File: /usr/src/linux/fs/ramfs/inode.c
1 /*
2 * Resizable simple ram filesystem for Linux.
3 *
4 * Copyright (C) 2000 Linus Torvalds.
5 * 2000 Transmeta Corp.
6 *
7 * This file is released under the GPL.
8 */
9
10 /*
11 * NOTE! This filesystem is probably most useful
12 * not as a real filesystem, but as an example of
13 * how virtual filesystems can be written.
14 *
15 * It doesn't get much simpler than this. Consider
16 * that this file implements the full semantics of
17 * a POSIX-compliant read-write filesystem.
18 *
19 * Note in particular how the filesystem does not
20 * need to implement any data structures of its own
21 * to keep track of the virtual data: using the VFS
22 * caches is sufficient.
23 */
24
25 #include <linux/module.h>
26 #include <linux/fs.h>
27 #include <linux/pagemap.h>
28 #include <linux/init.h>
29 #include <linux/string.h>
30 #include <linux/locks.h>
31
32 #include <asm/uaccess.h>
33
34 /* some random number */
35 #define RAMFS_MAGIC 0x858458f6
36
37 static struct super_operations ramfs_ops;
38 static struct address_space_operations ramfs_aops;
39 static struct file_operations ramfs_dir_operations;
40 static struct file_operations ramfs_file_operations;
41 static struct inode_operations ramfs_dir_inode_operations;
42
43 static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
44 {
45 buf->f_type = RAMFS_MAGIC;
46 buf->f_bsize = PAGE_CACHE_SIZE;
47 buf->f_namelen = 255;
48 return 0;
49 }
50
51 /*
52 * Lookup the data. This is trivial - if the dentry didn't already
53 * exist, we know it is negative.
54 */
55 static struct dentry * ramfs_lookup(struct inode *dir, struct dentry *dentry)
56 {
57 d_add(dentry, NULL);
58 return NULL;
59 }
60
61 /*
62 * Read a page. Again trivial. If it didn't already exist
63 * in the page cache, it is zero-filled.
64 */
65 static int ramfs_readpage(struct file *file, struct page * page)
66 {
67 if (!Page_Uptodate(page)) {
68 memset(kmap(page), 0, PAGE_CACHE_SIZE);
69 kunmap(page);
70 flush_dcache_page(page);
71 SetPageUptodate(page);
72 }
73 UnlockPage(page);
74 return 0;
75 }
76
77 /*
78 * Writing: just make sure the page gets marked dirty, so that
79 * the page stealer won't grab it.
80 */
81 static int ramfs_writepage(struct page *page)
82 {
83 SetPageDirty(page);
84 UnlockPage(page);
85 return 0;
86 }
87
88 static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
89 {
90 void *addr = kmap(page);
91 if (!Page_Uptodate(page)) {
92 memset(addr, 0, PAGE_CACHE_SIZE);
93 flush_dcache_page(page);
94 SetPageUptodate(page);
95 }
96 SetPageDirty(page);
97 return 0;
98 }
99
100 static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
101 {
102 struct inode *inode = page->mapping->host;
103 loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
104
105 kunmap(page);
106 if (pos > inode->i_size)
107 inode->i_size = pos;
108 return 0;
109 }
110
111 struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
112 {
113 struct inode * inode = new_inode(sb);
114
115 if (inode) {
116 inode->i_mode = mode;
117 inode->i_uid = current->fsuid;
118 inode->i_gid = current->fsgid;
119 inode->i_blksize = PAGE_CACHE_SIZE;
120 inode->i_blocks = 0;
121 inode->i_rdev = NODEV;
122 inode->i_mapping->a_ops = &ramfs_aops;
123 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
124 switch (mode & S_IFMT) {
125 default:
126 init_special_inode(inode, mode, dev);
127 break;
128 case S_IFREG:
129 inode->i_fop = &ramfs_file_operations;
130 break;
131 case S_IFDIR:
132 inode->i_op = &ramfs_dir_inode_operations;
133 inode->i_fop = &ramfs_dir_operations;
134 break;
135 case S_IFLNK:
136 inode->i_op = &page_symlink_inode_operations;
137 break;
138 }
139 }
140 return inode;
141 }
142
143 /*
144 * File creation. Allocate an inode, and we're done..
145 */
146 static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
147 {
148 struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
149 int error = -ENOSPC;
150
151 if (inode) {
152 d_instantiate(dentry, inode);
153 dget(dentry); /* Extra count - pin the dentry in core */
154 error = 0;
155 }
156 return error;
157 }
158
159 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
160 {
161 return ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
162 }
163
164 static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode)
165 {
166 return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
167 }
168
169 /*
170 * Link a file..
