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