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