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 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);