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 <linux/mutex.h>
  31 #include <asm/uaccess.h>
  32
  33 #include <linux/configfs.h>
  34 #include "configfs_internal.h"
  35
  36 /*
  37  * A simple attribute can only be 4096 characters.  Why 4k?  Because the
  38  * original code limited it to PAGE_SIZE.  That's a bad idea, though,
  39  * because an attribute of 16k on ia64 won't work on x86.  So we limit to
  40  * 4k, our minimum common page size.
  41  */
  42 #define SIMPLE_ATTR_SIZE 4096
  43
  44 struct configfs_buffer {
  45         size_t                  count;
  46         loff_t                  pos;
  47         char                    * page;
  48         struct configfs_item_operations * ops;
  49         struct mutex            mutex;
  50         int                     needs_read_fill;
  51 };
  52
  53
  54 /**
  55  *      fill_read_buffer - allocate and fill buffer from item.
  56  *      @dentry:        dentry pointer.
  57  *      @buffer:        data buffer for file.
  58  *
  59  *      Allocate @buffer->page, if it hasn't been already, then call the
  60  *      config_item's show() method to fill the buffer with this attribute's
  61  *      data.
  62  *      This is called only once, on the file's first read.
  63  */
  64 static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
  65 {
  66         struct configfs_attribute * attr = to_attr(dentry);
  67         struct config_item * item = to_item(dentry->d_parent);
  68         struct configfs_item_operations * ops = buffer->ops;
  69         int ret = 0;
  70         ssize_t count;
  71
  72         if (!buffer->page)
  73                 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  74         if (!buffer->page)
  75                 return -ENOMEM;
  76
  77         count = ops->show_attribute(item,attr,buffer->page);
  78         buffer->needs_read_fill = 0;
  79         BUG_ON(count > (ssize_t)SIMPLE_ATTR_SIZE);
  80         if (count >= 0)
  81                 buffer->count = count;
  82         else
  83                 ret = count;
  84         return ret;
  85 }
  86
  87 /**
  88  *      configfs_read_file - read an attribute.
  89  *      @file:  file pointer.
  90  *      @buf:   buffer to fill.
  91  *      @count: number of bytes to read.
  92  *      @ppos:  starting offset in file.
  93  *
  94  *      Userspace wants to read an attribute file. The attribute descriptor
  95  *      is in the file's ->d_fsdata. The target item is in the directory's
  96  *      ->d_fsdata.
  97  *
  98  *      We call fill_read_buffer() to allocate and fill the buffer from the
  99  *      item's show() method exactly once (if the read is happening from
 100  *      the beginning of the file). That should fill the entire buffer with
 101  *      all the data the item has to offer for that attribute.
 102  *      We then call flush_read_buffer() to copy the buffer to userspace
 103  *      in the increments specified.
 104  */
 105
 106 static ssize_t
 107 configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 108 {
 109         struct configfs_buffer * buffer = file->private_data;
 110         ssize_t retval = 0;
 111
 112         mutex_lock(&buffer->mutex);
 113         if (buffer->needs_read_fill) {
 114                 if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
 115                         goto out;
 116         }
 117         pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
 118                  __func__, count, *ppos, buffer->page);
 119         retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
 120                                          buffer->count);
 121 out:
 122         mutex_unlock(&buffer->mutex);
 123         return retval;
 124 }
 125
 126
 127 /**
 128  *      fill_write_buffer - copy buffer from userspace.
 129  *      @buffer:        data buffer for file.
 130  *      @buf:           data from user.
 131  *      @count:         number of bytes in @userbuf.
 132  *
 133  *      Allocate @buffer->page if it hasn't been already, then
 134  *      copy the user-supplied buffer into it.
 135  */
 136
 137 static int
 138 fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
 139 {
 140         int error;
 141
 142         if (!buffer->page)
 143                 buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
 144         if (!buffer->page)
 145                 return -ENOMEM;
 146
 147         if (count >= SIMPLE_ATTR_SIZE)
 148                 count = SIMPLE_ATTR_SIZE - 1;
 149         error = copy_from_user(buffer->page,buf,count);
 150         buffer->needs_read_fill = 1;
 151         /* if buf is assumed to contain a string, terminate it by \0,
 152          * so e.g. sscanf() can scan the string easily */
 153         buffer->page[count] = 0;
 154         return error ? -EFAULT : count;
 155 }
 156
 157
 158 /**
 159  *      flush_write_buffer - push buffer to config_item.
 160  *      @dentry:        dentry to the attribute
 161  *      @buffer:        data buffer for file.
 162  *      @count:         number of bytes
 163  *
 164  *      Get the correct pointers for the config_item and the attribute we're
 165  *      dealing with, then call the store() method for the attribute,
 166  *      passing the buffer that we acquired in fill_write_buffer().
 167  */
 168
 169 static int
 170 flush_write_buffer(struct dentry * dentry, struct configfs_buffer * buffer, size_t count)
 171 {
 172         struct configfs_attribute * attr = to_attr(dentry);
 173         struct config_item * item = to_item(dentry->d_parent);
 174         struct configfs_item_operations * ops = buffer->ops;
 175
 176         return ops->store_attribute(item,attr,buffer->page,count);
 177 }
 178
 179
 180 /**
 181  *      configfs_write_file - write an attribute.
