fs/sysfs/file.c

   1 /*
   2  * file.c - operations for regular (text) files.
   3  */
   4
   5 #include <linux/module.h>
   6 #include <linux/dnotify.h>
   7 #include <linux/kobject.h>
   8 #include <asm/uaccess.h>
   9 #include <asm/semaphore.h>
  10
  11 #include "sysfs.h"
  12
  13 #define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
  14 #define to_sattr(a) container_of(a,struct subsys_attribute,attr)
  15
  16 /**
  17  * Subsystem file operations.
  18  * These operations allow subsystems to have files that can be
  19  * read/written.
  20  */
  21 static ssize_t
  22 subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
  23 {
  24         struct subsystem * s = to_subsys(kobj);
  25         struct subsys_attribute * sattr = to_sattr(attr);
  26         ssize_t ret = 0;
  27
  28         if (sattr->show)
  29                 ret = sattr->show(s,page);
  30         return ret;
  31 }
  32
  33 static ssize_t
  34 subsys_attr_store(struct kobject * kobj, struct attribute * attr,
  35                   const char * page, size_t count)
  36 {
  37         struct subsystem * s = to_subsys(kobj);
  38         struct subsys_attribute * sattr = to_sattr(attr);
  39         ssize_t ret = 0;
  40
  41         if (sattr->store)
  42                 ret = sattr->store(s,page,count);
  43         return ret;
  44 }
  45
  46 static struct sysfs_ops subsys_sysfs_ops = {
  47         .show   = subsys_attr_show,
  48         .store  = subsys_attr_store,
  49 };
  50
  51
  52 struct sysfs_buffer {
  53         size_t                  count;
  54         loff_t                  pos;
  55         char                    * page;
  56         struct sysfs_ops        * ops;
  57         struct semaphore        sem;
  58         int                     needs_read_fill;
  59 };
  60
  61
  62 /**
  63  *      fill_read_buffer - allocate and fill buffer from object.
  64  *      @dentry:        dentry pointer.
  65  *      @buffer:        data buffer for file.
  66  *
  67  *      Allocate @buffer->page, if it hasn't been already, then call the
  68  *      kobject's show() method to fill the buffer with this attribute's
  69  *      data.
  70  *      This is called only once, on the file's first read.
  71  */
  72 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
  73 {
  74         struct attribute * attr = to_attr(dentry);
  75         struct kobject * kobj = to_kobj(dentry->d_parent);
  76         struct sysfs_ops * ops = buffer->ops;
  77         int ret = 0;
  78         ssize_t count;
  79
  80         if (!buffer->page)
  81                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  82         if (!buffer->page)
  83                 return -ENOMEM;
  84
  85         count = ops->show(kobj,attr,buffer->page);
  86         buffer->needs_read_fill = 0;
  87         BUG_ON(count > (ssize_t)PAGE_SIZE);
  88         if (count >= 0)
  89                 buffer->count = count;
  90         else
  91                 ret = count;
  92         return ret;
  93 }
  94
  95
  96 /**
  97  *      flush_read_buffer - push buffer to userspace.
  98  *      @buffer:        data buffer for file.
  99  *      @userbuf:       user-passed buffer.
 100  *      @count:         number of bytes requested.
 101  *      @ppos:          file position.
 102  *
 103  *      Copy the buffer we filled in fill_read_buffer() to userspace.
 104  *      This is done at the reader's leisure, copying and advancing
 105  *      the amount they specify each time.
 106  *      This may be called continuously until the buffer is empty.
 107  */
 108 static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
 109                              size_t count, loff_t * ppos)
 110 {
 111         int error;
 112
 113         if (*ppos > buffer->count)
 114                 return 0;
 115
 116         if (count > (buffer->count - *ppos))
 117                 count = buffer->count - *ppos;
 118
 119         error = copy_to_user(buf,buffer->page + *ppos,count);
 120         if (!error)
 121                 *ppos += count;
 122         return error ? -EFAULT : count;
 123 }
 124
 125 /**
 126  *      sysfs_read_file - read an attribute.
 127  *      @file:  file pointer.
 128  *      @buf:   buffer to fill.
 129  *      @count: number of bytes to read.
 130  *      @ppos:  starting offset in file.
 131  *
 132  *      Userspace wants to read an attribute file. The attribute descriptor
 133  *      is in the file's ->d_fsdata. The target object is in the directory's
 134  *      ->d_fsdata.
 135  *
 136  *      We call fill_read_buffer() to allocate and fill the buffer from the
 137  *      object's show() method exactly once (if the read is happening from
 138  *      the beginning of the file). That should fill the entire buffer with
 139  *      all the data the object has to offer for that attribute.
 140  *      We then call flush_read_buffer() to copy the buffer to userspace
 141  *      in the increments specified.
