fs/ramfs/inode.c

   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);