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 <asm/uaccess.h>
  10 #include <asm/semaphore.h>
  11
  12 #include "sysfs.h"
  13
  14 #define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
  15 #define to_sattr(a) container_of(a,struct subsys_attribute,attr)
  16
  17 /*
  18  * Subsystem file operations.
  19  * These operations allow subsystems to have files that can be
  20  * read/written.
  21  */
  22 static ssize_t
  23 subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
  24 {
  25         struct subsystem * s = to_subsys(kobj);
  26         struct subsys_attribute * sattr = to_sattr(attr);
  27         ssize_t ret = -EIO;
  28
  29         if (sattr->show)
  30                 ret = sattr->show(s,page);
  31         return ret;
  32 }
  33
  34 static ssize_t
  35 subsys_attr_store(struct kobject * kobj, struct attribute * attr,
  36                   const char * page, size_t count)
  37 {
  38         struct subsystem * s = to_subsys(kobj);
  39         struct subsys_attribute * sattr = to_sattr(attr);
  40         ssize_t ret = -EIO;
  41
  42         if (sattr->store)
  43                 ret = sattr->store(s,page,count);
  44         return ret;
  45 }
  46
  47 static struct sysfs_ops subsys_sysfs_ops = {
  48         .show   = subsys_attr_show,
  49         .store  = subsys_attr_store,
  50 };
  51
  52
  53 struct sysfs_buffer {
  54         size_t                  count;
  55         loff_t                  pos;
  56         char                    * page;
  57         struct sysfs_ops        * ops;
  58         struct semaphore        sem;
  59         int                     needs_read_fill;
  60 };
  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.
  72  */
  73 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
  74 {
  75         struct attribute * attr = to_attr(dentry);
  76         struct kobject * kobj = to_kobj(dentry->d_parent);
  77         struct sysfs_ops * ops = buffer->ops;
  78         int ret = 0;
  79         ssize_t count;
  80
  81         if (!buffer->page)
  82                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  83         if (!buffer->page)
  84                 return -ENOMEM;
  85
  86         count = ops->show(kobj,attr,buffer->page);
  87         buffer->needs_read_fill = 0;
  88         BUG_ON(count > (ssize_t)PAGE_SIZE);
  89         if (count >= 0)
  90                 buffer->count = count;
  91         else
  92                 ret = count;
  93         return ret;
  94 }
  95
  96
  97 /**
  98  *      flush_read_buffer - push buffer to userspace.
  99  *      @buffer:        data buffer for file.
 100  *      @buf:           user-passed buffer.
 101  *      @count:         number of bytes requested.
 102  *      @ppos:          file position.
 103  *
 104  *      Copy the buffer we filled in fill_read_buffer() to userspace.
 105  *      This is done at the reader's leisure, copying and advancing
 106  *      the amount they specify each time.
 107  *      This may be called continuously until the buffer is empty.
 108  */
 109 static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
 110                              size_t count, loff_t * ppos)
 111 {
 112         int error;
 113
 114         if (*ppos > buffer->count)
 115                 return 0;
 116
 117         if (count > (buffer->count - *ppos))
 118                 count = buffer->count - *ppos;
 119
 120         error = copy_to_user(buf,buffer->page + *ppos,count);
 121         if (!error)
 122                 *ppos += count;
 123         return error ? -EFAULT : count;
 124 }
 125
 126 /**
 127  *      sysfs_read_file - read an attribute.
 128  *      @file:  file pointer.
 129  *      @buf:   buffer to fill.
 130  *      @count: number of bytes to read.
 131  *      @ppos:  starting offset in file.
 132  *
 133  *      Userspace wants to read an attribute file. The attribute descriptor
 134  *      is in the file's ->d_fsdata. The target object is in the directory's
 135  *      ->d_fsdata.
 136  *
 137  *      We call fill_read_buffer() to allocate and fill the buffer from the
 138  *      object's show() method exactly once (if the read is happening from
 139  *      the beginning of the file). That should fill the entire buffer with
 140  *      all the data the object has to offer for that attribute.
 141  *      We then call flush_read_buffer() to copy the buffer to userspace
 142  *      in the increments specified.
 143  */
 144
 145 static ssize_t
 146 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 147 {
 148         struct sysfs_buffer * buffer = file->private_data;
 149         ssize_t retval = 0;
 150
 151         down(&buffer->sem);
 152         if (buffer->needs_read_fill) {
 153                 if ((retval = fill_read_buffer(file->f_dentry,buffer)))
 154                         goto out;
 155         }
 156         pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
 157                  __FUNCTION__,count,*ppos,buffer->page);
 158         retval = flush_read_buffer(buffer,buf,count,ppos);
 159 out:
 160         up(&buffer->sem);
 161         return retval;
 162 }
 163
 164
 165 /**
 166  *      fill_write_buffer - copy buffer from userspace.
 167  *      @buffer:        data buffer for file.
 168  *      @buf:           data from user.
 169  *      @count:         number of bytes in @userbuf.