 182  *      @file:  file pointer
 183  *      @buf:   data to write
 184  *      @count: number of bytes
 185  *      @ppos:  starting offset
 186  *
 187  *      Similar to configfs_read_file(), though working in the opposite direction.
 188  *      We allocate and fill the data from the user in fill_write_buffer(),
 189  *      then push it to the config_item in flush_write_buffer().
 190  *      There is no easy way for us to know if userspace is only doing a partial
 191  *      write, so we don't support them. We expect the entire buffer to come
 192  *      on the first write.
 193  *      Hint: if you're writing a value, first read the file, modify only the
 194  *      the value you're changing, then write entire buffer back.
 195  */
 196
 197 static ssize_t
 198 configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 199 {
 200         struct configfs_buffer * buffer = file->private_data;
 201         ssize_t len;
 202
 203         mutex_lock(&buffer->mutex);
 204         len = fill_write_buffer(buffer, buf, count);
 205         if (len > 0)
 206                 len = flush_write_buffer(file->f_path.dentry, buffer, len);
 207         if (len > 0)
 208                 *ppos += len;
 209         mutex_unlock(&buffer->mutex);
 210         return len;
 211 }
 212
 213 static int check_perm(struct inode * inode, struct file * file)
 214 {
 215         struct config_item *item = configfs_get_config_item(file->f_path.dentry->d_parent);
 216         struct configfs_attribute * attr = to_attr(file->f_path.dentry);
 217         struct configfs_buffer * buffer;
 218         struct configfs_item_operations * ops = NULL;
 219         int error = 0;
 220
 221         if (!item || !attr)
 222                 goto Einval;
 223
 224         /* Grab the module reference for this attribute if we have one */
 225         if (!try_module_get(attr->ca_owner)) {
 226                 error = -ENODEV;
 227                 goto Done;
 228         }
 229
 230         if (item->ci_type)
 231                 ops = item->ci_type->ct_item_ops;
 232         else
 233                 goto Eaccess;
 234
 235         /* File needs write support.
 236          * The inode's perms must say it's ok,
 237          * and we must have a store method.
 238          */
 239         if (file->f_mode & FMODE_WRITE) {
 240
 241                 if (!(inode->i_mode & S_IWUGO) || !ops->store_attribute)
 242                         goto Eaccess;
 243
 244         }
 245
 246         /* File needs read support.
 247          * The inode's perms must say it's ok, and we there
 248          * must be a show method for it.
 249          */
 250         if (file->f_mode & FMODE_READ) {
 251                 if (!(inode->i_mode & S_IRUGO) || !ops->show_attribute)
 252                         goto Eaccess;
 253         }
 254
 255         /* No error? Great, allocate a buffer for the file, and store it
 256          * it in file->private_data for easy access.
 257          */
 258         buffer = kzalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
 259         if (!buffer) {
 260                 error = -ENOMEM;
 261                 goto Enomem;
 262         }
 263         mutex_init(&buffer->mutex);
 264         buffer->needs_read_fill = 1;
 265         buffer->ops = ops;
 266         file->private_data = buffer;
 267         goto Done;
 268
 269  Einval:
 270         error = -EINVAL;
 271         goto Done;
 272  Eaccess:
 273         error = -EACCES;
 274  Enomem:
 275         module_put(attr->ca_owner);
 276  Done:
 277         if (error && item)
 278                 config_item_put(item);
 279         return error;
 280 }
 281
 282 static int configfs_open_file(struct inode * inode, struct file * filp)
 283 {
 284         return check_perm(inode,filp);
 285 }
 286
 287 static int configfs_release(struct inode * inode, struct file * filp)
 288 {
 289         struct config_item * item = to_item(filp->f_path.dentry->d_parent);
 290         struct configfs_attribute * attr = to_attr(filp->f_path.dentry);
 291         struct module * owner = attr->ca_owner;
 292         struct configfs_buffer * buffer = filp->private_data;
 293
 294         if (item)
 295                 config_item_put(item);
 296         /* After this point, attr should not be accessed. */
 297         module_put(owner);
 298
 299         if (buffer) {
 300                 if (buffer->page)
 301                         free_page((unsigned long)buffer->page);
 302                 mutex_destroy(&buffer->mutex);
 303                 kfree(buffer);
 304         }
 305         return 0;
 306 }
 307
 308 const struct file_operations configfs_file_operations = {
 309         .read           = configfs_read_file,
 310         .write          = configfs_write_file,
 311         .llseek         = generic_file_llseek,
 312         .open           = configfs_open_file,
 313         .release        = configfs_release,
 314 };
 315
 316 /**
 317  *      configfs_create_file - create an attribute file for an item.
 318  *      @item:  item we're creating for.
 319  *      @attr:  atrribute descriptor.
 320  */
 321
 322 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 323 {
 324         struct dentry *dir = item->ci_dentry;
 325         struct configfs_dirent *parent_sd = dir->d_fsdata;
 326         umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 327         int error = 0;
 328
 329         mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_NORMAL);
 330         error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
 331                                      CONFIGFS_ITEM_ATTR);
 332         mutex_unlock(&dir->d_inode->i_mutex);
 333
 334         return error;
 335 }
 336