill_read_buffer(file->f_path.dentry,buffer);
 136                 if (retval)
 137                         goto out;
 138         }
 139         pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
 140                  __func__, count, *ppos, buffer->page);
 141         retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
 142                                          buffer->count);
 143 out:
 144         mutex_unlock(&buffer->mutex);
 145         return retval;
 146 }
 147
 148 /**
 149  *      fill_write_buffer - copy buffer from userspace.
 150  *      @buffer:        data buffer for file.
 151  *      @buf:           data from user.
 152  *      @count:         number of bytes in @userbuf.
 153  *
 154  *      Allocate @buffer->page if it hasn't been already, then
 155  *      copy the user-supplied buffer into it.
 156  */
 157
 158 static int
 159 fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
 160 {
 161         int error;
 162
 163         if (!buffer->page)
 164                 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
 165         if (!buffer->page)
 166                 return -ENOMEM;
 167
 168         if (count >= PAGE_SIZE)
 169                 count = PAGE_SIZE - 1;
 170         error = copy_from_user(buffer->page,buf,count);
 171         buffer->needs_read_fill = 1;
 172         /* if buf is assumed to contain a string, terminate it by \0,
 173            so e.g. sscanf() can scan the string easily */
 174         buffer->page[count] = 0;
 175         return error ? -EFAULT : count;
 176 }
 177
 178
 179 /**
 180  *      flush_write_buffer - push buffer to kobject.
 181  *      @dentry:        dentry to the attribute
 182  *      @buffer:        data buffer for file.
 183  *      @count:         number of bytes
 184  *
 185  *      Get the correct pointers for the kobject and the attribute we're
 186  *      dealing with, then call the store() method for the attribute,
 187  *      passing the buffer that we acquired in fill_write_buffer().
 188  */
 189
 190 static int
 191 flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
 192 {
 193         struct sysfs_dirent *attr_sd = dentry->d_fsdata;
 194         struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
 195         const struct sysfs_ops * ops = buffer->ops;
 196         int rc;
 197
 198         /* need attr_sd for attr and ops, its parent for kobj */
 199         if (!sysfs_get_active(attr_sd))
 200                 return -ENODEV;
 201
 202         rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);
 203
 204         sysfs_put_active(attr_sd);
 205
 206         return rc;
 207 }
 208
 209
 210 /**
 211  *      sysfs_write_file - write an attribute.
 212  *      @file:  file pointer
 213  *      @buf:   data to write
 214  *      @count: number of bytes
 215  *      @ppos:  starting offset
 216  *
 217  *      Similar to sysfs_read_file(), though working in the opposite direction.
 218  *      We allocate and fill the data from the user in fill_write_buffer(),
 219  *      then push it to the kobject in flush_write_buffer().
 220  *      There is no easy way for us to know if userspace is only doing a partial
 221  *      write, so we don't support them. We expect the entire buffer to come
 222  *      on the first write.
 223  *      Hint: if you're writing a value, first read the file, modify only the
 224  *      the value you're changing, then write entire buffer back.
 225  */
 226
 227 static ssize_t
 228 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 229 {
 230         struct sysfs_buffer * buffer = file->private_data;
 231         ssize_t len;
 232
 233         mutex_lock(&buffer->mutex);
 234         len = fill_write_buffer(buffer, buf, count);
 235         if (len > 0)
 236                 len = flush_write_buffer(file->f_path.dentry, buffer, len);
 237         if (len > 0)
 238                 *ppos += len;
 239         mutex_unlock(&buffer->mutex);
 240         return len;
 241 }
 242
 243 /**
 244  *      sysfs_get_open_dirent - get or create sysfs_open_dirent
 245  *      @sd: target sysfs_dirent
 246  *      @buffer: sysfs_buffer for this instance of open
 247  *
 248  *      If @sd->s_attr.open exists, increment its reference count;
 249  *      otherwise, create one.  @buffer is chained to the buffers
 250  *      list.
 251  *
 252  *      LOCKING:
 253  *      Kernel thread context (may sleep).
 254  *
 255  *      RETURNS:
 256  *      0 on success, -errno on failure.