 170  *
 171  *      Allocate @buffer->page if it hasn't been already, then
 172  *      copy the user-supplied buffer into it.
 173  */
 174
 175 static int
 176 fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
 177 {
 178         int error;
 179
 180         if (!buffer->page)
 181                 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
 182         if (!buffer->page)
 183                 return -ENOMEM;
 184
 185         if (count >= PAGE_SIZE)
 186                 count = PAGE_SIZE;
 187         error = copy_from_user(buffer->page,buf,count);
 188         buffer->needs_read_fill = 1;
 189         return error ? -EFAULT : count;
 190 }
 191
 192
 193 /**
 194  *      flush_write_buffer - push buffer to kobject.
 195  *      @dentry:        dentry to the attribute
 196  *      @buffer:        data buffer for file.
 197  *      @count:         number of bytes
 198  *
 199  *      Get the correct pointers for the kobject and the attribute we're
 200  *      dealing with, then call the store() method for the attribute,
 201  *      passing the buffer that we acquired in fill_write_buffer().
 202  */
 203
 204 static int
 205 flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
 206 {
 207         struct attribute * attr = to_attr(dentry);
 208         struct kobject * kobj = to_kobj(dentry->d_parent);
 209         struct sysfs_ops * ops = buffer->ops;
 210
 211         return ops->store(kobj,attr,buffer->page,count);
 212 }
 213
 214
 215 /**
 216  *      sysfs_write_file - write an attribute.
 217  *      @file:  file pointer
 218  *      @buf:   data to write
 219  *      @count: number of bytes
 220  *      @ppos:  starting offset
 221  *
 222  *      Similar to sysfs_read_file(), though working in the opposite direction.
 223  *      We allocate and fill the data from the user in fill_write_buffer(),
 224  *      then push it to the kobject in flush_write_buffer().
 225  *      There is no easy way for us to know if userspace is only doing a partial
 226  *      write, so we don't support them. We expect the entire buffer to come
 227  *      on the first write.
 228  *      Hint: if you're writing a value, first read the file, modify only the
 229  *      the value you're changing, then write entire buffer back.
 230  */
 231
 232 static ssize_t
 233 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 234 {
 235         struct sysfs_buffer * buffer = file->private_data;
 236         ssize_t len;
 237
 238         down(&buffer->sem);
 239         len = fill_write_buffer(buffer, buf, count);
 240         if (len > 0)
 241                 len = flush_write_buffer(file->f_dentry, buffer, len);
 242         if (len > 0)
 243                 *ppos += len;
 244         up(&buffer->sem);
 245         return len;
 246 }
 247
 248 static int check_perm(struct inode * inode, struct file * file)
 249 {
 250         struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent);
 251         struct attribute * attr = to_attr(file->f_dentry);
 252         struct sysfs_buffer * buffer;
 253         struct sysfs_ops * ops = NULL;
 254         int error = 0;
 255
 256         if (!kobj || !attr)
 257                 goto Einval;
 258
 259         /* Grab the module reference for this attribute if we have one */
 260         if (!try_module_get(attr->owner)) {
 261                 error = -ENODEV;
 262                 goto Done;
 263         }
 264
 265         /* if the kobject has no ktype, then we assume that it is a subsystem
 266          * itself, and use ops for it.
 267          */
 268         if (kobj->kset && kobj->kset->ktype)
 269                 ops = kobj->kset->ktype->sysfs_ops;
 270         else if (kobj->ktype)
 271                 ops = kobj->ktype->sysfs_ops;
 272         else
 273                 ops = &subsys_sysfs_ops;
 274
 275         /* No sysfs operations, either from having no subsystem,
 276          * or the subsystem have no operations.
 277          */
 278         if (!ops)
 279                 goto Eaccess;
 280
 281         /* File needs write support.
 282          * The inode's perms must say it's ok,
 283          * and we must have a store method.
 284          */
 285         if (file->f_mode & FMODE_WRITE) {
 286
 287                 if (!(inode->i_mode & S_IWUGO) || !ops->store)
 288                         goto Eaccess;
 289
 290         }
 291
 292         /* File needs read support.
 293          * The inode's perms must say it's ok, and we there
 294          * must be a show method for it.
 295          */
 296         if (file->f_mode & FMODE_READ) {
 297                 if (!(inode->i_mode & S_IRUGO) || !ops->show)
 298                         goto Eaccess;
 299         }
 300
 301         /* No error? Great, allocate a buffer for the file, and store it
 302          * it in file->private_data for easy access.
