fs/libfs.c

   1 /*
   2  *      fs/libfs.c
   3  *      Library for filesystems writers.
   4  */
   5
   6 #include <linux/module.h>
   7 #include <linux/pagemap.h>
   8 #include <linux/mount.h>
   9 #include <linux/vfs.h>
  10 #include <asm/uaccess.h>
  11
  12 int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
  13                    struct kstat *stat)
  14 {
  15         struct inode *inode = dentry->d_inode;
  16         generic_fillattr(inode, stat);
  17         stat->blocks = inode->i_mapping->nrpages << (PAGE_CACHE_SHIFT - 9);
  18         return 0;
  19 }
  20
  21 int simple_statfs(struct super_block *sb, struct kstatfs *buf)
  22 {
  23         buf->f_type = sb->s_magic;
  24         buf->f_bsize = PAGE_CACHE_SIZE;
  25         buf->f_namelen = NAME_MAX;
  26         return 0;
  27 }
  28
  29 /*
  30  * Retaining negative dentries for an in-memory filesystem just wastes
  31  * memory and lookup time: arrange for them to be deleted immediately.
  32  */
  33 static int simple_delete_dentry(struct dentry *dentry)
  34 {
  35         return 1;
  36 }
  37
  38 /*
  39  * Lookup the data. This is trivial - if the dentry didn't already
  40  * exist, we know it is negative.  Set d_op to delete negative dentries.
  41  */
  42 struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
  43 {
  44         static struct dentry_operations simple_dentry_operations = {
  45                 .d_delete = simple_delete_dentry,
  46         };
  47
  48         if (dentry->d_name.len > NAME_MAX)
  49                 return ERR_PTR(-ENAMETOOLONG);
  50         dentry->d_op = &simple_dentry_operations;
  51         d_add(dentry, NULL);
  52         return NULL;
  53 }
  54
  55 int simple_sync_file(struct file * file, struct dentry *dentry, int datasync)
  56 {
  57         return 0;
  58 }
  59
  60 int dcache_dir_open(struct inode *inode, struct file *file)
  61 {
  62         static struct qstr cursor_name = {.len = 1, .name = "."};
  63
  64         file->private_data = d_alloc(file->f_dentry, &cursor_name);
  65
  66         return file->private_data ? 0 : -ENOMEM;
  67 }
  68
  69 int dcache_dir_close(struct inode *inode, struct file *file)
  70 {
  71         dput(file->private_data);
  72         return 0;
  73 }
  74
  75 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin)
  76 {
  77         down(&file->f_dentry->d_inode->i_sem);
  78         switch (origin) {
  79                 case 1:
  80                         offset += file->f_pos;
  81                 case 0:
  82                         if (offset >= 0)
  83                                 break;
  84                 default:
  85                         up(&file->f_dentry->d_inode->i_sem);
  86                         return -EINVAL;
  87         }
  88         if (offset != file->f_pos) {
  89                 file->f_pos = offset;
  90                 if (file->f_pos >= 2) {
  91                         struct list_head *p;
  92                         struct dentry *cursor = file->private_data;
  93                         loff_t n = file->f_pos - 2;
  94
  95                         spin_lock(&dcache_lock);
  96                         list_del(&cursor->d_child);
  97                         p = file->f_dentry->d_subdirs.next;
  98                         while (n && p != &file->f_dentry->d_subdirs) {
  99                                 struct dentry *next;
 100                                 next = list_entry(p, struct dentry, d_child);
 101                                 if (!d_unhashed(next) && next->d_inode)
 102                                         n--;
 103                                 p = p->next;
 104                         }
 105                         list_add_tail(&cursor->d_child, p);
 106                         spin_unlock(&dcache_lock);
 107                 }
 108         }
 109         up(&file->f_dentry->d_inode->i_sem);
 110         return offset;
 111 }
 112
 113 /* Relationship between i_mode and the DT_xxx types */
 114 static inline unsigned char dt_type(struct inode *inode)
 115 {
 116         return (inode->i_mode >> 12) & 15;
 117 }
 118
 119 /*
 120  * Directory is locked and all positive dentries in it are safe, since
 121  * for ramfs-type trees they can't go away without unlink() or rmdir(),
 122  * both impossible due to the lock on directory.