171 */
172 static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
173 {
174 struct inode *inode = old_dentry->d_inode;
175
176 if (S_ISDIR(inode->i_mode))
177 return -EPERM;
178
179 inode->i_nlink++;
180 atomic_inc(&inode->i_count); /* New dentry reference */
181 dget(dentry); /* Extra pinning count for the created dentry */
182 d_instantiate(dentry, inode);
183 return 0;
184 }
185
186 static inline int ramfs_positive(struct dentry *dentry)
187 {
188 return dentry->d_inode && !d_unhashed(dentry);
189 }
190
191 /*
192 * Check that a directory is empty (this works
193 * for regular files too, they'll just always be
194 * considered empty..).
195 *
196 * Note that an empty directory can still have
197 * children, they just all have to be negative..
198 */
199 static int ramfs_empty(struct dentry *dentry)
200 {
201 struct list_head *list;
202
203 spin_lock(&dcache_lock);
204 list = dentry->d_subdirs.next;
205
206 while (list != &dentry->d_subdirs) {
207 struct dentry *de = list_entry(list, struct dentry, d_child);
208
209 if (ramfs_positive(de)) {
210 spin_unlock(&dcache_lock);
211 return 0;
212 }
213 list = list->next;
214 }
215 spin_unlock(&dcache_lock);
216 return 1;
217 }
218
219 /*
220 * This works for both directories and regular files.
221 * (non-directories will always have empty subdirs)
222 */
223 static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
224 {
225 int retval = -ENOTEMPTY;
226
227 if (ramfs_empty(dentry)) {
228 struct inode *inode = dentry->d_inode;
229
230 inode->i_nlink--;
231 dput(dentry); /* Undo the count from "create" - this does all the work */
232 retval = 0;
233 }
234 return retval;
235 }
236
237 #define ramfs_rmdir ramfs_unlink
238
239 /*
240 * The VFS layer already does all the dentry stuff for rename,
241 * we just have to decrement the usage count for the target if
242 * it exists so that the VFS layer correctly free's it when it
243 * gets overwritten.
244 */
245 static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
246 {
247 int error = -ENOTEMPTY;
248
249 if (ramfs_empty(new_dentry)) {
250 struct inode *inode = new_dentry->d_inode;
251 if (inode) {
252 inode->i_nlink--;
253 dput(new_dentry);
254 }
255 error = 0;
256 }
257 return error;
258 }
259
260 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
261 {
262 int error;
263
264 error = ramfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
265 if (!error) {
266 int l = strlen(symname)+1;
267 struct inode *inode = dentry->d_inode;
268 error = block_symlink(inode, symname, l);
269 }
270 return error;
271 }
272
273 static int ramfs_sync_file(struct file * file, struct dentry *dentry, int datasync)
274 {
275 return 0;
276 }
277
278 static struct address_space_operations ramfs_aops = {
279 readpage: ramfs_readpage,
280 writepage: ramfs_writepage,
281 prepare_write: ramfs_prepare_write,
282 commit_write: ramfs_commit_write
283 };
284
285 static struct file_operations ramfs_file_operations = {
286 read: generic_file_read,
287 write: generic_file_write,
288 mmap: generic_file_mmap,
289 fsync: ramfs_sync_file,
290 };
291
292 static struct file_operations ramfs_dir_operations = {
293 read: generic_read_dir,
294 readdir: dcache_readdir,
295 fsync: ramfs_sync_file,
296 };
297
298 static struct inode_operations ramfs_dir_inode_operations = {
299 create: ramfs_create,
300 lookup: ramfs_lookup,
301 link: ramfs_link,
302 unlink: ramfs_unlink,
303 symlink: ramfs_symlink,
304 mkdir: ramfs_mkdir,
305 rmdir: ramfs_rmdir,
306 mknod: ramfs_mknod,
307 rename: ramfs_rename,
308 };
309
310 static struct super_operations ramfs_ops = {
311 statfs: ramfs_statfs,
312 put_inode: force_delete,
313 };
314
315 static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
316 {
317 struct inode * inode;
318 struct dentry * root;
319
320 sb->s_blocksize = PAGE_CACHE_SIZE;
321 sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
322 sb->s_magic = RAMFS_MAGIC;
323 sb->s_op = &ramfs_ops;
324 inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
325 if (!inode)
326 return NULL;
327
328 root = d_alloc_root(inode);
329 if (!root) {
330 iput(inode);
331 return NULL;
332 }
333 sb->s_root = root;
334 return sb;
335 }
336
337 static DECLARE_FSTYPE(ramfs_fs_type, "ramfs", ramfs_read_super, FS_LITTER);
338
339 static int __init init_ramfs_fs(void)
340 {
341 return register_filesystem(&ramfs_fs_type);
342 }
343
344 static void __exit exit_ramfs_fs(void)
345 {
346 unregister_filesystem(&ramfs_fs_type);
347 }
348
349 module_init(init_ramfs_fs)
350 module_exit(exit_ramfs_fs)
351