xref: /openbmc/linux/fs/configfs/file.c (revision 87c2ce3b)
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/dnotify.h>
30 #include <linux/slab.h>
31 #include <asm/uaccess.h>
32 #include <asm/semaphore.h>
33 
34 #include <linux/configfs.h>
35 #include "configfs_internal.h"
36 
37 
38 struct configfs_buffer {
39 	size_t			count;
40 	loff_t			pos;
41 	char			* page;
42 	struct configfs_item_operations	* ops;
43 	struct semaphore	sem;
44 	int			needs_read_fill;
45 };
46 
47 
48 /**
49  *	fill_read_buffer - allocate and fill buffer from item.
50  *	@dentry:	dentry pointer.
51  *	@buffer:	data buffer for file.
52  *
53  *	Allocate @buffer->page, if it hasn't been already, then call the
54  *	config_item's show() method to fill the buffer with this attribute's
55  *	data.
56  *	This is called only once, on the file's first read.
57  */
58 static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
59 {
60 	struct configfs_attribute * attr = to_attr(dentry);
61 	struct config_item * item = to_item(dentry->d_parent);
62 	struct configfs_item_operations * ops = buffer->ops;
63 	int ret = 0;
64 	ssize_t count;
65 
66 	if (!buffer->page)
67 		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
68 	if (!buffer->page)
69 		return -ENOMEM;
70 
71 	count = ops->show_attribute(item,attr,buffer->page);
72 	buffer->needs_read_fill = 0;
73 	BUG_ON(count > (ssize_t)PAGE_SIZE);
74 	if (count >= 0)
75 		buffer->count = count;
76 	else
77 		ret = count;
78 	return ret;
79 }
80 
81 
82 /**
83  *	flush_read_buffer - push buffer to userspace.
84  *	@buffer:	data buffer for file.
85  *	@userbuf:	user-passed buffer.
86  *	@count:		number of bytes requested.
87  *	@ppos:		file position.
88  *
89  *	Copy the buffer we filled in fill_read_buffer() to userspace.
90  *	This is done at the reader's leisure, copying and advancing
91  *	the amount they specify each time.
92  *	This may be called continuously until the buffer is empty.
93  */
94 static int flush_read_buffer(struct configfs_buffer * buffer, char __user * buf,
95 			     size_t count, loff_t * ppos)
96 {
97 	int error;
98 
99 	if (*ppos > buffer->count)
100 		return 0;
101 
102 	if (count > (buffer->count - *ppos))
103 		count = buffer->count - *ppos;
104 
105 	error = copy_to_user(buf,buffer->page + *ppos,count);
106 	if (!error)
107 		*ppos += count;
108 	return error ? -EFAULT : count;
109 }
110 
111 /**
112  *	configfs_read_file - read an attribute.
113  *	@file:	file pointer.
114  *	@buf:	buffer to fill.
115  *	@count:	number of bytes to read.
116  *	@ppos:	starting offset in file.
117  *
118  *	Userspace wants to read an attribute file. The attribute descriptor
119  *	is in the file's ->d_fsdata. The target item is in the directory's
120  *	->d_fsdata.
121  *
122  *	We call fill_read_buffer() to allocate and fill the buffer from the
123  *	item's show() method exactly once (if the read is happening from
124  *	the beginning of the file). That should fill the entire buffer with
125  *	all the data the item has to offer for that attribute.
126  *	We then call flush_read_buffer() to copy the buffer to userspace
127  *	in the increments specified.
128  */
129 
130 static ssize_t
131 configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
132 {
133 	struct configfs_buffer * buffer = file->private_data;
134 	ssize_t retval = 0;
135 
136 	down(&buffer->sem);
137 	if (buffer->needs_read_fill) {
138 		if ((retval = fill_read_buffer(file->f_dentry,buffer)))
139 			goto out;
140 	}
141 	pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
142 		 __FUNCTION__,count,*ppos,buffer->page);
143 	retval = flush_read_buffer(buffer,buf,count,ppos);
144 out:
145 	up(&buffer->sem);
146 	return retval;
147 }
148 
149 
150 /**
151  *	fill_write_buffer - copy buffer from userspace.
152  *	@buffer:	data buffer for file.
153  *	@userbuf:	data from user.
154  *	@count:		number of bytes in @userbuf.
155  *
156  *	Allocate @buffer->page if it hasn't been already, then
157  *	copy the user-supplied buffer into it.
158  */
159 
160 static int
161 fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
162 {
163 	int error;
164 
165 	if (!buffer->page)
166 		buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
167 	if (!buffer->page)
168 		return -ENOMEM;
169 
170 	if (count > PAGE_SIZE)
171 		count = PAGE_SIZE;
172 	error = copy_from_user(buffer->page,buf,count);
173 	buffer->needs_read_fill = 1;
174 	return error ? -EFAULT : count;
175 }
176 
177 
178 /**
179  *	flush_write_buffer - push buffer to config_item.
180  *	@file:		file pointer.
181  *	@buffer:	data buffer for file.
182  *
183  *	Get the correct pointers for the config_item and the attribute we're
184  *	dealing with, then call the store() method for the attribute,
185  *	passing the buffer that we acquired in fill_write_buffer().
