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 "internal.h" 42 43 struct ramfs_mount_opts { 44 umode_t mode; 45 }; 46 47 struct ramfs_fs_info { 48 struct ramfs_mount_opts mount_opts; 49 }; 50 51 #define RAMFS_DEFAULT_MODE 0755 52 53 static const struct super_operations ramfs_ops; 54 static const struct inode_operations ramfs_dir_inode_operations; 55 56 static const struct address_space_operations ramfs_aops = { 57 .readpage = simple_readpage, 58 .write_begin = simple_write_begin, 59 .write_end = simple_write_end, 60 .set_page_dirty = __set_page_dirty_no_writeback, 61 }; 62 63 struct inode *ramfs_get_inode(struct super_block *sb, 64 const struct inode *dir, umode_t mode, dev_t dev) 65 { 66 struct inode * inode = new_inode(sb); 67 68 if (inode) { 69 inode->i_ino = get_next_ino(); 70 inode_init_owner(&init_user_ns, inode, dir, mode); 71 inode->i_mapping->a_ops = &ramfs_aops; 72 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); 73 mapping_set_unevictable(inode->i_mapping); 74 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); 75 switch (mode & S_IFMT) { 76 default: 77 init_special_inode(inode, mode, dev); 78 break; 79 case S_IFREG: 80 inode->i_op = &ramfs_file_inode_operations; 81 inode->i_fop = &ramfs_file_operations; 82 break; 83 case S_IFDIR: 84 inode->i_op = &ramfs_dir_inode_operations; 85 inode->i_fop = &simple_dir_operations; 86 87 /* directory inodes start off with i_nlink == 2 (for "." entry) */ 88 inc_nlink(inode); 89 break; 90 case S_IFLNK: 91 inode->i_op = &page_symlink_inode_operations; 92 inode_nohighmem(inode); 93 break; 94 } 95 } 96 return inode; 97 } 98 99 /* 100 * File creation. Allocate an inode, and we're done.. 101 */ 102 /* SMP-safe */ 103 static int 104 ramfs_mknod(struct user_namespace *mnt_userns, struct inode *dir, 105 struct dentry *dentry, umode_t mode, dev_t dev) 106 { 107 struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev); 108 int error = -ENOSPC; 109 110 if (inode) { 111 d_instantiate(dentry, inode); 112 dget(dentry); /* Extra count - pin the dentry in core */ 113 error = 0; 114 dir->i_mtime = dir->i_ctime = current_time(dir); 115 } 116 return error; 117 } 118 119 static int ramfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir, 120 struct dentry *dentry, umode_t mode) 121 { 122 int retval = ramfs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0); 123 if (!retval) 124 inc_nlink(dir); 125 return retval; 126 } 127 128 static int ramfs_create(struct user_namespace *mnt_userns, struct inode *dir, 129 struct dentry *dentry, umode_t mode, bool excl) 130 { 131 return ramfs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0); 132 } 133 134 static int ramfs_symlink(struct user_namespace *mnt_userns, struct inode *dir, 135 struct dentry *dentry, const char *symname) 136 { 137 struct inode *inode; 138 int error = -ENOSPC; 139 140 inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0); 141 if (inode) { 142 int l = strlen(symname)+1; 143 error = page_symlink(inode, symname, l); 144 if (!error) { 145 d_instantiate(dentry, inode); 146 dget(dentry); 147 dir->i_mtime = dir->i_ctime = current_time(dir); 148 } else 149 iput(inode); 150 } 151 return error; 152 } 153 154 static int ramfs_tmpfile(struct user_namespace *mnt_userns, 155 struct inode *dir, struct dentry *dentry, umode_t mode) 156 { 157 struct inode *inode; 158 159 inode = ramfs_get_inode(dir->i_sb, dir, mode, 0); 160 if (!inode) 161 return -ENOSPC; 162 d_tmpfile(dentry, inode); 163 return 0; 164 } 165 166 static const struct inode_operations ramfs_dir_inode_operations = { 167 .create = ramfs_create, 168 .lookup = simple_lookup, 169 .link = simple_link, 170 .unlink = simple_unlink, 171 .symlink = ramfs_symlink, 172 .mkdir = ramfs_mkdir, 173 .rmdir = simple_rmdir, 174 .mknod = ramfs_mknod, 175 .rename = simple_rename, 176 .tmpfile = ramfs_tmpfile, 177 }; 178 179 /* 180 * Display the mount options in /proc/mounts. 