fs/configfs/file.c

   1 /* -*- mode: c; c-basic-offset: 8; -*-
   2  * vim: noexpandtab sw=8 ts=8 sts=0:
   3  *
   4  * file.c - operations for regular (text) files.
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public
  17  * License along with this program; if not, write to the
  18  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19  * Boston, MA 021110-1307, USA.
  20  *
  21  * Based on sysfs:
  22  *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
  23  *
  24  * configfs Copyright (C) 2005 Oracle.  All rights reserved.
  25  */
  26
  27 #include <linux/fs.h>
  28 #include <linux/module.h>
  29 #include <linux/dnotify.h>
  30 #include <linux/slab.h>
  31 #include <asm/uaccess.h>
  32 #include <asm/semaphore.h>
  33
  34 #include <linux/configfs.h>
  35 #include "configfs_internal.h"
  36
  37
  38 struct configfs_buffer {
  39         size_t                  count;
  40         loff_t                  pos;
  41         char                    * page;
  42         struct configfs_item_operations * ops;
  43         struct semaphore        sem;
  44         int                     needs_read_fill;
  45 };
  46
  47
  48 /**
  49  *      fill_read_buffer - allocate and fill buffer from item.
  50  *      @dentry:        dentry pointer.
  51  *      @buffer:        data buffer for file.
  52  *
  53  *      Allocate @buffer->page, if it hasn't been already, then call the
  54  *      config_item's show() method to fill the buffer with this attribute's
  55  *      data.
  56  *      This is called only once, on the file's first read.
  57  */
  58 static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
  59 {
  60         struct configfs_attribute * attr = to_attr(dentry);
  61         struct config_item * item = to_item(dentry->d_parent);
  62         struct configfs_item_operations * ops = buffer->ops;
  63         int ret = 0;
  64         ssize_t count;
  65
  66         if (!buffer->page)
  67                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  68         if (!buffer->page)
  69                 return -ENOMEM;
  70
  71         count = ops->show_attribute(item,attr,buffer->page);
  72         buffer->needs_read_fill = 0;
  73         BUG_ON(count > (ssize_t)PAGE_SIZE);
  74         if (count >= 0)
  75                 buffer->count = count;
  76         else
  77                 ret = count;
  78         return ret;
  79 }
  80
  81
  82 /**
  83  *      flush_read_buffer - push buffer to userspace.
  84  *      @buffer:        data buffer for file.
  85  *      @userbuf:       user-passed buffer.
  86  *      @count:         number of bytes requested.
  87  *      @ppos:          file position.
  88  *
  89  *      Copy the buffer we filled in fill_read_buffer() to userspace.
  90  *      This is done at the reader's leisure, copying and advancing
  91  *      the amount they specify each time.
  92  *      This may be called continuously until the buffer is empty.
  93  */
  94 static int flush_read_buffer(struct configfs_buffer * buffer, char __user * buf,
  95                              size_t count, loff_t * ppos)
  96 {
  97         int error;
  98
  99         if (*ppos > buffer->count)
 100                 return 0;
 101
 102         if (count > (buffer->count - *ppos))
 103                 count = buffer->count - *ppos;
 104
 105         error = copy_to_user(buf,buffer->page + *ppos,count);
 106         if (!error)
 107                 *ppos += count;
 108         return error ? -EFAULT : count;
 109 }
 110
 111 /**
 112  *      configfs_read_file - read an attribute.
 113  *      @file:  file pointer.
 114  *      @buf:   buffer to fill.
 115  *      @count: number of bytes to read.
 116  *      @ppos:  starting offset in file.
 117  *
 118  *      Userspace wants to read an attribute file. The attribute descriptor
 119  *      is in the file's ->d_fsdata. The target item is in the directory's
 120  *      ->d_fsdata.
 121  *
 122  *      We call fill_read_buffer() to allocate and fill the buffer from the
 123  *      item's show() method exactly once (if the read is happening from
 124  *      the beginning of the file). That should fill the entire buffer with
 125  *      all the data the item has to offer for that attribute.
 126  *      We then call flush_read_buffer() to copy the buffer to userspace
 127  *      in the increments specified.
 128  */
 129
 130 static ssize_t
 131 configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 132 {
 133         struct configfs_buffer * buffer = file->private_data;
 134         ssize_t retval = 0;
 135
 136         down(&buffer->sem);
 137         if (buffer->needs_read_fill) {
 138                 if ((retval = fill_read_buffer(file->f_dentry,buffer)))
 139                         goto out;
 140         }
 141         pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
 142                  __FUNCTION__,count,*ppos,buffer->page);
 143         retval = flush_read_buffer(buffer,buf,count,ppos);
 144 out:
 145         up(&buffer->sem);
 146         return retval;
 147 }
 148
 149
 150 /**
 151  *      fill_write_buffer - copy buffer from userspace.
 152  *      @buffer:        data buffer for file.
 153  *      @userbuf:       data from user.
 154  *      @count:         number of bytes in @userbuf.
 155  *
 156  *      Allocate @buffer->page if it hasn't been already, then
 157  *      copy the user-supplied buffer into it.
 158  */
 159
 160 static int
 161 fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
 162 {
 163         int error;
 164
 165         if (!buffer->page)
 166                 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
 167         if (!buffer->page)
 168                 return -ENOMEM;
 169
 170         if (count > PAGE_SIZE)
 171                 count = PAGE_SIZE;
 172         error = copy_from_user(buffer->page,buf,count);
 173         buffer->needs_read_fill = 1;
 174         return error ? -EFAULT : count;
 175 }
 176
 177
 178 /**
 179  *      flush_write_buffer - push buffer to config_item.
 180  *      @file:          file pointer.
 181  *      @buffer:        data buffer for file.