 257  */
 258 static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
 259                                  struct sysfs_buffer *buffer)
 260 {
 261         struct sysfs_open_dirent *od, *new_od = NULL;
 262
 263  retry:
 264         spin_lock_irq(&sysfs_open_dirent_lock);
 265
 266         if (!sd->s_attr.open && new_od) {
 267                 sd->s_attr.open = new_od;
 268                 new_od = NULL;
 269         }
 270
 271         od = sd->s_attr.open;
 272         if (od) {
 273                 atomic_inc(&od->refcnt);
 274                 list_add_tail(&buffer->list, &od->buffers);
 275         }
 276
 277         spin_unlock_irq(&sysfs_open_dirent_lock);
 278
 279         if (od) {
 280                 kfree(new_od);
 281                 return 0;
 282         }
 283
 284         /* not there, initialize a new one and retry */
 285         new_od = kmalloc(sizeof(*new_od), GFP_KERNEL);
 286         if (!new_od)
 287                 return -ENOMEM;
 288
 289         atomic_set(&new_od->refcnt, 0);
 290         atomic_set(&new_od->event, 1);
 291         init_waitqueue_head(&new_od->poll);
 292         INIT_LIST_HEAD(&new_od->buffers);
 293         goto retry;
 294 }
 295
 296 /**
 297  *      sysfs_put_open_dirent - put sysfs_open_dirent
 298  *      @sd: target sysfs_dirent
 299  *      @buffer: associated sysfs_buffer
 300  *
 301  *      Put @sd->s_attr.open and unlink @buffer from the buffers list.
 302  *      If reference count reaches zero, disassociate and free it.
 303  *
 304  *      LOCKING:
 305  *      None.
 306  */
 307 static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
 308                                   struct sysfs_buffer *buffer)
 309 {
 310         struct sysfs_open_dirent *od = sd->s_attr.open;
 311         unsigned long flags;
 312
 313         spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 314
 315         list_del(&buffer->list);
 316         if (atomic_dec_and_test(&od->refcnt))
 317                 sd->s_attr.open = NULL;
 318         else
 319                 od = NULL;
 320
 321         spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
 322
 323         kfree(od);
 324 }
 325
 326 static int sysfs_open_file(struct inode *inode, struct file *file)
 327 {
 328         struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
 329         struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
 330         struct sysfs_buffer *buffer;
 331         const struct sysfs_ops *ops;
 332         int error = -EACCES;
 333
 334         /* need attr_sd for attr and ops, its parent for kobj */
 335         if (!sysfs_get_active(attr_sd))
 336                 return -ENODEV;
 337
 338         /* every kobject with an attribute needs a ktype assigned */
 339         if (kobj->ktype && kobj->ktype->sysfs_ops)
 340                 ops = kobj->ktype->sysfs_ops;
 341         else {
 342                 WARN(1, KERN_ERR "missing sysfs attribute operations for "
 343                        "kobject: %s\n", kobject_name(kobj));
 344                 goto err_out;
 345         }
 346
 347         /* File needs write support.
 348          * The inode's perms must say it's ok,
 349          * and we must have a store method.
 350          */
 351         if (file->f_mode & FMODE_WRITE) {
 352                 if (!(inode->i_mode & S_IWUGO) || !ops->store)
 353                         goto err_out;
 354         }
 355
 356         /* File needs read support.
 357          * The inode's perms must say it's ok, and we there
 358          * must be a show method for it.
 359          */
 360         if (file->f_mode & FMODE_READ) {
 361                 if (!(inode->i_mode & S_IRUGO) || !ops->show)
 362                         goto err_out;
 363         }
 364
 365         /* No error? Great, allocate a buffer for the file, and store it
 366          * it in file->private_data for easy access.
