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  * This file is released under the GPL.
   8  */
   9
  10 /*
  11  * NOTE! This filesystem is probably most useful
  12  * not as a real filesystem, but as an example of
  13  * how virtual filesystems can be written.
  14  *
  15  * It doesn't get much simpler than this. Consider
  16  * that this file implements the full semantics of
  17  * a POSIX-compliant read-write filesystem.
  18  *
  19  * Note in particular how the filesystem does not
  20  * need to implement any data structures of its own
  21  * to keep track of the virtual data: using the VFS
  22  * caches is sufficient.
  23  */
  24
  25 #include <linux/module.h>
  26 #include <linux/fs.h>
  27 #include <linux/pagemap.h>
  28 #include <linux/init.h>
  29 #include <linux/string.h>
  30 #include <linux/locks.h>
  31
  32 #include <asm/uaccess.h>
  33
  34 /* some random number */
  35 #define RAMFS_MAGIC     0x858458f6
  36
  37 static struct super_operations ramfs_ops;
  38 static struct address_space_operations ramfs_aops;
  39 static struct file_operations ramfs_dir_operations;
  40 static struct file_operations ramfs_file_operations;
  41 static struct inode_operations ramfs_dir_inode_operations;
  42
  43 static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
  44 {
  45         buf->f_type = RAMFS_MAGIC;
  46         buf->f_bsize = PAGE_CACHE_SIZE;
  47         buf->f_namelen = 255;
  48         return 0;
  49 }
  50
  51 /*
  52  * Lookup the data. This is trivial - if the dentry didn't already
  53  * exist, we know it is negative.
  54  */
  55 static struct dentry * ramfs_lookup(struct inode *dir, struct dentry *dentry)
  56 {
  57         d_add(dentry, NULL);
  58         return NULL;
  59 }
  60
  61 /*
  62  * Read a page. Again trivial. If it didn't already exist
  63  * in the page cache, it is zero-filled.
  64  */
  65 static int ramfs_readpage(struct file *file, struct page * page)
  66 {
  67         if (!Page_Uptodate(page)) {
  68                 memset(kmap(page), 0, PAGE_CACHE_SIZE);
  69                 kunmap(page);
  70                 flush_dcache_page(page);
  71                 SetPageUptodate(page);
  72         }
  73         UnlockPage(page);
  74         return 0;
  75 }
  76
  77 /*
  78  * Writing: just make sure the page gets marked dirty, so that
  79  * the page stealer won't grab it.
  80  */
  81 static int ramfs_writepage(struct page *page)
  82 {
  83         SetPageDirty(page);
  84         return 0;
  85 }
  86
  87 static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
  88 {
  89         void *addr = kmap(page);
  90         if (!Page_Uptodate(page)) {
  91                 memset(addr, 0, PAGE_CACHE_SIZE);
  92                 flush_dcache_page(page);
  93                 SetPageUptodate(page);
  94         }
  95         SetPageDirty(page);
  96         return 0;
  97 }
  98
  99 static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
 100 {
 101         struct inode *inode = (struct inode*)page->mapping->host;
 102         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
 103
 104         kunmap(page);
 105         if (pos > inode->i_size)
 106                 inode->i_size = pos;
 107         return 0;
 108 }
 109
 110 struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
 111 {
 112         struct inode * inode = new_inode(sb);
 113
 114         if (inode) {
 115                 inode->i_mode = mode;
 116                 inode->i_uid = current->fsuid;
 117                 inode->i_gid = current->fsgid;
 118                 inode->i_blksize = PAGE_CACHE_SIZE;
 119                 inode->i_blocks = 0;
 120                 inode->i_rdev = to_kdev_t(dev);
 121                 inode->i_mapping->a_ops = &ramfs_aops;
 122                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 123                 switch (mode & S_IFMT) {
 124                 default:
 125                         init_special_inode(inode, mode, dev);
 126                         break;
 127                 case S_IFREG:
 128                         inode->i_fop = &ramfs_file_operations;
 129                         break;
 130                 case S_IFDIR:
 131                         inode->i_op = &ramfs_dir_inode_operations;
 132                         inode->i_fop = &ramfs_dir_operations;
 133                         break;
 134                 case S_IFLNK:
 135                         inode->i_op = &page_symlink_inode_operations;
 136                         break;
 137                 }
 138         }
 139         return inode;
 140 }
 141
 142 /*
 143  * File creation. Allocate an inode, and we're done..
 144  */
 145 static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
 146 {
 147         struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
 148         int error = -ENOSPC;
 149
 150         if (inode) {
 151                 d_instantiate(dentry, inode);
 152                 dget(dentry);           /* Extra count - pin the dentry in core */
 153                 error = 0;
 154         }
 155         return error;
 156 }
 157
 158 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
 159 {
 160         return ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
 161 }
 162
 163 static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode)
 164 {
 165         return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
 166 }
 167
 168 /*
 169  * Link a file..