 182  *
 183  *      Get the correct pointers for the config_item 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 configfs_buffer * buffer, size_t count)
 190 {
 191         struct configfs_attribute * attr = to_attr(dentry);
 192         struct config_item * item = to_item(dentry->d_parent);
 193         struct configfs_item_operations * ops = buffer->ops;
 194
 195         return ops->store_attribute(item,attr,buffer->page,count);
 196 }
 197
 198
 199 /**
 200  *      configfs_write_file - write an attribute.
 201  *      @file:  file pointer
 202  *      @buf:   data to write
 203  *      @count: number of bytes
 204  *      @ppos:  starting offset
 205  *
 206  *      Similar to configfs_read_file(), though working in the opposite direction.
 207  *      We allocate and fill the data from the user in fill_write_buffer(),
 208  *      then push it to the config_item in flush_write_buffer().
 209  *      There is no easy way for us to know if userspace is only doing a partial
 210  *      write, so we don't support them. We expect the entire buffer to come
 211  *      on the first write.
 212  *      Hint: if you're writing a value, first read the file, modify only the
 213  *      the value you're changing, then write entire buffer back.
 214  */
 215
 216 static ssize_t
 217 configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 218 {
 219         struct configfs_buffer * buffer = file->private_data;
 220
 221         down(&buffer->sem);
 222         count = fill_write_buffer(buffer,buf,count);
 223         if (count > 0)
 224                 count = flush_write_buffer(file->f_dentry,buffer,count);
 225         if (count > 0)
 226                 *ppos += count;
 227         up(&buffer->sem);
 228         return count;
 229 }
 230
 231 static int check_perm(struct inode * inode, struct file * file)
 232 {
 233         struct config_item *item = configfs_get_config_item(file->f_dentry->d_parent);
 234         struct configfs_attribute * attr = to_attr(file->f_dentry);
 235         struct configfs_buffer * buffer;
 236         struct configfs_item_operations * ops = NULL;
 237         int error = 0;
 238
 239         if (!item || !attr)
 240                 goto Einval;
 241
 242         /* Grab the module reference for this attribute if we have one */
 243         if (!try_module_get(attr->ca_owner)) {
 244                 error = -ENODEV;
 245                 goto Done;
 246         }
 247
 248         if (item->ci_type)
 249                 ops = item->ci_type->ct_item_ops;
 250         else
 251                 goto Eaccess;
 252
 253         /* File needs write support.
 254          * The inode's perms must say it's ok,
 255          * and we must have a store method.
 256          */
 257         if (file->f_mode & FMODE_WRITE) {
 258
 259                 if (!(inode->i_mode & S_IWUGO) || !ops->store_attribute)
 260                         goto Eaccess;
 261
 262         }
 263
 264         /* File needs read support.
 265          * The inode's perms must say it's ok, and we there
 266          * must be a show method for it.
 267          */
 268         if (file->f_mode & FMODE_READ) {
 269                 if (!(inode->i_mode & S_IRUGO) || !ops->show_attribute)
 270                         goto Eaccess;
 271         }
 272
 273         /* No error? Great, allocate a buffer for the file, and store it
 274          * it in file->private_data for easy access.
 275          */
 276         buffer = kmalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
 277         if (buffer) {
 278                 memset(buffer,0,sizeof(struct configfs_buffer));
 279                 init_MUTEX(&buffer->sem);
 280                 buffer->needs_read_fill = 1;
 281                 buffer->ops = ops;
 282                 file->private_data = buffer;
 283         } else
 284                 error = -ENOMEM;
 285         goto Done;
 286
 287  Einval:
 288         error = -EINVAL;
 289         goto Done;
 290  Eaccess:
 291         error = -EACCES;
 292         module_put(attr->ca_owner);
 293  Done:
 294         if (error && item)
 295                 config_item_put(item);
 296         return error;
 297 }
 298
 299 static int configfs_open_file(struct inode * inode, struct file * filp)
 300 {
 301         return check_perm(inode,filp);
 302 }
 303
 304 static int configfs_release(struct inode * inode, struct file * filp)
 305 {
 306         struct config_item * item = to_item(filp->f_dentry->d_parent);
 307         struct configfs_attribute * attr = to_attr(filp->f_dentry);
 308         struct module * owner = attr->ca_owner;
 309         struct configfs_buffer * buffer = filp->private_data;
 310
 311         if (item)
 312                 config_item_put(item);
 313         /* After this point, attr should not be accessed. */
 314         module_put(owner);
 315
 316         if (buffer) {
 317                 if (buffer->page)
 318                         free_page((unsigned long)buffer->page);
 319                 kfree(buffer);
 320         }
 321         return 0;
 322 }
 323
 324 struct file_operations configfs_file_operations = {
 325         .read           = configfs_read_file,
 326         .write          = configfs_write_file,
 327         .llseek         = generic_file_llseek,
 328         .open           = configfs_open_file,
 329         .release        = configfs_release,
 330 };
 331
 332
 333 int configfs_add_file(struct dentry * dir, const struct configfs_attribute * attr, int type)
 334 {
 335         struct configfs_dirent * parent_sd = dir->d_fsdata;
 336         umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 337         int error = 0;
 338
 339         down(&dir->d_inode->i_sem);
 340         error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 341         up(&dir->d_inode->i_sem);
 342
 343         return error;
 344 }
 345
 346
 347 /**
 348  *      configfs_create_file - create an attribute file for an item.
 349  *      @item:  item we're creating for.
 350  *      @attr:  atrribute descriptor.
 351  */
 352
 353 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 354 {
 355         BUG_ON(!item || !item->ci_dentry || !attr);
 356
 357         return configfs_add_file(item->ci_dentry, attr,
 358                                  CONFIGFS_ITEM_ATTR);
 359 }
 360