 123  */
 124
 125 int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
 126 {
 127         struct dentry *dentry = filp->f_dentry;
 128         struct dentry *cursor = filp->private_data;
 129         struct list_head *p, *q = &cursor->d_child;
 130         ino_t ino;
 131         int i = filp->f_pos;
 132
 133         switch (i) {
 134                 case 0:
 135                         ino = dentry->d_inode->i_ino;
 136                         if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
 137                                 break;
 138                         filp->f_pos++;
 139                         i++;
 140                         /* fallthrough */
 141                 case 1:
 142                         ino = parent_ino(dentry);
 143                         if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
 144                                 break;
 145                         filp->f_pos++;
 146                         i++;
 147                         /* fallthrough */
 148                 default:
 149                         spin_lock(&dcache_lock);
 150                         if (filp->f_pos == 2) {
 151                                 list_del(q);
 152                                 list_add(q, &dentry->d_subdirs);
 153                         }
 154                         for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
 155                                 struct dentry *next;
 156                                 next = list_entry(p, struct dentry, d_child);
 157                                 if (d_unhashed(next) || !next->d_inode)
 158                                         continue;
 159
 160                                 spin_unlock(&dcache_lock);
 161                                 if (filldir(dirent, next->d_name.name, next->d_name.len, filp->f_pos, next->d_inode->i_ino, dt_type(next->d_inode)) < 0)
 162                                         return 0;
 163                                 spin_lock(&dcache_lock);
 164                                 /* next is still alive */
 165                                 list_del(q);
 166                                 list_add(q, p);
 167                                 p = q;
 168                                 filp->f_pos++;
 169                         }
 170                         spin_unlock(&dcache_lock);
 171         }
 172         return 0;
 173 }
 174
 175 ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
 176 {
 177         return -EISDIR;
 178 }
 179
 180 struct file_operations simple_dir_operations = {
 181         .open           = dcache_dir_open,
 182         .release        = dcache_dir_close,
 183         .llseek         = dcache_dir_lseek,
 184         .read           = generic_read_dir,
 185         .readdir        = dcache_readdir,
 186         .fsync          = simple_sync_file,
 187 };
 188
 189 struct inode_operations simple_dir_inode_operations = {
 190         .lookup         = simple_lookup,
 191 };
 192
 193 /*
 194  * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
 195  * will never be mountable)
 196  */
 197 struct super_block *
 198 get_sb_pseudo(struct file_system_type *fs_type, char *name,
 199         struct super_operations *ops, unsigned long magic)
 200 {
 201         struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
 202         static struct super_operations default_ops = {.statfs = simple_statfs};
 203         struct dentry *dentry;
 204         struct inode *root;
 205         struct qstr d_name = {.name = name, .len = strlen(name)};
 206
 207         if (IS_ERR(s))
 208                 return s;
 209
 210         s->s_flags = MS_NOUSER;
 211         s->s_maxbytes = ~0ULL;
 212         s->s_blocksize = 1024;
 213         s->s_blocksize_bits = 10;
 214         s->s_magic = magic;
 215         s->s_op = ops ? ops : &default_ops;
 216         s->s_time_gran = 1;
 217         root = new_inode(s);
 218         if (!root)
 219                 goto Enomem;
 220         root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
 221         root->i_uid = root->i_gid = 0;
 222         root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
 223         dentry = d_alloc(NULL, &d_name);
 224         if (!dentry) {
 225                 iput(root);
 226                 goto Enomem;
 227         }
 228         dentry->d_sb = s;
 229         dentry->d_parent = dentry;
 230         d_instantiate(dentry, root);
 231         s->s_root = dentry;
 232         s->s_flags |= MS_ACTIVE;
 233         return s;
 234
 235 Enomem:
 236         up_write(&s->s_umount);
 237         deactivate_super(s);
 238         return ERR_PTR(-ENOMEM);
 239 }
 240
 241 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 242 {
 243         struct inode *inode = old_dentry->d_inode;
 244
 245         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
 246         inode->i_nlink++;
 247         atomic_inc(&inode->i_count);