 367          */
 368         error = -ENOMEM;
 369         buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
 370         if (!buffer)
 371                 goto err_out;
 372
 373         mutex_init(&buffer->mutex);
 374         buffer->needs_read_fill = 1;
 375         buffer->ops = ops;
 376         file->private_data = buffer;
 377
 378         /* make sure we have open dirent struct */
 379         error = sysfs_get_open_dirent(attr_sd, buffer);
 380         if (error)
 381                 goto err_free;
 382
 383         /* open succeeded, put active references */
 384         sysfs_put_active(attr_sd);
 385         return 0;
 386
 387  err_free:
 388         kfree(buffer);
 389  err_out:
 390         sysfs_put_active(attr_sd);
 391         return error;
 392 }
 393
 394 static int sysfs_release(struct inode *inode, struct file *filp)
 395 {
 396         struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata;
 397         struct sysfs_buffer *buffer = filp->private_data;
 398
 399         sysfs_put_open_dirent(sd, buffer);
 400
 401         if (buffer->page)
 402                 free_page((unsigned long)buffer->page);
 403         kfree(buffer);
 404
 405         return 0;
 406 }
 407
 408 /* Sysfs attribute files are pollable.  The idea is that you read
 409  * the content and then you use 'poll' or 'select' to wait for
 410  * the content to change.  When the content changes (assuming the
 411  * manager for the kobject supports notification), poll will
 412  * return POLLERR|POLLPRI, and select will return the fd whether
 413  * it is waiting for read, write, or exceptions.
 414  * Once poll/select indicates that the value has changed, you
 415  * need to close and re-open the file, or seek to 0 and read again.
 416  * Reminder: this only works for attributes which actively support
 417  * it, and it is not possible to test an attribute from userspace
 418  * to see if it supports poll (Neither 'poll' nor 'select' return
 419  * an appropriate error code).  When in doubt, set a suitable timeout value.
 420  */
 421 static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
 422 {
 423         struct sysfs_buffer * buffer = filp->private_data;
 424         struct sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata;
 425         struct sysfs_open_dirent *od = attr_sd->s_attr.open;
 426
 427         /* need parent for the kobj, grab both */
 428         if (!sysfs_get_active(attr_sd))
 429                 goto trigger;
 430
 431         poll_wait(filp, &od->poll, wait);
 432
 433         sysfs_put_active(attr_sd);
 434
 435         if (buffer->event != atomic_read(&od->event))
 436                 goto trigger;
 437
 438         return DEFAULT_POLLMASK;
 439
 440  trigger:
 441         buffer->needs_read_fill = 1;
 442         return DEFAULT_POLLMASK|POLLERR|POLLPRI;
 443 }
 444
 445 void sysfs_notify_dirent(struct sysfs_dirent *sd)
 446 {
 447         struct sysfs_open_dirent *od;
 448         unsigned long flags;
 449
 450         spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 451
 452         od = sd->s_attr.open;
 453         if (od) {
 454                 atomic_inc(&od->event);
 455                 wake_up_interruptible(&od->poll);
 456         }
 457
 458         spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
 459 }
 460 EXPORT_SYMBOL_GPL(sysfs_notify_dirent);
 461
 462 void sysfs_notify(struct kobject *k, const char *dir, const char *attr)
 463 {
 464         struct sysfs_dirent *sd = k->sd;
 465
 466         mutex_lock(&sysfs_mutex);
 467
 468         if (sd && dir)
 469                 /* Only directories are tagged, so no need to pass
 470                  * a tag explicitly.
 471                  */
 472                 sd = sysfs_find_dirent(sd, NULL, dir);
 473         if (sd && attr)
 474                 sd = sysfs_find_dirent(sd, NULL, attr);
 475         if (sd)
 476                 sysfs_notify_dirent(sd);
 477
 478         mutex_unlock(&sysfs_mutex);
 479 }
 480 EXPORT_SYMBOL_GPL(sysfs_notify);
 481
 482 const struct file_operations sysfs_file_operations = {
 483         .read           = sysfs_read_file,
 484         .write          = sysfs_write_file,
 485         .llseek         = generic_file_llseek,
 486         .open           = sysfs_open_file,
 487         .release        = sysfs_release,
 488         .poll           = sysfs_poll,
 489 };
 490
 491 int sysfs_add_file_mode(struct sysfs_dirent *dir_sd,
 492                         const struct attribute *attr, int type, mode_t amode)
 493 {
 494         umode_t mode = (amode & S_IALLUGO) | S_IFREG;
 495         struct sysfs_addrm_cxt acxt;
 496         struct sysfs_dirent *sd;
 497         int rc;
 498
 499         sd = sysfs_new_dirent(attr->name, mode, type);
 500         if (!sd)
 501                 return -ENOMEM;
 502         sd->s_attr.attr = (void *)attr;
 503         sysfs_dirent_init_lockdep(sd);
 504
 505         sysfs_addrm_start(&acxt, dir_sd);
 506         rc = sysfs_add_one(&acxt, sd);
 507         sysfs_addrm_finish(&acxt);
 508
 509         if (rc)
 510                 sysfs_put(sd);
 511
 512         return rc;
 513 }
 514
 515
 516 int sysfs_add_file(struct sysfs_dirent *dir_sd, const struct attribute *attr,
 517                    int type)
 518 {
 519         return sysfs_add_file_mode(dir_sd, attr, type, attr->mode);
 520 }
 521
 522
 523 /**
 524  *      sysfs_create_file - create an attribute file for an object.
