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