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/time.h>
  31 #include <linux/init.h>
  32 #include <linux/string.h>
  33 #include <linux/backing-dev.h>
  34 #include <linux/ramfs.h>
  35 #include <linux/sched.h>
  36 #include <asm/uaccess.h>
  37 #include "internal.h"
  38
  39 /* some random number */
  40 #define RAMFS_MAGIC     0x858458f6
  41
  42 static const struct super_operations ramfs_ops;
  43 static const struct inode_operations ramfs_dir_inode_operations;
  44
  45 static struct backing_dev_info ramfs_backing_dev_info = {
  46         .ra_pages       = 0,    /* No readahead */
  47         .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK |
  48                           BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
  49                           BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
  50 };
  51
  52 struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev)
  53 {
  54         struct inode * inode = new_inode(sb);
  55
  56         if (inode) {
  57                 inode->i_mode = mode;
  58                 inode->i_uid = current->fsuid;
  59                 inode->i_gid = current->fsgid;
  60                 inode->i_blocks = 0;
  61                 inode->i_mapping->a_ops = &ramfs_aops;
  62                 inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
  63                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  64                 switch (mode & S_IFMT) {
  65                 default:
  66                         init_special_inode(inode, mode, dev);
  67                         break;
  68                 case S_IFREG:
  69                         inode->i_op = &ramfs_file_inode_operations;
  70                         inode->i_fop = &ramfs_file_operations;
  71                         break;
  72                 case S_IFDIR:
  73                         inode->i_op = &ramfs_dir_inode_operations;
  74                         inode->i_fop = &simple_dir_operations;
  75
  76                         /* directory inodes start off with i_nlink == 2 (for "." entry) */
  77                         inc_nlink(inode);
  78                         break;
  79                 case S_IFLNK:
  80                         inode->i_op = &page_symlink_inode_operations;
  81                         break;
  82                 }
  83         }
  84         return inode;
  85 }
  86
  87 /*
  88  * File creation. Allocate an inode, and we're done..
  89  */
  90 /* SMP-safe */
  91 static int
  92 ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
  93 {
  94         struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
  95         int error = -ENOSPC;
  96
  97         if (inode) {
  98                 if (dir->i_mode & S_ISGID) {
  99                         inode->i_gid = dir->i_gid;
 100                         if (S_ISDIR(mode))
 101                                 inode->i_mode |= S_ISGID;
 102                 }
 103                 d_instantiate(dentry, inode);
 104                 dget(dentry);   /* Extra count - pin the dentry in core */
 105                 error = 0;
 106                 dir->i_mtime = dir->i_ctime = CURRENT_TIME;
 107         }
 108         return error;
 109 }
 110
 111 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
 112 {
 113         int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
 114         if (!retval)
 115                 inc_nlink(dir);
 116         return retval;
 117 }
 118
 119 static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode, struct nameidata *nd)
 120 {
 121         return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
 122 }
 123
 124 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
 125 {
 126         struct inode *inode;
 127         int error = -ENOSPC;
 128
 129         inode = ramfs_get_inode(dir->i_sb, S_IFLNK|S_IRWXUGO, 0);
 130         if (inode) {
 131                 int l = strlen(symname)+1;
 132                 error = page_symlink(inode, symname, l);
 133                 if (!error) {
 134                         if (dir->i_mode & S_ISGID)
 135                                 inode->i_gid = dir->i_gid;
 136                         d_instantiate(dentry, inode);
 137                         dget(dentry);
 138                         dir->i_mtime = dir->i_ctime = CURRENT_TIME;
 139                 } else
 140                         iput(inode);
 141         }
 142         return error;
 143 }
 144
 145 static const struct inode_operations ramfs_dir_inode_operations = {
 146         .create         = ramfs_create,
 147         .lookup         = simple_lookup,
 148         .link           = simple_link,
 149         .unlink         = simple_unlink,
 150         .symlink        = ramfs_symlink,
 151         .mkdir          = ramfs_mkdir,
 152         .rmdir          = simple_rmdir,
 153         .mknod          = ramfs_mknod,
 154         .rename         = simple_rename,
 155 };
 156
 157 static const struct super_operations ramfs_ops = {
 158         .statfs         = simple_statfs,
 159         .drop_inode     = generic_delete_inode,
 160 };
 161
 162 static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
 163 {
 164         struct inode * inode;
 165         struct dentry * root;
 166
 167         sb->s_maxbytes = MAX_LFS_FILESIZE;
 168         sb->s_blocksize = PAGE_CACHE_SIZE;
 169         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 170         sb->s_magic = RAMFS_MAGIC;
 171         sb->s_op = &ramfs_ops;
 172         sb->s_time_gran = 1;
 173         inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
 174         if (!inode)
 175                 return -ENOMEM;
 176
 177         root = d_alloc_root(inode);
 178         if (!root) {
 179                 iput(inode);
 180                 return -ENOMEM;
 181         }
 182         sb->s_root = root;
 183         return 0;
 184 }
 185
 186 int ramfs_get_sb(struct file_system_type *fs_type,
 187         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 188 {
 189         return get_sb_nodev(fs_type, flags, data, ramfs_fill_super, mnt);
 190 }
 191
 192 static int rootfs_get_sb(struct file_system_type *fs_type,
 193         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 194 {
 195         return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super,
 196                             mnt);
 197 }
 198
 199 static struct file_system_type ramfs_fs_type = {
 200         .name           = "ramfs",
 201         .get_sb         = ramfs_get_sb,
 202         .kill_sb        = kill_litter_super,
 203 };
 204 static struct file_system_type rootfs_fs_type = {
 205         .name           = "rootfs",
 206         .get_sb         = rootfs_get_sb,
 207         .kill_sb        = kill_litter_super,
 208 };
 209
 210 static int __init init_ramfs_fs(void)
 211 {
 212         return register_filesystem(&ramfs_fs_type);
 213 }
 214
 215 static void __exit exit_ramfs_fs(void)
 216 {
 217         unregister_filesystem(&ramfs_fs_type);
 218 }
 219
 220 module_init(init_ramfs_fs)
 221 module_exit(exit_ramfs_fs)
 222
 223 int __init init_rootfs(void)
 224 {
 225         return register_filesystem(&rootfs_fs_type);
 226 }
 227
 228 MODULE_LICENSE("GPL");