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 "internal.h" 40 41 struct ramfs_mount_opts { 42 umode_t mode; 43 }; 44 45 struct ramfs_fs_info { 46 struct ramfs_mount_opts mount_opts; 47 }; 48 49 #define RAMFS_DEFAULT_MODE 0755 50 51 static const struct super_operations ramfs_ops; 52 static const struct inode_operations ramfs_dir_inode_operations; 53 54 static const struct address_space_operations ramfs_aops = { 55 .readpage = simple_readpage, 56 .write_begin = simple_write_begin, 57 .write_end = simple_write_end, 58 .set_page_dirty = __set_page_dirty_no_writeback, 59 }; 60 61 struct inode *ramfs_get_inode(struct super_block *sb, 62 const struct inode *dir, umode_t mode, dev_t dev) 63 { 64 struct inode * inode = new_inode(sb); 65 66 if (inode) { 67 inode->i_ino = get_next_ino(); 68 inode_init_owner(inode, dir, mode); 69 inode->i_mapping->a_ops = &ramfs_aops; 70 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); 71 mapping_set_unevictable(inode->i_mapping); 72 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); 73 switch (mode & S_IFMT) { 74 default: 75 init_special_inode(inode, mode, dev); 76 break; 77 case S_IFREG: 78 inode->i_op = &ramfs_file_inode_operations; 79 inode->i_fop = &ramfs_file_operations; 80 break; 81 case S_IFDIR: 82 inode->i_op = &ramfs_dir_inode_operations; 83 inode->i_fop = &simple_dir_operations; 84 85 /* directory inodes start off with i_nlink == 2 (for "." entry) */ 86 inc_nlink(inode); 87 break; 88 case S_IFLNK: 89 inode->i_op = &page_symlink_inode_operations; 90 inode_nohighmem(inode); 91 break; 92 } 93 } 94 return inode; 95 } 96 97 /* 98 * File creation. Allocate an inode, and we're done.. 99 */ 100 /* SMP-safe */ 101 static int 102 ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev) 103 { 104 struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev); 105 int error = -ENOSPC; 106 107 if (inode) { 108 d_instantiate(dentry, inode); 109 dget(dentry); /* Extra count - pin the dentry in core */ 110 error = 0; 111 dir->i_mtime = dir->i_ctime = current_time(dir); 112 } 113 return error; 114 } 115 116 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode) 117 { 118 int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0); 119 if (!retval) 120 inc_nlink(dir); 121 return retval; 122 } 123 124 static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl) 125 { 126 return ramfs_mknod(dir, dentry, mode | S_IFREG, 0); 127 } 128 129 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname) 130 { 131 struct inode *inode; 132 int error = -ENOSPC; 133 134 inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0); 135 if (inode) { 136 int l = strlen(symname)+1; 137 error = page_symlink(inode, symname, l); 138 if (!error) { 139 d_instantiate(dentry, inode); 140 dget(dentry); 141 dir->i_mtime = dir->i_ctime = current_time(dir); 142 } else 143 iput(inode); 144 } 145 return error; 146 } 147 148 static const struct inode_operations ramfs_dir_inode_operations = { 149 .create = ramfs_create, 150 .lookup = simple_lookup, 151 .link = simple_link, 152 .unlink = simple_unlink, 153 .symlink = ramfs_symlink, 154 .mkdir = ramfs_mkdir, 155 .rmdir = simple_rmdir, 156 .mknod = ramfs_mknod, 157 .rename = simple_rename, 158 }; 159 160 /* 161 * Display the mount options in /proc/mounts. 162 */ 163 static int ramfs_show_options(struct seq_file *m, struct dentry *root) 164 { 165 struct ramfs_fs_info *fsi = root->d_sb->s_fs_info; 166 167 if (fsi->mount_opts.mode != RAMFS_DEFAULT_MODE) 168 seq_printf(m, ",mode=%o", fsi->mount_opts.mode); 169 return 0; 170 } 171 172 static const struct super_operations ramfs_ops = { 173 .statfs = simple_statfs, 174 .drop_inode = generic_delete_inode, 175 .show_options = ramfs_show_options, 176 }; 177 178 enum { 179 Opt_mode, 180 Opt_err 181 }; 182 183 static const match_table_t tokens = { 184 {Opt_mode, "mode=%o"}, 185 {Opt_err, NULL} 186 }; 187 188 static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts) 189 { 190 substring_t args[MAX_OPT_ARGS]; 191 int option; 192 int token; 193 char *p; 194 195 opts->mode = RAMFS_DEFAULT_MODE; 196 197 while ((p = strsep(&data, ",")) != NULL) { 198 if (!*p) 199 continue; 200 201 token = match_token(p, tokens, args); 202 switch (token) { 203 case Opt_mode: 204 if (match_octal(&args[0], &option)) 205 return -EINVAL; 206 opts->mode = option & S_IALLUGO; 207 break; 208 /* 209 * We might like to report bad mount options here; 210 * but traditionally ramfs has ignored all mount options, 211 * and as it is used as a !CONFIG_SHMEM simple substitute 212 * for tmpfs, better continue to ignore other mount options. 213 */ 214 } 215 } 216 217 return 0; 218 } 219 220 int ramfs_fill_super(struct super_block *sb, void *data, int silent) 221 { 222 struct ramfs_fs_info *fsi; 223 struct inode *inode; 224 int err; 225 226 fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL); 227 sb->s_fs_info = fsi; 228 if (!fsi) 229 return -ENOMEM; 230 231 err = ramfs_parse_options(data, &fsi->mount_opts); 232 if (err) 233 return err; 234 235 sb->s_maxbytes = MAX_LFS_FILESIZE; 236 sb->s_blocksize = PAGE_SIZE; 237 sb->s_blocksize_bits = PAGE_SHIFT; 238 sb->s_magic = RAMFS_MAGIC; 239 sb->s_op = &ramfs_ops; 240 sb->s_time_gran = 1; 241 242 inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0); 243 sb->s_root = d_make_root(inode); 244 if (!sb->s_root) 245 return -ENOMEM; 246 247 return 0; 248 } 249 250 struct dentry *ramfs_mount(struct file_system_type *fs_type, 251 int flags, const char *dev_name, void *data) 252 { 253 return mount_nodev(fs_type, flags, data, ramfs_fill_super); 254 } 255 256 static void ramfs_kill_sb(struct super_block *sb) 257 { 258 kfree(sb->s_fs_info); 259 kill_litter_super(sb); 260 } 261 262 static struct file_system_type ramfs_fs_type = { 263 .name = "ramfs", 264 .mount = ramfs_mount, 265 .kill_sb = ramfs_kill_sb, 266 .fs_flags = FS_USERNS_MOUNT, 267 }; 268 269 int __init init_ramfs_fs(void) 270 { 271 static unsigned long once; 272 273 if (test_and_set_bit(0, &once)) 274 return 0; 275 return register_filesystem(&ramfs_fs_type); 276 } 277 fs_initcall(init_ramfs_fs); 278