186  */
187 
188 static int
189 flush_write_buffer(struct dentry * dentry, struct configfs_buffer * buffer, size_t count)
190 {
191 	struct configfs_attribute * attr = to_attr(dentry);
192 	struct config_item * item = to_item(dentry->d_parent);
193 	struct configfs_item_operations * ops = buffer->ops;
194 
195 	return ops->store_attribute(item,attr,buffer->page,count);
196 }
197 
198 
199 /**
200  *	configfs_write_file - write an attribute.
201  *	@file:	file pointer
202  *	@buf:	data to write
203  *	@count:	number of bytes
204  *	@ppos:	starting offset
205  *
206  *	Similar to configfs_read_file(), though working in the opposite direction.
207  *	We allocate and fill the data from the user in fill_write_buffer(),
208  *	then push it to the config_item in flush_write_buffer().
209  *	There is no easy way for us to know if userspace is only doing a partial
210  *	write, so we don't support them. We expect the entire buffer to come
211  *	on the first write.
212  *	Hint: if you're writing a value, first read the file, modify only the
213  *	the value you're changing, then write entire buffer back.
214  */
215 
216 static ssize_t
217 configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
218 {
219 	struct configfs_buffer * buffer = file->private_data;
220 
221 	down(&buffer->sem);
222 	count = fill_write_buffer(buffer,buf,count);
223 	if (count > 0)
224 		count = flush_write_buffer(file->f_dentry,buffer,count);
225 	if (count > 0)
226 		*ppos += count;
227 	up(&buffer->sem);
228 	return count;
229 }
230 
231 static int check_perm(struct inode * inode, struct file * file)
232 {
233 	struct config_item *item = configfs_get_config_item(file->f_dentry->d_parent);
234 	struct configfs_attribute * attr = to_attr(file->f_dentry);
235 	struct configfs_buffer * buffer;
236 	struct configfs_item_operations * ops = NULL;
237 	int error = 0;
238 
239 	if (!item || !attr)
240 		goto Einval;
241 
242 	/* Grab the module reference for this attribute if we have one */
243 	if (!try_module_get(attr->ca_owner)) {
244 		error = -ENODEV;
245 		goto Done;
246 	}
247 
248 	if (item->ci_type)
249 		ops = item->ci_type->ct_item_ops;
250 	else
251 		goto Eaccess;
252 
253 	/* File needs write support.
254 	 * The inode's perms must say it's ok,
255 	 * and we must have a store method.
256 	 */
257 	if (file->f_mode & FMODE_WRITE) {
258 
259 		if (!(inode->i_mode & S_IWUGO) || !ops->store_attribute)
260 			goto Eaccess;
261 
262 	}
263 
264 	/* File needs read support.
265 	 * The inode's perms must say it's ok, and we there
266 	 * must be a show method for it.
267 	 */
268 	if (file->f_mode & FMODE_READ) {
269 		if (!(inode->i_mode & S_IRUGO) || !ops->show_attribute)
270 			goto Eaccess;
271 	}
272 
273 	/* No error? Great, allocate a buffer for the file, and store it
274 	 * it in file->private_data for easy access.
275 	 */
276 	buffer = kmalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
277 	if (buffer) {
278 		memset(buffer,0,sizeof(struct configfs_buffer));
279 		init_MUTEX(&buffer->sem);
280 		buffer->needs_read_fill = 1;
281 		buffer->ops = ops;
282 		file->private_data = buffer;
283 	} else
284 		error = -ENOMEM;
285 	goto Done;
286 
287  Einval:
288 	error = -EINVAL;
289 	goto Done;
290  Eaccess:
291 	error = -EACCES;
292 	module_put(attr->ca_owner);
293  Done:
294 	if (error && item)
295 		config_item_put(item);
296 	return error;
297 }
298 
299 static int configfs_open_file(struct inode * inode, struct file * filp)
300 {
301 	return check_perm(inode,filp);
302 }
303 
304 static int configfs_release(struct inode * inode, struct file * filp)
305 {
306 	struct config_item * item = to_item(filp->f_dentry->d_parent);
307 	struct configfs_attribute * attr = to_attr(filp->f_dentry);
308 	struct module * owner = attr->ca_owner;
309 	struct configfs_buffer * buffer = filp->private_data;
310 
311 	if (item)
312 		config_item_put(item);
313 	/* After this point, attr should not be accessed. */
314 	module_put(owner);
315 
316 	if (buffer) {
317 		if (buffer->page)
318 			free_page((unsigned long)buffer->page);
319 		kfree(buffer);
320 	}
321 	return 0;
322 }
323 
324 struct file_operations configfs_file_operations = {
325 	.read		= configfs_read_file,
326 	.write		= configfs_write_file,
327 	.llseek		= generic_file_llseek,
328 	.open		= configfs_open_file,
329 	.release	= configfs_release,
330 };
331 
332 
333 int configfs_add_file(struct dentry * dir, const struct configfs_attribute * attr, int type)
334 {
335 	struct configfs_dirent * parent_sd = dir->d_fsdata;
336 	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
337 	int error = 0;
338 
339 	mutex_lock(&dir->d_inode->i_mutex);
340 	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
341 	mutex_unlock(&dir->d_inode->i_mutex);
342 
343 	return error;
344 }
345 
346 
347 /**
348  *	configfs_create_file - create an attribute file for an item.
349  *	@item:	item we're creating for.
350  *	@attr:	atrribute descriptor.
351  */
352 
353 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
354 {
355 	BUG_ON(!item || !item->ci_dentry || !attr);
356 
357 	return configfs_add_file(item->ci_dentry, attr,
358 				 CONFIGFS_ITEM_ATTR);
359 }
360 
361