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/fs/configfs/file.c

https://bitbucket.org/cyanogenmod/android_kernel_asus_tf300t
C | 344 lines | 182 code | 48 blank | 114 comment | 28 complexity | 26439e3c45a90eb51484d98ebd86ff50 MD5 | raw file
Possible License(s): LGPL-2.0, AGPL-1.0, GPL-2.0
  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