 142  */
 143
 144 static ssize_t
 145 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 146 {
 147         struct sysfs_buffer * buffer = file->private_data;
 148         ssize_t retval = 0;
 149
 150         down(&buffer->sem);
 151         if (buffer->needs_read_fill) {
 152                 if ((retval = fill_read_buffer(file->f_dentry,buffer)))
 153                         goto out;
 154         }
 155         pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
 156                  __FUNCTION__,count,*ppos,buffer->page);
 157         retval = flush_read_buffer(buffer,buf,count,ppos);
 158 out:
 159         up(&buffer->sem);
 160         return retval;
 161 }
 162
 163
 164 /**
 165  *      fill_write_buffer - copy buffer from userspace.
 166  *      @buffer:        data buffer for file.
 167  *      @userbuf:       data from user.
 168  *      @count:         number of bytes in @userbuf.
 169  *
 170  *      Allocate @buffer->page if it hasn't been already, then
 171  *      copy the user-supplied buffer into it.
 172  */
 173
 174 static int
 175 fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
 176 {
 177         int error;
 178
 179         if (!buffer->page)
 180                 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
 181         if (!buffer->page)
 182                 return -ENOMEM;
 183
 184         if (count >= PAGE_SIZE)
 185                 count = PAGE_SIZE - 1;
 186         error = copy_from_user(buffer->page,buf,count);
 187         buffer->needs_read_fill = 1;
 188         return error ? -EFAULT : count;
 189 }
 190
 191
 192 /**
 193  *      flush_write_buffer - push buffer to kobject.
 194  *      @file:          file pointer.
 195  *      @buffer:        data buffer for file.
 196  *
 197  *      Get the correct pointers for the kobject and the attribute we're
 198  *      dealing with, then call the store() method for the attribute,
 199  *      passing the buffer that we acquired in fill_write_buffer().
 200  */
 201
 202 static int
 203 flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
 204 {
 205         struct attribute * attr = to_attr(dentry);
 206         struct kobject * kobj = to_kobj(dentry->d_parent);
 207         struct sysfs_ops * ops = buffer->ops;
 208
 209         return ops->store(kobj,attr,buffer->page,count);
 210 }
 211
 212
 213 /**
 214  *      sysfs_write_file - write an attribute.
 215  *      @file:  file pointer
 216  *      @buf:   data to write
 217  *      @count: number of bytes
 218  *      @ppos:  starting offset
 219  *
 220  *      Similar to sysfs_read_file(), though working in the opposite direction.
 221  *      We allocate and fill the data from the user in fill_write_buffer(),
 222  *      then push it to the kobject in flush_write_buffer().
 223  *      There is no easy way for us to know if userspace is only doing a partial
 224  *      write, so we don't support them. We expect the entire buffer to come
 225  *      on the first write.
 226  *      Hint: if you're writing a value, first read the file, modify only the
 227  *      the value you're changing, then write entire buffer back.
 228  */
 229
 230 static ssize_t
 231 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 232 {
 233         struct sysfs_buffer * buffer = file->private_data;
 234         ssize_t len;
 235
 236         down(&buffer->sem);
 237         len = fill_write_buffer(buffer, buf, count);
 238         if (len > 0)
 239                 len = flush_write_buffer(file->f_dentry, buffer, len);
 240         if (len > 0)
 241                 *ppos += len;
 242         up(&buffer->sem);
 243         return len;
 244 }
 245
 246 static int check_perm(struct inode * inode, struct file * file)
 247 {
 248         struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent);
 249         struct attribute * attr = to_attr(file->f_dentry);
 250         struct sysfs_buffer * buffer;
 251         struct sysfs_ops * ops = NULL;
 252         int error = 0;
 253
 254         if (!kobj || !attr)
 255                 goto Einval;
 256
 257         /* Grab the module reference for this attribute if we have one */
 258         if (!try_module_get(attr->owner)) {
 259                 error = -ENODEV;
 260                 goto Done;
 261         }
 262
 263         /* if the kobject has no ktype, then we assume that it is a subsystem
 264          * itself, and use ops for it.
 265          */
 266         if (kobj->kset && kobj->kset->ktype)
 267                 ops = kobj->kset->ktype->sysfs_ops;
 268         else if (kobj->ktype)
 269                 ops = kobj->ktype->sysfs_ops;
 270         else
 271                 ops = &subsys_sysfs_ops;
 272
 273         /* No sysfs operations, either from having no subsystem,
 274          * or the subsystem have no operations.
 275          */
 276         if (!ops)
 277                 goto Eaccess;
 278
 279         /* File needs write support.
 280          * The inode's perms must say it's ok,
 281          * and we must have a store method.
 282          */
 283         if (file->f_mode & FMODE_WRITE) {
 284
 285                 if (!(inode->i_mode & S_IWUGO) || !ops->store)
 286                         goto Eaccess;
 287
 288         }
 289
 290         /* File needs read support.
