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/slab.h>
  30 #include <asm/uaccess.h>
  31 #include <asm/semaphore.h>
  32
  33 #include <linux/configfs.h>
  34 #include "configfs_internal.h"
  35
  36
  37 struct configfs_buffer {
  38         size_t                  count;
  39         loff_t                  pos;
  40         char                    * page;
  41         struct configfs_item_operations * ops;
  42         struct semaphore        sem;
  43         int                     needs_read_fill;
  44 };
  45
  46
  47 /**
  48  *      fill_read_buffer - allocate and fill buffer from item.
  49  *      @dentry:        dentry pointer.
  50  *      @buffer:        data buffer for file.
  51  *
  52  *      Allocate @buffer->page, if it hasn't been already, then call the
  53  *      config_item's show() method to fill the buffer with this attribute's
  54  *      data.
  55  *      This is called only once, on the file's first read.
  56  */
  57 static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
  58 {
  59         struct configfs_attribute * attr = to_attr(dentry);
  60         struct config_item * item = to_item(dentry->d_parent);
  61         struct configfs_item_operations * ops = buffer->ops;
  62         int ret = 0;
  63         ssize_t count;
  64
  65         if (!buffer->page)
  66                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  67         if (!buffer->page)
  68                 return -ENOMEM;
  69
  70         count = ops->show_attribute(item,attr,buffer->page);
  71         buffer->needs_read_fill = 0;
  72         BUG_ON(count > (ssize_t)PAGE_SIZE);
  73         if (count >= 0)
  74                 buffer->count = count;
  75         else
  76                 ret = count;
  77         return ret;
  78 }
  79
  80
  81 /**
  82  *      flush_read_buffer - push buffer to userspace.
  83  *      @buffer:        data buffer for file.
  84  *      @userbuf:       user-passed buffer.
  85  *      @count:         number of bytes requested.
  86  *      @ppos:          file position.
  87  *
  88  *      Copy the buffer we filled in fill_read_buffer() to userspace.
  89  *      This is done at the reader's leisure, copying and advancing
  90  *      the amount they specify each time.
  91  *      This may be called continuously until the buffer is empty.
  92  */
  93 static int flush_read_buffer(struct configfs_buffer * buffer, char __user * buf,
  94                              size_t count, loff_t * ppos)
  95 {
  96         int error;
  97
  98         if (*ppos > buffer->count)
  99                 return 0;
 100
 101         if (count > (buffer->count - *ppos))
 102                 count = buffer->count - *ppos;
 103
 104         error = copy_to_user(buf,buffer->page + *ppos,count);
 105         if (!error)
 106                 *ppos += count;
 107         return error ? -EFAULT : count;
 108 }
 109
 110 /**
 111  *      configfs_read_file - read an attribute.
 112  *      @file:  file pointer.
 113  *      @buf:   buffer to fill.
 114  *      @count: number of bytes to read.
 115  *      @ppos:  starting offset in file.
 116  *
 117  *      Userspace wants to read an attribute file. The attribute descriptor
 118  *      is in the file's ->d_fsdata. The target item is in the directory's
 119  *      ->d_fsdata.
 120  *
 121  *      We call fill_read_buffer() to allocate and fill the buffer from the
 122  *      item's show() method exactly once (if the read is happening from
 123  *      the beginning of the file). That should fill the entire buffer with
 124  *      all the data the item has to offer for that attribute.
 125  *      We then call flush_read_buffer() to copy the buffer to userspace
 126  *      in the increments specified.
 127  */
 128
 129 static ssize_t
 130 configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 131 {
 132         struct configfs_buffer * buffer = file->private_data;
 133         ssize_t retval = 0;
 134
 135         down(&buffer->sem);
 136         if (buffer->needs_read_fill) {
 137                 if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
 138                         goto out;
 139         }
 140         pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
 141                  __FUNCTION__, count, *ppos, buffer->page);
 142         retval = flush_read_buffer(buffer,buf,count,ppos);
 143 out:
 144         up(&buffer->sem);
 145         return retval;
 146 }
 147
 148
 149 /**
 150  *      fill_write_buffer - copy buffer from userspace.
 151  *      @buffer:        data buffer for file.
 152  *      @buf:           data from user.
 153  *      @count:         number of bytes in @userbuf.
 154  *
 155  *      Allocate @buffer->page if it hasn't been already, then
 156  *      copy the user-supplied buffer into it.
 157  */
 158
 159 static int
 160 fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
 161 {
 162         int error;
 163
 164         if (!buffer->page)
 165                 buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
 166         if (!buffer->page)
 167                 return -ENOMEM;
 168
 169         if (count >= PAGE_SIZE)
 170                 count = PAGE_SIZE - 1;
 171         error = copy_from_user(buffer->page,buf,count);
 172         buffer->needs_read_fill = 1;
 173         /* if buf is assumed to contain a string, terminate it by \0,
 174          * so e.g. sscanf() can scan the string easily */
 175         buffer->page[count] = 0;
 176         return error ? -EFAULT : count;
 177 }
 178
 179
 180 /**
 181  *      flush_write_buffer - push buffer to config_item.
 182  *      @dentry:        dentry to the attribute
 183  *      @buffer:        data buffer for file.
 184  *      @count:         number of bytes
 185  *
 186  *      Get the correct pointers for the config_item and the attribute we're
 187  *      dealing with, then call the store() method for the attribute,
 188  *      passing the buffer that we acquired in fill_write_buffer().
