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/module.h> 27 #include <linux/fs.h> 28 #include <linux/pagemap.h> 29 #include <linux/highmem.h> 30 #include <linux/init.h> 31 #include <linux/string.h> 32 #include <linux/smp_lock.h> 33 #include <linux/backing-dev.h> 34 #include <linux/ramfs.h> 35 36 #include <asm/uaccess.h> 37 38 /* some random number */ 39 #define RAMFS_MAGIC 0x858458f6 40 41 static struct super_operations ramfs_ops; 42 static struct address_space_operations ramfs_aops; 43 static struct inode_operations ramfs_file_inode_operations; 44 static struct inode_operations ramfs_dir_inode_operations; 45 46 static struct backing_dev_info ramfs_backing_dev_info = { 47 .ra_pages = 0, /* No readahead */ 48 .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK | 49 BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY | 50 BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP, 51 }; 52 53 struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev) 54 { 55 struct inode * inode = new_inode(sb); 56 57 if (inode) { 58 inode->i_mode = mode; 59 inode->i_uid = current->fsuid; 60 inode->i_gid = current->fsgid; 61 inode->i_blksize = PAGE_CACHE_SIZE; 62 inode->i_blocks = 0; 63 inode->i_mapping->a_ops = &ramfs_aops; 64 inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info; 65 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; 66 switch (mode & S_IFMT) { 67 default: 68 init_special_inode(inode, mode, dev); 69 break; 70 case S_IFREG: 71 inode->i_op = &ramfs_file_inode_operations; 72 inode->i_fop = &ramfs_file_operations; 73 break; 74 case S_IFDIR: 75 inode->i_op = &ramfs_dir_inode_operations; 76 inode->i_fop = &simple_dir_operations; 77 78 /* directory inodes start off with i_nlink == 2 (for "." entry) */ 79 inode->i_nlink++; 80 break; 81 case S_IFLNK: 82 inode->i_op = &page_symlink_inode_operations; 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, int mode, dev_t dev) 95 { 96 struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev); 97 int error = -ENOSPC; 98 99 if (inode) { 100 if (dir->i_mode & S_ISGID) { 101 inode->i_gid = dir->i_gid; 102 if (S_ISDIR(mode)) 103 inode->i_mode |= S_ISGID; 104 } 105 d_instantiate(dentry, inode); 106 dget(dentry); /* Extra count - pin the dentry in core */ 107 error = 0; 108 } 109 return error; 110 } 111 112 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode) 113 { 114 int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0); 115 if (!retval) 116 dir->i_nlink++; 117 return retval; 118 } 119 120 static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode, struct nameidata *nd) 121 { 122 return ramfs_mknod(dir, dentry, mode | S_IFREG, 0); 123 } 124 125 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname) 126 { 127 struct inode *inode; 128 int error = -ENOSPC; 129 130 inode = ramfs_get_inode(dir->i_sb, S_IFLNK|S_IRWXUGO, 0); 131 if (inode) { 132 int l = strlen(symname)+1; 133 error = page_symlink(inode, symname, l); 134 if (!error) { 135 if (dir->i_mode & S_ISGID) 136 inode->i_gid = dir->i_gid; 137 d_instantiate(dentry, inode); 138 dget(dentry); 139 } else 140 iput(inode); 141 } 142 return error; 143 } 144 145 static struct address_space_operations ramfs_aops = { 146 .readpage = simple_readpage, 147 .prepare_write = simple_prepare_write, 148 .commit_write = simple_commit_write 149 }; 150 151 struct file_operations ramfs_file_operations = { 152 .read = generic_file_read, 153 .write = generic_file_write, 154 .mmap = generic_file_mmap, 155 .fsync = simple_sync_file, 156 .sendfile = generic_file_sendfile, 157 .llseek = generic_file_llseek, 158 }; 159 160 static struct inode_operations ramfs_file_inode_operations = { 161 .getattr = simple_getattr, 162 }; 163 164 static struct inode_operations ramfs_dir_inode_operations = { 165 .create = ramfs_create, 166 .lookup = simple_lookup, 167 .link = simple_link, 168 .unlink = simple_unlink, 169 .symlink = ramfs_symlink, 170 .mkdir = ramfs_mkdir, 171 .rmdir = simple_rmdir, 172 .mknod = ramfs_mknod, 173 .rename = simple_rename, 174 }; 175 176 static struct super_operations ramfs_ops = { 177 .statfs = simple_statfs, 178 .drop_inode = generic_delete_inode, 179 }; 180 181 static int ramfs_fill_super(struct super_block * sb, void * data, int silent) 182 { 183 struct inode * inode; 184 struct dentry * root; 185 186 sb->s_maxbytes = MAX_LFS_FILESIZE; 187 sb->s_blocksize = PAGE_CACHE_SIZE; 188 sb->s_blocksize_bits = PAGE_CACHE_SHIFT; 189 sb->s_magic = RAMFS_MAGIC; 190 sb->s_op = &ramfs_ops; 191 sb->s_time_gran = 1; 192 inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0); 193 if (!inode) 194 return -ENOMEM; 195 196 root = d_alloc_root(inode); 197 if (!root) { 198 iput(inode); 199 return -ENOMEM; 200 } 201 sb->s_root = root; 202 return 0; 203 } 204 205 struct super_block *ramfs_get_sb(struct file_system_type *fs_type, 206 int flags, const char *dev_name, void *data) 207 { 208 return get_sb_nodev(fs_type, flags, data, ramfs_fill_super); 209 } 210 211 static struct super_block *rootfs_get_sb(struct file_system_type *fs_type, 212 int flags, const char *dev_name, void *data) 213 { 214 return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super); 215 } 216 217 static struct file_system_type ramfs_fs_type = { 218 .name = "ramfs", 219 .get_sb = ramfs_get_sb, 220 .kill_sb = kill_litter_super, 221 }; 222 static struct file_system_type rootfs_fs_type = { 223 .name = "rootfs", 224 .get_sb = rootfs_get_sb, 225 .kill_sb = kill_litter_super, 226 }; 227 228 static int __init init_ramfs_fs(void) 229 { 230 return register_filesystem(&ramfs_fs_type); 231 } 232 233 static void __exit exit_ramfs_fs(void) 234 { 235 unregister_filesystem(&ramfs_fs_type); 236 } 237 238 module_init(init_ramfs_fs) 239 module_exit(exit_ramfs_fs) 240 241 int __init init_rootfs(void) 242 { 243 return register_filesystem(&rootfs_fs_type); 244 } 245 246 MODULE_LICENSE("GPL"); 247