Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  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                  __FUNCTION__, 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, count);
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 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 
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 
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