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/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");