1/*
2 * Resizable simple ram filesystem for Linux.
3 *
4 * Copyright (C) 2000 Linus Torvalds.
5 * 2000 Transmeta Corp.
6 *
7 * Usage limits added by David Gibson, Linuxcare Australia.
8 * This file is released under the GPL.
9 */
10
11/*
12 * NOTE! This filesystem is probably most useful
13 * not as a real filesystem, but as an example of
14 * how virtual filesystems can be written.
15 *
16 * It doesn't get much simpler than this. Consider
17 * that this file implements the full semantics of
18 * a POSIX-compliant read-write filesystem.
19 *
20 * Note in particular how the filesystem does not
21 * need to implement any data structures of its own
22 * to keep track of the virtual data: using the VFS
23 * caches is sufficient.
24 */
25
26#include <linux/fs.h>
27#include <linux/pagemap.h>
28#include <linux/highmem.h>
29#include <linux/time.h>
30#include <linux/init.h>
31#include <linux/string.h>
32#include <linux/backing-dev.h>
33#include <linux/ramfs.h>
34#include <linux/sched.h>
35#include <linux/parser.h>
36#include <linux/magic.h>
37#include <linux/slab.h>
38#include <linux/uaccess.h>
39#include <linux/fs_context.h>
40#include <linux/fs_parser.h>
41#include <linux/seq_file.h>
42#include "internal.h"
43
44struct ramfs_mount_opts {
45 umode_t mode;
46};
47
48struct ramfs_fs_info {
49 struct ramfs_mount_opts mount_opts;
50};
51
52#define RAMFS_DEFAULT_MODE 0755
53
54static const struct super_operations ramfs_ops;
55static const struct inode_operations ramfs_dir_inode_operations;
56
57struct inode *ramfs_get_inode(struct super_block *sb,
58 const struct inode *dir, umode_t mode, dev_t dev)
59{
60 struct inode * inode = new_inode(sb);
61
62 if (inode) {
63 inode->i_ino = get_next_ino();
64 inode_init_owner(idmap: &nop_mnt_idmap, inode, dir, mode);
65 inode->i_mapping->a_ops = &ram_aops;
66 mapping_set_gfp_mask(m: inode->i_mapping, GFP_HIGHUSER);
67 mapping_set_unevictable(mapping: inode->i_mapping);
68 simple_inode_init_ts(inode);
69 switch (mode & S_IFMT) {
70 default:
71 init_special_inode(inode, mode, dev);
72 break;
73 case S_IFREG:
74 inode->i_op = &ramfs_file_inode_operations;
75 inode->i_fop = &ramfs_file_operations;
76 break;
77 case S_IFDIR:
78 inode->i_op = &ramfs_dir_inode_operations;
79 inode->i_fop = &simple_dir_operations;
80
81 /* directory inodes start off with i_nlink == 2 (for "." entry) */
82 inc_nlink(inode);
83 break;
84 case S_IFLNK:
85 inode->i_op = &page_symlink_inode_operations;
86 inode_nohighmem(inode);
87 break;
88 }
89 }
90 return inode;
91}
92
93/*
94 * File creation. Allocate an inode, and we're done..
95 */
96/* SMP-safe */
97static int
98ramfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
99 struct dentry *dentry, umode_t mode, dev_t dev)
100{
101 struct inode * inode = ramfs_get_inode(sb: dir->i_sb, dir, mode, dev);
102 int error = -ENOSPC;
103
104 if (inode) {
105 error = security_inode_init_security(inode, dir,
106 qstr: &dentry->d_name, NULL,
107 NULL);
108 if (error) {
109 iput(inode);
110 goto out;
111 }
112
113 d_make_persistent(dentry, inode);
114 error = 0;
115 inode_set_mtime_to_ts(inode: dir, ts: inode_set_ctime_current(inode: dir));
116 }
117out:
118 return error;
119}
120
121static struct dentry *ramfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
122 struct dentry *dentry, umode_t mode)
123{
124 int retval = ramfs_mknod(idmap: &nop_mnt_idmap, dir, dentry, mode: mode | S_IFDIR, dev: 0);
125 if (!retval)
126 inc_nlink(inode: dir);
127 return ERR_PTR(error: retval);
128}
129
130static int ramfs_create(struct mnt_idmap *idmap, struct inode *dir,
131 struct dentry *dentry, umode_t mode, bool excl)
132{
133 return ramfs_mknod(idmap: &nop_mnt_idmap, dir, dentry, mode: mode | S_IFREG, dev: 0);
134}
135
136static int ramfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
137 struct dentry *dentry, const char *symname)
138{
139 struct inode *inode;
140 int error = -ENOSPC;
141
142 inode = ramfs_get_inode(sb: dir->i_sb, dir, S_IFLNK|S_IRWXUGO, dev: 0);
143 if (inode) {
144 int l = strlen(symname)+1;
145
146 error = security_inode_init_security(inode, dir,
147 qstr: &dentry->d_name, NULL,
148 NULL);
149 if (error) {
150 iput(inode);
151 goto out;
152 }
153
154 error = page_symlink(inode, symname, len: l);
155 if (!error) {
156 d_make_persistent(dentry, inode);
157 inode_set_mtime_to_ts(inode: dir,
158 ts: inode_set_ctime_current(inode: dir));
159 } else
160 iput(inode);
161 }
162out:
163 return error;
164}
165
166static int ramfs_tmpfile(struct mnt_idmap *idmap,
167 struct inode *dir, struct file *file, umode_t mode)
168{
169 struct inode *inode;
170 int error;
171
172 inode = ramfs_get_inode(sb: dir->i_sb, dir, mode, dev: 0);
173 if (!inode)
174 return -ENOSPC;
175
176 error = security_inode_init_security(inode, dir,
177 qstr: &file_dentry(file)->d_name, NULL,
178 NULL);
179 if (error) {
180 iput(inode);
181 goto out;
182 }
183
184 d_tmpfile(file, inode);
185out:
186 return finish_open_simple(file, error);
187}
188
189static const struct inode_operations ramfs_dir_inode_operations = {
190 .create = ramfs_create,
191 .lookup = simple_lookup,
192 .link = simple_link,
193 .unlink = simple_unlink,
194 .symlink = ramfs_symlink,
195 .mkdir = ramfs_mkdir,
196 .rmdir = simple_rmdir,
197 .mknod = ramfs_mknod,
198 .rename = simple_rename,
199 .tmpfile = ramfs_tmpfile,
200};
201
202/*
203 * Display the mount options in /proc/mounts.
