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 <asm/uaccess.h>
39#include "internal.h"
40
41#define RAMFS_DEFAULT_MODE	0755
42
43static const struct super_operations ramfs_ops;
44static const struct inode_operations ramfs_dir_inode_operations;
45
46static const struct address_space_operations ramfs_aops = {
47	.readpage	= simple_readpage,
48	.write_begin	= simple_write_begin,
49	.write_end	= simple_write_end,
50	.set_page_dirty	= __set_page_dirty_no_writeback,
51};
52
53struct inode *ramfs_get_inode(struct super_block *sb,
54				const struct inode *dir, umode_t mode, dev_t dev)
55{
56	struct inode * inode = new_inode(sb);
57
58	if (inode) {
59		inode->i_ino = get_next_ino();
60		inode_init_owner(inode, dir, mode);
61		inode->i_mapping->a_ops = &ramfs_aops;
62		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
63		mapping_set_unevictable(inode->i_mapping);
64		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
65		switch (mode & S_IFMT) {
66		default:
67			init_special_inode(inode, mode, dev);
68			break;
69		case S_IFREG:
70			inode->i_op = &ramfs_file_inode_operations;
71			inode->i_fop = &ramfs_file_operations;
72			break;
73		case S_IFDIR:
74			inode->i_op = &ramfs_dir_inode_operations;
75			inode->i_fop = &simple_dir_operations;
76
77			/* directory inodes start off with i_nlink == 2 (for "." entry) */
78			inc_nlink(inode);
79			break;
80		case S_IFLNK:
81			inode->i_op = &page_symlink_inode_operations;
82			break;
83		}
84	}
85	return inode;
86}
87
88/*
89 * File creation. Allocate an inode, and we're done..
90 */
91/* SMP-safe */
92static int
93ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
94{
95	struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
96	int error = -ENOSPC;
97
98	if (inode) {
99		d_instantiate(dentry, inode);
100		dget(dentry);	/* Extra count - pin the dentry in core */
101		error = 0;
102		dir->i_mtime = dir->i_ctime = CURRENT_TIME;
103	}
104	return error;
105}
106
107static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
108{
109	int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
110	if (!retval)
111		inc_nlink(dir);
112	return retval;
113}
114
115static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
116{
117	return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
118}
119
120static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
121{
122	struct inode *inode;
123	int error = -ENOSPC;
124
125	inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
126	if (inode) {
127		int l = strlen(symname)+1;
128		error = page_symlink(inode, symname, l);
129		if (!error) {
130			d_instantiate(dentry, inode);
131			dget(dentry);
132			dir->i_mtime = dir->i_ctime = CURRENT_TIME;
133		} else
134			iput(inode);
135	}
136	return error;
137}
138
139static const struct inode_operations ramfs_dir_inode_operations = {
140	.create		= ramfs_create,
141	.lookup		= simple_lookup,
142	.link		= simple_link,
143	.unlink		= simple_unlink,
144	.symlink	= ramfs_symlink,
145	.mkdir		= ramfs_mkdir,
146	.rmdir		= simple_rmdir,
147	.mknod		= ramfs_mknod,
148	.rename		= simple_rename,
149};
150
151static const struct super_operations ramfs_ops = {
152	.statfs		= simple_statfs,
153	.drop_inode	= generic_delete_inode,
154	.show_options	= generic_show_options,
155};
156
157struct ramfs_mount_opts {
158	umode_t mode;
159};
160
161enum {
162	Opt_mode,
163	Opt_err
164};
165
166static const match_table_t tokens = {
167	{Opt_mode, "mode=%o"},
168	{Opt_err, NULL}
169};
170
171struct ramfs_fs_info {
172	struct ramfs_mount_opts mount_opts;
173};
174
175static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
176{
177	substring_t args[MAX_OPT_ARGS];
178	int option;
179	int token;
180	char *p;
181
182	opts->mode = RAMFS_DEFAULT_MODE;
183
184	while ((p = strsep(&data, ",")) != NULL) {
185		if (!*p)
186			continue;
187
188		token = match_token(p, tokens, args);
189		switch (token) {
190		case Opt_mode:
191			if (match_octal(&args[0], &option))
192				return -EINVAL;
193			opts->mode = option & S_IALLUGO;
194			break;
195		/*
196		 * We might like to report bad mount options here;
197		 * but traditionally ramfs has ignored all mount options,
198		 * and as it is used as a !CONFIG_SHMEM simple substitute
199		 * for tmpfs, better continue to ignore other mount options.
200		 */
201		}
202	}
203
204	return 0;
205}
206
207int ramfs_fill_super(struct super_block *sb, void *data, int silent)
208{
209	struct ramfs_fs_info *fsi;
210	struct inode *inode;
211	int err;
212
213	save_mount_options(sb, data);
214
215	fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
216	sb->s_fs_info = fsi;
217	if (!fsi)
218		return -ENOMEM;
219
220	err = ramfs_parse_options(data, &fsi->mount_opts);
221	if (err)
222		return err;
223
224	sb->s_maxbytes		= MAX_LFS_FILESIZE;
225	sb->s_blocksize		= PAGE_CACHE_SIZE;
226	sb->s_blocksize_bits	= PAGE_CACHE_SHIFT;
227	sb->s_magic		= RAMFS_MAGIC;
228	sb->s_op		= &ramfs_ops;
229	sb->s_time_gran		= 1;
230
231	inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
232	sb->s_root = d_make_root(inode);
233	if (!sb->s_root)
234		return -ENOMEM;
235
236	return 0;
237}
238
239struct dentry *ramfs_mount(struct file_system_type *fs_type,
240	int flags, const char *dev_name, void *data)
241{
242	return mount_nodev(fs_type, flags, data, ramfs_fill_super);
243}
244
245static void ramfs_kill_sb(struct super_block *sb)
246{
247	kfree(sb->s_fs_info);
248	kill_litter_super(sb);
249}
250
251static struct file_system_type ramfs_fs_type = {
252	.name		= "ramfs",
253	.mount		= ramfs_mount,
254	.kill_sb	= ramfs_kill_sb,
255	.fs_flags	= FS_USERNS_MOUNT,
256};
257
258int __init init_ramfs_fs(void)
259{
260	static unsigned long once;
261
262	if (test_and_set_bit(0, &once))
263		return 0;
264	return register_filesystem(&ramfs_fs_type);
265}
266fs_initcall(init_ramfs_fs);
267