 525  *      @kobj:  object we're creating for.
 526  *      @attr:  attribute descriptor.
 527  */
 528
 529 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
 530 {
 531         BUG_ON(!kobj || !kobj->sd || !attr);
 532
 533         return sysfs_add_file(kobj->sd, attr, SYSFS_KOBJ_ATTR);
 534
 535 }
 536
 537 int sysfs_create_files(struct kobject *kobj, const struct attribute **ptr)
 538 {
 539         int err = 0;
 540         int i;
 541
 542         for (i = 0; ptr[i] && !err; i++)
 543                 err = sysfs_create_file(kobj, ptr[i]);
 544         if (err)
 545                 while (--i >= 0)
 546                         sysfs_remove_file(kobj, ptr[i]);
 547         return err;
 548 }
 549
 550 /**
 551  * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 552  * @kobj: object we're acting for.
 553  * @attr: attribute descriptor.
 554  * @group: group name.
 555  */
 556 int sysfs_add_file_to_group(struct kobject *kobj,
 557                 const struct attribute *attr, const char *group)
 558 {
 559         struct sysfs_dirent *dir_sd;
 560         int error;
 561
 562         if (group)
 563                 dir_sd = sysfs_get_dirent(kobj->sd, NULL, group);
 564         else
 565                 dir_sd = sysfs_get(kobj->sd);
 566
 567         if (!dir_sd)
 568                 return -ENOENT;
 569
 570         error = sysfs_add_file(dir_sd, attr, SYSFS_KOBJ_ATTR);
 571         sysfs_put(dir_sd);
 572
 573         return error;
 574 }
 575 EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
 576
 577 /**
 578  * sysfs_chmod_file - update the modified mode value on an object attribute.
 579  * @kobj: object we're acting for.
 580  * @attr: attribute descriptor.
 581  * @mode: file permissions.
 582  *
 583  */
 584 int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
 585                      mode_t mode)
 586 {
 587         struct sysfs_dirent *sd;
 588         struct iattr newattrs;
 589         int rc;
 590
 591         mutex_lock(&sysfs_mutex);
 592
 593         rc = -ENOENT;
 594         sd = sysfs_find_dirent(kobj->sd, NULL, attr->name);
 595         if (!sd)
 596                 goto out;
 597
 598         newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
 599         newattrs.ia_valid = ATTR_MODE;
 600         rc = sysfs_sd_setattr(sd, &newattrs);
 601
 602  out:
 603         mutex_unlock(&sysfs_mutex);
 604         return rc;
 605 }
 606 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
 607
 608
 609 /**
 610  *      sysfs_remove_file - remove an object attribute.
 611  *      @kobj:  object we're acting for.
 612  *      @attr:  attribute descriptor.
 613  *
 614  *      Hash the attribute name and kill the victim.
 615  */
 616
 617 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
 618 {
 619         sysfs_hash_and_remove(kobj->sd, NULL, attr->name);
 620 }
 621
 622 void sysfs_remove_files(struct kobject * kobj, const struct attribute **ptr)
 623 {
 624         int i;
 625         for (i = 0; ptr[i]; i++)
 626                 sysfs_remove_file(kobj, ptr[i]);
 627 }
 628
 629 /**
 630  * sysfs_remove_file_from_group - remove an attribute file from a group.
 631  * @kobj: object we're acting for.
 632  * @attr: attribute descriptor.
 633  * @group: group name.