 303          */
 304         buffer = kmalloc(sizeof(struct sysfs_buffer),GFP_KERNEL);
 305         if (buffer) {
 306                 memset(buffer,0,sizeof(struct sysfs_buffer));
 307                 init_MUTEX(&buffer->sem);
 308                 buffer->needs_read_fill = 1;
 309                 buffer->ops = ops;
 310                 file->private_data = buffer;
 311         } else
 312                 error = -ENOMEM;
 313         goto Done;
 314
 315  Einval:
 316         error = -EINVAL;
 317         goto Done;
 318  Eaccess:
 319         error = -EACCES;
 320         module_put(attr->owner);
 321  Done:
 322         if (error && kobj)
 323                 kobject_put(kobj);
 324         return error;
 325 }
 326
 327 static int sysfs_open_file(struct inode * inode, struct file * filp)
 328 {
 329         return check_perm(inode,filp);
 330 }
 331
 332 static int sysfs_release(struct inode * inode, struct file * filp)
 333 {
 334         struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
 335         struct attribute * attr = to_attr(filp->f_dentry);
 336         struct module * owner = attr->owner;
 337         struct sysfs_buffer * buffer = filp->private_data;
 338
 339         if (kobj)
 340                 kobject_put(kobj);
 341         /* After this point, attr should not be accessed. */
 342         module_put(owner);
 343
 344         if (buffer) {
 345                 if (buffer->page)
 346                         free_page((unsigned long)buffer->page);
 347                 kfree(buffer);
 348         }
 349         return 0;
 350 }
 351
 352 struct file_operations sysfs_file_operations = {
 353         .read           = sysfs_read_file,
 354         .write          = sysfs_write_file,
 355         .llseek         = generic_file_llseek,
 356         .open           = sysfs_open_file,
 357         .release        = sysfs_release,
 358 };
 359
 360
 361 int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
 362 {
 363         struct sysfs_dirent * parent_sd = dir->d_fsdata;
 364         umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
 365         int error = 0;
 366
 367         down(&dir->d_inode->i_sem);
 368         error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 369         up(&dir->d_inode->i_sem);
 370
 371         return error;
 372 }
 373
 374
 375 /**
 376  *      sysfs_create_file - create an attribute file for an object.
 377  *      @kobj:  object we're creating for.
 378  *      @attr:  atrribute descriptor.
 379  */
 380
 381 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
 382 {
 383         BUG_ON(!kobj || !kobj->dentry || !attr);
 384
 385         return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);
 386
 387 }
 388
 389
 390 /**
 391  * sysfs_update_file - update the modified timestamp on an object attribute.
 392  * @kobj: object we're acting for.
 393  * @attr: attribute descriptor.
 394  */
 395 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 396 {
 397         struct dentry * dir = kobj->dentry;
 398         struct dentry * victim;
 399         int res = -ENOENT;
 400
 401         down(&dir->d_inode->i_sem);
 402         victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 403         if (!IS_ERR(victim)) {
 404                 /* make sure dentry is really there */
 405                 if (victim->d_inode &&
 406                     (victim->d_parent->d_inode == dir->d_inode)) {
 407                         victim->d_inode->i_mtime = CURRENT_TIME;
 408                         fsnotify_modify(victim);
 409
 410                         /**
 411                          * Drop reference from initial sysfs_get_dentry().
 412                          */
 413                         dput(victim);
 414                         res = 0;
 415                 } else
 416                         d_drop(victim);
 417
 418                 /**
 419                  * Drop the reference acquired from sysfs_get_dentry() above.
 420                  */
 421                 dput(victim);
 422         }
 423         up(&dir->d_inode->i_sem);
 424
 425         return res;
 426 }
 427
 428
 429 /**
 430  * sysfs_chmod_file - update the modified mode value on an object attribute.
 431  * @kobj: object we're acting for.
 432  * @attr: attribute descriptor.
 433  * @mode: file permissions.
 434  *
 435  */
 436 int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
 437 {
 438         struct dentry *dir = kobj->dentry;
 439         struct dentry *victim;
 440         struct inode * inode;
 441         struct iattr newattrs;
 442         int res = -ENOENT;
 443
 444         down(&dir->d_inode->i_sem);
 445         victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 446         if (!IS_ERR(victim)) {
 447                 if (victim->d_inode &&
 448                     (victim->d_parent->d_inode == dir->d_inode)) {
 449                         inode = victim->d_inode;
 450                         down(&inode->i_sem);
 451                         newattrs.ia_mode = (mode & S_IALLUGO) |
 452                                                 (inode->i_mode & ~S_IALLUGO);
 453                         newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
 454                         res = notify_change(victim, &newattrs);
 455                         up(&inode->i_sem);
 456                 }
 457                 dput(victim);
 458         }
 459         up(&dir->d_inode->i_sem);
 460
 461         return res;
 462 }
 463 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
 464
 465
 466 /**
 467  *      sysfs_remove_file - remove an object attribute.
 468  *      @kobj:  object we're acting for.
 469  *      @attr:  attribute descriptor.
 470  *
 471  *      Hash the attribute name and kill the victim.
 472  */
 473
 474 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
 475 {
 476         sysfs_hash_and_remove(kobj->dentry,attr->name);
 477 }
 478
 479
 480 EXPORT_SYMBOL_GPL(sysfs_create_file);
 481 EXPORT_SYMBOL_GPL(sysfs_remove_file);
 482 EXPORT_SYMBOL_GPL(sysfs_update_file);
 483