 291          * The inode's perms must say it's ok, and we there
 292          * must be a show method for it.
 293          */
 294         if (file->f_mode & FMODE_READ) {
 295                 if (!(inode->i_mode & S_IRUGO) || !ops->show)
 296                         goto Eaccess;
 297         }
 298
 299         /* No error? Great, allocate a buffer for the file, and store it
 300          * it in file->private_data for easy access.
 301          */
 302         buffer = kmalloc(sizeof(struct sysfs_buffer),GFP_KERNEL);
 303         if (buffer) {
 304                 memset(buffer,0,sizeof(struct sysfs_buffer));
 305                 init_MUTEX(&buffer->sem);
 306                 buffer->needs_read_fill = 1;
 307                 buffer->ops = ops;
 308                 file->private_data = buffer;
 309         } else
 310                 error = -ENOMEM;
 311         goto Done;
 312
 313  Einval:
 314         error = -EINVAL;
 315         goto Done;
 316  Eaccess:
 317         error = -EACCES;
 318         module_put(attr->owner);
 319  Done:
 320         if (error && kobj)
 321                 kobject_put(kobj);
 322         return error;
 323 }
 324
 325 static int sysfs_open_file(struct inode * inode, struct file * filp)
 326 {
 327         return check_perm(inode,filp);
 328 }
 329
 330 static int sysfs_release(struct inode * inode, struct file * filp)
 331 {
 332         struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
 333         struct attribute * attr = to_attr(filp->f_dentry);
 334         struct module * owner = attr->owner;
 335         struct sysfs_buffer * buffer = filp->private_data;
 336
 337         if (kobj)
 338                 kobject_put(kobj);
 339         /* After this point, attr should not be accessed. */
 340         module_put(owner);
 341
 342         if (buffer) {
 343                 if (buffer->page)
 344                         free_page((unsigned long)buffer->page);
 345                 kfree(buffer);
 346         }
 347         return 0;
 348 }
 349
 350 struct file_operations sysfs_file_operations = {
 351         .read           = sysfs_read_file,
 352         .write          = sysfs_write_file,
 353         .llseek         = generic_file_llseek,
 354         .open           = sysfs_open_file,
 355         .release        = sysfs_release,
 356 };
 357
 358
 359 int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
 360 {
 361         struct sysfs_dirent * parent_sd = dir->d_fsdata;
 362         umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
 363         int error = 0;
 364
 365         down(&dir->d_inode->i_sem);
 366         error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 367         up(&dir->d_inode->i_sem);
 368
 369         return error;
 370 }
 371
 372
 373 /**
 374  *      sysfs_create_file - create an attribute file for an object.
 375  *      @kobj:  object we're creating for.
 376  *      @attr:  atrribute descriptor.
 377  */
 378
 379 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
 380 {
 381         BUG_ON(!kobj || !kobj->dentry || !attr);
 382
 383         return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);
 384
 385 }
 386
 387
 388 /**
 389  * sysfs_update_file - update the modified timestamp on an object attribute.
 390  * @kobj: object we're acting for.
 391  * @attr: attribute descriptor.
 392  *
 393  * Also call dnotify for the dentry, which lots of userspace programs
 394  * use.
 395  */
 396 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 397 {
 398         struct dentry * dir = kobj->dentry;
 399         struct dentry * victim;
 400         int res = -ENOENT;
 401
 402         down(&dir->d_inode->i_sem);
 403         victim = sysfs_get_dentry(dir, attr->name);
 404         if (!IS_ERR(victim)) {
 405                 /* make sure dentry is really there */
 406                 if (victim->d_inode &&
 407                     (victim->d_parent->d_inode == dir->d_inode)) {
 408                         victim->d_inode->i_mtime = CURRENT_TIME;
 409                         dnotify_parent(victim, DN_MODIFY);
 410
 411                         /**
 412                          * Drop reference from initial sysfs_get_dentry().
 413                          */
 414                         dput(victim);
 415                         res = 0;
 416                 } else
 417                         d_drop(victim);
 418
 419                 /**
 420                  * Drop the reference acquired from sysfs_get_dentry() above.
 421                  */
 422                 dput(victim);
 423         }
 424         up(&dir->d_inode->i_sem);
 425
 426         return res;
 427 }
 428
 429
 430 /**
 431  *      sysfs_remove_file - remove an object attribute.
 432  *      @kobj:  object we're acting for.
 433  *      @attr:  attribute descriptor.
 434  *
 435  *      Hash the attribute name and kill the victim.
 436  */
 437
 438 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
 439 {
 440         sysfs_hash_and_remove(kobj->dentry,attr->name);
 441 }
 442
 443
 444 EXPORT_SYMBOL_GPL(sysfs_create_file);
 445 EXPORT_SYMBOL_GPL(sysfs_remove_file);
 446 EXPORT_SYMBOL_GPL(sysfs_update_file);
 447