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