 170  */
 171 static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
 172 {
 173         struct inode *inode = old_dentry->d_inode;
 174
 175         if (S_ISDIR(inode->i_mode))
 176                 return -EPERM;
 177
 178         inode->i_nlink++;
 179         atomic_inc(&inode->i_count);    /* New dentry reference */
 180         dget(dentry);           /* Extra pinning count for the created dentry */
 181         d_instantiate(dentry, inode);
 182         return 0;
 183 }
 184
 185 static inline int ramfs_positive(struct dentry *dentry)
 186 {
 187         return dentry->d_inode && !d_unhashed(dentry);
 188 }
 189
 190 /*
 191  * Check that a directory is empty (this works
 192  * for regular files too, they'll just always be
 193  * considered empty..).
 194  *
 195  * Note that an empty directory can still have
 196  * children, they just all have to be negative..
 197  */
 198 static int ramfs_empty(struct dentry *dentry)
 199 {
 200         struct list_head *list;
 201
 202         spin_lock(&dcache_lock);
 203         list = dentry->d_subdirs.next;
 204
 205         while (list != &dentry->d_subdirs) {
 206                 struct dentry *de = list_entry(list, struct dentry, d_child);
 207
 208                 if (ramfs_positive(de)) {
 209                         spin_unlock(&dcache_lock);
 210                         return 0;
 211                 }
 212                 list = list->next;
 213         }
 214         spin_unlock(&dcache_lock);
 215         return 1;
 216 }
 217
 218 /*
 219  * This works for both directories and regular files.
 220  * (non-directories will always have empty subdirs)
 221  */
 222 static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
 223 {
 224         int retval = -ENOTEMPTY;
 225
 226         if (ramfs_empty(dentry)) {
 227                 struct inode *inode = dentry->d_inode;
 228
 229                 inode->i_nlink--;
 230                 dput(dentry);                   /* Undo the count from "create" - this does all the work */
 231                 retval = 0;
 232         }
 233         return retval;
 234 }
 235
 236 #define ramfs_rmdir ramfs_unlink
 237
 238 /*
 239  * The VFS layer already does all the dentry stuff for rename,
 240  * we just have to decrement the usage count for the target if
 241  * it exists so that the VFS layer correctly free's it when it
 242  * gets overwritten.
 243  */
 244 static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
 245 {
 246         int error = -ENOTEMPTY;
 247
 248         if (ramfs_empty(new_dentry)) {
 249                 struct inode *inode = new_dentry->d_inode;
 250                 if (inode) {
 251                         inode->i_nlink--;
 252                         dput(new_dentry);
 253                 }
 254                 error = 0;
 255         }
 256         return error;
 257 }
 258
 259 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
 260 {
 261         int error;
 262
 263         error = ramfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
 264         if (!error) {
 265                 int l = strlen(symname)+1;
 266                 struct inode *inode = dentry->d_inode;
 267                 error = block_symlink(inode, symname, l);
 268         }
 269         return error;
 270 }
 271
 272 static struct address_space_operations ramfs_aops = {
 273         readpage:       ramfs_readpage,
 274         writepage:      ramfs_writepage,
 275         prepare_write:  ramfs_prepare_write,
 276         commit_write:   ramfs_commit_write
 277 };
 278
 279 static struct file_operations ramfs_file_operations = {
 280         read:           generic_file_read,
 281         write:          generic_file_write,
 282         mmap:           generic_file_mmap
 283 };
 284
 285 static struct file_operations ramfs_dir_operations = {
 286         read:           generic_read_dir,
 287         readdir:        dcache_readdir,
 288 };
 289
 290 static struct inode_operations ramfs_dir_inode_operations = {
 291         create:         ramfs_create,
 292         lookup:         ramfs_lookup,
 293         link:           ramfs_link,
 294         unlink:         ramfs_unlink,
 295         symlink:        ramfs_symlink,
 296         mkdir:          ramfs_mkdir,
 297         rmdir:          ramfs_rmdir,
 298         mknod:          ramfs_mknod,
 299         rename:         ramfs_rename,
 300 };
 301
 302 static struct super_operations ramfs_ops = {
 303         statfs:         ramfs_statfs,
 304         put_inode:      force_delete,
 305 };
 306
 307 static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
 308 {
 309         struct inode * inode;
 310         struct dentry * root;
 311
 312         sb->s_blocksize = PAGE_CACHE_SIZE;
 313         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
 314         sb->s_magic = RAMFS_MAGIC;
 315         sb->s_op = &ramfs_ops;
 316         inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
 317         if (!inode)
 318                 return NULL;
 319
 320         root = d_alloc_root(inode);
 321         if (!root) {
 322                 iput(inode);
 323                 return NULL;
 324         }
 325         sb->s_root = root;
 326         return sb;
 327 }
 328
 329 static DECLARE_FSTYPE(ramfs_fs_type, "ramfs", ramfs_read_super, FS_LITTER);
 330
 331 static int __init init_ramfs_fs(void)
 332 {
 333         return register_filesystem(&ramfs_fs_type);
 334 }
 335
 336 static void __exit exit_ramfs_fs(void)
 337 {
 338         unregister_filesystem(&ramfs_fs_type);
 339 }
 340
 341 module_init(init_ramfs_fs)
 342 module_exit(exit_ramfs_fs)