linux/fs/configfs/file.c
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   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
  44struct 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 */
  64static 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
 106static ssize_t
 107configfs_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);
 121out:
 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
 137static int
 138fill_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
 169static int
 170flush_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
 197static ssize_t
 198configfs_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, count);
 207        if (len > 0)
 208                *ppos += len;
 209        mutex_unlock(&buffer->mutex);
 210        return len;
 211}
 212
 213static 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
 282static int configfs_open_file(struct inode * inode, struct file * filp)
 283{
 284        return check_perm(inode,filp);
 285}
 286
 287static 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
 308const 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
 317int configfs_add_file(struct dentry * dir, const struct configfs_attribute * attr, int type)
 318{
 319        struct configfs_dirent * parent_sd = dir->d_fsdata;
 320        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 321        int error = 0;
 322
 323        mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_NORMAL);
 324        error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 325        mutex_unlock(&dir->d_inode->i_mutex);
 326
 327        return error;
 328}
 329
 330
 331/**
 332 *      configfs_create_file - create an attribute file for an item.
 333 *      @item:  item we're creating for.
 334 *      @attr:  atrribute descriptor.
 335 */
 336
 337int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 338{
 339        BUG_ON(!item || !item->ci_dentry || !attr);
 340
 341        return configfs_add_file(item->ci_dentry, attr,
 342                                 CONFIGFS_ITEM_ATTR);
 343}
 344
 345
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