 634  */
 635 void sysfs_remove_file_from_group(struct kobject *kobj,
 636                 const struct attribute *attr, const char *group)
 637 {
 638         struct sysfs_dirent *dir_sd;
 639
 640         if (group)
 641                 dir_sd = sysfs_get_dirent(kobj->sd, NULL, group);
 642         else
 643                 dir_sd = sysfs_get(kobj->sd);
 644         if (dir_sd) {
 645                 sysfs_hash_and_remove(dir_sd, NULL, attr->name);
 646                 sysfs_put(dir_sd);
 647         }
 648 }
 649 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
 650
 651 struct sysfs_schedule_callback_struct {
 652         struct list_head        workq_list;
 653         struct kobject          *kobj;
 654         void                    (*func)(void *);
 655         void                    *data;
 656         struct module           *owner;
 657         struct work_struct      work;
 658 };
 659
 660 static struct workqueue_struct *sysfs_workqueue;
 661 static DEFINE_MUTEX(sysfs_workq_mutex);
 662 static LIST_HEAD(sysfs_workq);
 663 static void sysfs_schedule_callback_work(struct work_struct *work)
 664 {
 665         struct sysfs_schedule_callback_struct *ss = container_of(work,
 666                         struct sysfs_schedule_callback_struct, work);
 667
 668         (ss->func)(ss->data);
 669         kobject_put(ss->kobj);
 670         module_put(ss->owner);
 671         mutex_lock(&sysfs_workq_mutex);
 672         list_del(&ss->workq_list);
 673         mutex_unlock(&sysfs_workq_mutex);
 674         kfree(ss);
 675 }
 676
 677 /**
 678  * sysfs_schedule_callback - helper to schedule a callback for a kobject
 679  * @kobj: object we're acting for.
 680  * @func: callback function to invoke later.
 681  * @data: argument to pass to @func.
 682  * @owner: module owning the callback code
 683  *
 684  * sysfs attribute methods must not unregister themselves or their parent
 685  * kobject (which would amount to the same thing).  Attempts to do so will
 686  * deadlock, since unregistration is mutually exclusive with driver
 687  * callbacks.
 688  *
 689  * Instead methods can call this routine, which will attempt to allocate
 690  * and schedule a workqueue request to call back @func with @data as its
 691  * argument in the workqueue's process context.  @kobj will be pinned
 692  * until @func returns.
 693  *
 694  * Returns 0 if the request was submitted, -ENOMEM if storage could not
 695  * be allocated, -ENODEV if a reference to @owner isn't available,
 696  * -EAGAIN if a callback has already been scheduled for @kobj.
 697  */
 698 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
 699                 void *data, struct module *owner)
 700 {
 701         struct sysfs_schedule_callback_struct *ss, *tmp;
 702
 703         if (!try_module_get(owner))
 704                 return -ENODEV;
 705
 706         mutex_lock(&sysfs_workq_mutex);
 707         list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
 708                 if (ss->kobj == kobj) {
 709                         module_put(owner);
 710                         mutex_unlock(&sysfs_workq_mutex);
 711                         return -EAGAIN;
 712                 }
 713         mutex_unlock(&sysfs_workq_mutex);
 714
 715         if (sysfs_workqueue == NULL) {
 716                 sysfs_workqueue = create_singlethread_workqueue("sysfsd");
 717                 if (sysfs_workqueue == NULL) {
 718                         module_put(owner);
 719                         return -ENOMEM;
 720                 }
 721         }
 722
 723         ss = kmalloc(sizeof(*ss), GFP_KERNEL);
 724         if (!ss) {
 725                 module_put(owner);
 726                 return -ENOMEM;
 727         }
 728         kobject_get(kobj);
 729         ss->kobj = kobj;
 730         ss->func = func;
 731         ss->data = data;
 732         ss->owner = owner;
 733         INIT_WORK(&ss->work, sysfs_schedule_callback_work);
 734         INIT_LIST_HEAD(&ss->workq_list);
 735         mutex_lock(&sysfs_workq_mutex);
 736         list_add_tail(&ss->workq_list, &sysfs_workq);
 737         mutex_unlock(&sysfs_workq_mutex);
 738         queue_work(sysfs_workqueue, &ss->work);
 739         return 0;
 740 }
 741 EXPORT_SYMBOL_GPL(sysfs_schedule_callback);
 742
 743
 744 EXPORT_SYMBOL_GPL(sysfs_create_file);
 745 EXPORT_SYMBOL_GPL(sysfs_remove_file);
 746 EXPORT_SYMBOL_GPL(sysfs_remove_files);
 747 EXPORT_SYMBOL_GPL(sysfs_create_files);