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 */
fill_read_buffer(struct dentry * dentry,struct configfs_buffer * buffer)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
configfs_read_file(struct file * file,char __user * buf,size_t count,loff_t * ppos)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
fill_write_buffer(struct configfs_buffer * buffer,const char __user * buf,size_t count)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
flush_write_buffer(struct dentry * dentry,struct configfs_buffer * buffer,size_t count)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
configfs_write_file(struct file * file,const char __user * buf,size_t count,loff_t * ppos)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
check_perm(struct inode * inode,struct file * file)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
configfs_open_file(struct inode * inode,struct file * filp)282 static int configfs_open_file(struct inode * inode, struct file * filp)
283 {
284 return check_perm(inode,filp);
285 }
286
configfs_release(struct inode * inode,struct file * filp)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
configfs_add_file(struct dentry * dir,const struct configfs_attribute * attr,int type)317 int 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
configfs_create_file(struct config_item * item,const struct configfs_attribute * attr)337 int 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