204 */
205static int ramfs_show_options(struct seq_file *m, struct dentry *root)
206{
207 struct ramfs_fs_info *fsi = root->d_sb->s_fs_info;
208
209 if (fsi->mount_opts.mode != RAMFS_DEFAULT_MODE)
210 seq_printf(m, fmt: ",mode=%o", fsi->mount_opts.mode);
211 return 0;
212}
213
214static const struct super_operations ramfs_ops = {
215 .statfs = simple_statfs,
216 .drop_inode = inode_just_drop,
217 .show_options = ramfs_show_options,
218};
219
220enum ramfs_param {
221 Opt_mode,
222};
223
224const struct fs_parameter_spec ramfs_fs_parameters[] = {
225 fsparam_u32oct("mode", Opt_mode),
226 {}
227};
228
229static int ramfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
230{
231 struct fs_parse_result result;
232 struct ramfs_fs_info *fsi = fc->s_fs_info;
233 int opt;
234
235 opt = fs_parse(fc, desc: ramfs_fs_parameters, param, result: &result);
236 if (opt == -ENOPARAM) {
237 opt = vfs_parse_fs_param_source(fc, param);
238 if (opt != -ENOPARAM)
239 return opt;
240 /*
241 * We might like to report bad mount options here;
242 * but traditionally ramfs has ignored all mount options,
243 * and as it is used as a !CONFIG_SHMEM simple substitute
244 * for tmpfs, better continue to ignore other mount options.
245 */
246 return 0;
247 }
248 if (opt < 0)
249 return opt;
250
251 switch (opt) {
252 case Opt_mode:
253 fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
254 break;
255 }
256
257 return 0;
258}
259
260static int ramfs_fill_super(struct super_block *sb, struct fs_context *fc)
261{
262 struct ramfs_fs_info *fsi = sb->s_fs_info;
263 struct inode *inode;
264
265 sb->s_maxbytes = MAX_LFS_FILESIZE;
266 sb->s_blocksize = PAGE_SIZE;
267 sb->s_blocksize_bits = PAGE_SHIFT;
268 sb->s_magic = RAMFS_MAGIC;
269 sb->s_op = &ramfs_ops;
270 sb->s_d_flags = DCACHE_DONTCACHE;
271 sb->s_time_gran = 1;
272
273 inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, dev: 0);
274 sb->s_root = d_make_root(inode);
275 if (!sb->s_root)
276 return -ENOMEM;
277
278 return 0;
279}
280
281static int ramfs_get_tree(struct fs_context *fc)
282{
283 return get_tree_nodev(fc, fill_super: ramfs_fill_super);
284}
285
286static void ramfs_free_fc(struct fs_context *fc)
287{
288 kfree(objp: fc->s_fs_info);
289}
290
291static const struct fs_context_operations ramfs_context_ops = {
292 .free = ramfs_free_fc,
293 .parse_param = ramfs_parse_param,
294 .get_tree = ramfs_get_tree,
295};
296
297int ramfs_init_fs_context(struct fs_context *fc)
298{
299 struct ramfs_fs_info *fsi;
300
301 fsi = kzalloc(sizeof(*fsi), GFP_KERNEL);
302 if (!fsi)
303 return -ENOMEM;
304
305 fsi->mount_opts.mode = RAMFS_DEFAULT_MODE;
306 fc->s_fs_info = fsi;
307 fc->ops = &ramfs_context_ops;
308 return 0;
309}
310
311void ramfs_kill_sb(struct super_block *sb)
312{
313 kfree(objp: sb->s_fs_info);
314 kill_anon_super(sb);
315}
316
317static struct file_system_type ramfs_fs_type = {
318 .name = "ramfs",
319 .init_fs_context = ramfs_init_fs_context,
320 .parameters = ramfs_fs_parameters,
321 .kill_sb = ramfs_kill_sb,
322 .fs_flags = FS_USERNS_MOUNT,
323};
324
325static int __init init_ramfs_fs(void)
326{
327 return register_filesystem(&ramfs_fs_type);
328}
329fs_initcall(init_ramfs_fs);
330

source code of linux/fs/ramfs/inode.c