181 */ 182 static int ramfs_show_options(struct seq_file *m, struct dentry *root) 183 { 184 struct ramfs_fs_info *fsi = root->d_sb->s_fs_info; 185 186 if (fsi->mount_opts.mode != RAMFS_DEFAULT_MODE) 187 seq_printf(m, ",mode=%o", fsi->mount_opts.mode); 188 return 0; 189 } 190 191 static const struct super_operations ramfs_ops = { 192 .statfs = simple_statfs, 193 .drop_inode = generic_delete_inode, 194 .show_options = ramfs_show_options, 195 }; 196 197 enum ramfs_param { 198 Opt_mode, 199 }; 200 201 const struct fs_parameter_spec ramfs_fs_parameters[] = { 202 fsparam_u32oct("mode", Opt_mode), 203 {} 204 }; 205 206 static int ramfs_parse_param(struct fs_context *fc, struct fs_parameter *param) 207 { 208 struct fs_parse_result result; 209 struct ramfs_fs_info *fsi = fc->s_fs_info; 210 int opt; 211 212 opt = fs_parse(fc, ramfs_fs_parameters, param, &result); 213 if (opt < 0) { 214 /* 215 * We might like to report bad mount options here; 216 * but traditionally ramfs has ignored all mount options, 217 * and as it is used as a !CONFIG_SHMEM simple substitute 218 * for tmpfs, better continue to ignore other mount options. 219 */ 220 if (opt == -ENOPARAM) 221 opt = 0; 222 return opt; 223 } 224 225 switch (opt) { 226 case Opt_mode: 227 fsi->mount_opts.mode = result.uint_32 & S_IALLUGO; 228 break; 229 } 230 231 return 0; 232 } 233 234 static int ramfs_fill_super(struct super_block *sb, struct fs_context *fc) 235 { 236 struct ramfs_fs_info *fsi = sb->s_fs_info; 237 struct inode *inode; 238 239 sb->s_maxbytes = MAX_LFS_FILESIZE; 240 sb->s_blocksize = PAGE_SIZE; 241 sb->s_blocksize_bits = PAGE_SHIFT; 242 sb->s_magic = RAMFS_MAGIC; 243 sb->s_op = &ramfs_ops; 244 sb->s_time_gran = 1; 245 246 inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0); 247 sb->s_root = d_make_root(inode); 248 if (!sb->s_root) 249 return -ENOMEM; 250 251 return 0; 252 } 253 254 static int ramfs_get_tree(struct fs_context *fc) 255 { 256 return get_tree_nodev(fc, ramfs_fill_super); 257 } 258 259 static void ramfs_free_fc(struct fs_context *fc) 260 { 261 kfree(fc->s_fs_info); 262 } 263 264 static const struct fs_context_operations ramfs_context_ops = { 265 .free = ramfs_free_fc, 266 .parse_param = ramfs_parse_param, 267 .get_tree = ramfs_get_tree, 268 }; 269 270 int ramfs_init_fs_context(struct fs_context *fc) 271 { 272 struct ramfs_fs_info *fsi; 273 274 fsi = kzalloc(sizeof(*fsi), GFP_KERNEL); 275 if (!fsi) 276 return -ENOMEM; 277 278 fsi->mount_opts.mode = RAMFS_DEFAULT_MODE; 279 fc->s_fs_info = fsi; 280 fc->ops = &ramfs_context_ops; 281 return 0; 282 } 283 284 static void ramfs_kill_sb(struct super_block *sb) 285 { 286 kfree(sb->s_fs_info); 287 kill_litter_super(sb); 288 } 289 290 static struct file_system_type ramfs_fs_type = { 291 .name = "ramfs", 292 .init_fs_context = ramfs_init_fs_context, 293 .parameters = ramfs_fs_parameters, 294 .kill_sb = ramfs_kill_sb, 295 .fs_flags = FS_USERNS_MOUNT, 296 }; 297 298 static int __init init_ramfs_fs(void) 299 { 300 return register_filesystem(&ramfs_fs_type); 301 } 302 fs_initcall(init_ramfs_fs); 303