 189  */
 190
 191 static int
 192 flush_write_buffer(struct dentry * dentry, struct configfs_buffer * buffer, size_t count)
 193 {
 194         struct configfs_attribute * attr = to_attr(dentry);
 195         struct config_item * item = to_item(dentry->d_parent);
 196         struct configfs_item_operations * ops = buffer->ops;
 197
 198         return ops->store_attribute(item,attr,buffer->page,count);
 199 }
 200
 201
 202 /**
 203  *      configfs_write_file - write an attribute.
 204  *      @file:  file pointer
 205  *      @buf:   data to write
 206  *      @count: number of bytes
 207  *      @ppos:  starting offset
 208  *
 209  *      Similar to configfs_read_file(), though working in the opposite direction.
 210  *      We allocate and fill the data from the user in fill_write_buffer(),
 211  *      then push it to the config_item in flush_write_buffer().
 212  *      There is no easy way for us to know if userspace is only doing a partial
 213  *      write, so we don't support them. We expect the entire buffer to come
 214  *      on the first write.
 215  *      Hint: if you're writing a value, first read the file, modify only the
 216  *      the value you're changing, then write entire buffer back.
 217  */
 218
 219 static ssize_t
 220 configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 221 {
 222         struct configfs_buffer * buffer = file->private_data;
 223         ssize_t len;
 224
 225         down(&buffer->sem);
 226         len = fill_write_buffer(buffer, buf, count);
 227         if (len > 0)
 228                 len = flush_write_buffer(file->f_path.dentry, buffer, count);
 229         if (len > 0)
 230                 *ppos += len;
 231         up(&buffer->sem);
 232         return len;
 233 }
 234
 235 static int check_perm(struct inode * inode, struct file * file)
 236 {
 237         struct config_item *item = configfs_get_config_item(file->f_path.dentry->d_parent);
 238         struct configfs_attribute * attr = to_attr(file->f_path.dentry);
 239         struct configfs_buffer * buffer;
 240         struct configfs_item_operations * ops = NULL;
 241         int error = 0;
 242
 243         if (!item || !attr)
 244                 goto Einval;
 245
 246         /* Grab the module reference for this attribute if we have one */
 247         if (!try_module_get(attr->ca_owner)) {
 248                 error = -ENODEV;
 249                 goto Done;
 250         }
 251
 252         if (item->ci_type)
 253                 ops = item->ci_type->ct_item_ops;
 254         else
 255                 goto Eaccess;
 256
 257         /* File needs write support.
 258          * The inode's perms must say it's ok,
 259          * and we must have a store method.
 260          */
 261         if (file->f_mode & FMODE_WRITE) {
 262
 263                 if (!(inode->i_mode & S_IWUGO) || !ops->store_attribute)
 264                         goto Eaccess;
 265
 266         }
 267
 268         /* File needs read support.
 269          * The inode's perms must say it's ok, and we there
 270          * must be a show method for it.
 271          */
 272         if (file->f_mode & FMODE_READ) {
 273                 if (!(inode->i_mode & S_IRUGO) || !ops->show_attribute)
 274                         goto Eaccess;
 275         }
 276
 277         /* No error? Great, allocate a buffer for the file, and store it
 278          * it in file->private_data for easy access.
 279          */
 280         buffer = kzalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
 281         if (!buffer) {
 282                 error = -ENOMEM;
 283                 goto Enomem;
 284         }
 285         init_MUTEX(&buffer->sem);
 286         buffer->needs_read_fill = 1;
 287         buffer->ops = ops;
 288         file->private_data = buffer;
 289         goto Done;
 290
 291  Einval:
 292         error = -EINVAL;
 293         goto Done;
 294  Eaccess:
 295         error = -EACCES;
 296  Enomem:
 297         module_put(attr->ca_owner);
 298  Done:
 299         if (error && item)
 300                 config_item_put(item);
 301         return error;
 302 }
 303
 304 static int configfs_open_file(struct inode * inode, struct file * filp)
 305 {
 306         return check_perm(inode,filp);
 307 }
 308
 309 static int configfs_release(struct inode * inode, struct file * filp)
 310 {
 311         struct config_item * item = to_item(filp->f_path.dentry->d_parent);
 312         struct configfs_attribute * attr = to_attr(filp->f_path.dentry);
 313         struct module * owner = attr->ca_owner;
 314         struct configfs_buffer * buffer = filp->private_data;
 315
 316         if (item)
 317                 config_item_put(item);
 318         /* After this point, attr should not be accessed. */
 319         module_put(owner);
 320
 321         if (buffer) {
 322                 if (buffer->page)
 323                         free_page((unsigned long)buffer->page);
 324                 kfree(buffer);
 325         }
 326         return 0;
 327 }
 328
 329 const struct file_operations configfs_file_operations = {
 330         .read           = configfs_read_file,
 331         .write          = configfs_write_file,
 332         .llseek         = generic_file_llseek,
 333         .open           = configfs_open_file,
 334         .release        = configfs_release,
 335 };
 336
 337
 338 int configfs_add_file(struct dentry * dir, const struct configfs_attribute * attr, int type)
 339 {
 340         struct configfs_dirent * parent_sd = dir->d_fsdata;
 341         umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 342         int error = 0;
 343
 344         mutex_lock(&dir->d_inode->i_mutex);
 345         error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 346         mutex_unlock(&dir->d_inode->i_mutex);
 347
 348         return error;
 349 }
 350
 351
 352 /**
 353  *      configfs_create_file - create an attribute file for an item.
 354  *      @item:  item we're creating for.
 355  *      @attr:  atrribute descriptor.
 356  */
 357
 358 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 359 {
 360         BUG_ON(!item || !item->ci_dentry || !attr);
 361
 362         return configfs_add_file(item->ci_dentry, attr,
 363                                  CONFIGFS_ITEM_ATTR);
 364 }
 365