 248         dget(dentry);
 249         d_instantiate(dentry, inode);
 250         return 0;
 251 }
 252
 253 static inline int simple_positive(struct dentry *dentry)
 254 {
 255         return dentry->d_inode && !d_unhashed(dentry);
 256 }
 257
 258 int simple_empty(struct dentry *dentry)
 259 {
 260         struct dentry *child;
 261         int ret = 0;
 262
 263         spin_lock(&dcache_lock);
 264         list_for_each_entry(child, &dentry->d_subdirs, d_child)
 265                 if (simple_positive(child))
 266                         goto out;
 267         ret = 1;
 268 out:
 269         spin_unlock(&dcache_lock);
 270         return ret;
 271 }
 272
 273 int simple_unlink(struct inode *dir, struct dentry *dentry)
 274 {
 275         struct inode *inode = dentry->d_inode;
 276
 277         inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
 278         inode->i_nlink--;
 279         dput(dentry);
 280         return 0;
 281 }
 282
 283 int simple_rmdir(struct inode *dir, struct dentry *dentry)
 284 {
 285         if (!simple_empty(dentry))
 286                 return -ENOTEMPTY;
 287
 288         dentry->d_inode->i_nlink--;
 289         simple_unlink(dir, dentry);
 290         dir->i_nlink--;
 291         return 0;
 292 }
 293
 294 int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
 295                 struct inode *new_dir, struct dentry *new_dentry)
 296 {
 297         struct inode *inode = old_dentry->d_inode;
 298         int they_are_dirs = S_ISDIR(old_dentry->d_inode->i_mode);
 299
 300         if (!simple_empty(new_dentry))
 301                 return -ENOTEMPTY;
 302
 303         if (new_dentry->d_inode) {
 304                 simple_unlink(new_dir, new_dentry);
 305                 if (they_are_dirs)
 306                         old_dir->i_nlink--;
 307         } else if (they_are_dirs) {
 308                 old_dir->i_nlink--;
 309                 new_dir->i_nlink++;
 310         }
 311
 312         old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
 313                 new_dir->i_mtime = inode->i_ctime = CURRENT_TIME;
 314
 315         return 0;
 316 }
 317
 318 int simple_readpage(struct file *file, struct page *page)
 319 {
 320         void *kaddr;
 321
 322         if (PageUptodate(page))
 323                 goto out;
 324
 325         kaddr = kmap_atomic(page, KM_USER0);
 326         memset(kaddr, 0, PAGE_CACHE_SIZE);
 327         kunmap_atomic(kaddr, KM_USER0);
 328         flush_dcache_page(page);
 329         SetPageUptodate(page);
 330 out:
 331         unlock_page(page);
 332         return 0;
 333 }
 334
 335 int simple_prepare_write(struct file *file, struct page *page,
 336                         unsigned from, unsigned to)
 337 {
 338         if (!PageUptodate(page)) {
 339                 if (to - from != PAGE_CACHE_SIZE) {
 340                         void *kaddr = kmap_atomic(page, KM_USER0);
 341                         memset(kaddr, 0, from);
 342                         memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
 343                         flush_dcache_page(page);
 344                         kunmap_atomic(kaddr, KM_USER0);
 345                 }
 346                 SetPageUptodate(page);
 347         }
 348         return 0;
 349 }
 350
 351 int simple_commit_write(struct file *file, struct page *page,
 352                         unsigned offset, unsigned to)
 353 {
 354         struct inode *inode = page->mapping->host;
 355         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
 356
 357         /*
 358          * No need to use i_size_read() here, the i_size
 359          * cannot change under us because we hold the i_sem.
 360          */
 361         if (pos > inode->i_size)
 362                 i_size_write(inode, pos);
 363         set_page_dirty(page);
 364         return 0;
 365 }
 366
 367 int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
 368 {
 369         static struct super_operations s_ops = {.statfs = simple_statfs};
 370         struct inode *inode;
 371         struct dentry *root;
 372         struct dentry *dentry;
 373         int i;
 374
 375         s->s_blocksize = PAGE_CACHE_SIZE;
 376         s->s_blocksize_bits = PAGE_CACHE_SHIFT;
 377         s->s_magic = magic;
 378         s->s_op = &s_ops;
 379         s->s_time_gran = 1;
 380
 381         inode = new_inode(s);
 382         if (!inode)
 383                 return -ENOMEM;
 384         inode->i_mode = S_IFDIR | 0755;
 385         inode->i_uid = inode->i_gid = 0;
 386         inode->i_blksize = PAGE_CACHE_SIZE;
 387         inode->i_blocks = 0;
 388         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 389         inode->i_op = &simple_dir_inode_operations;
 390         inode->i_fop = &simple_dir_operations;
 391         root = d_alloc_root(inode);
 392         if (!root) {
 393                 iput(inode);
 394                 return -ENOMEM;
 395         }
 396         for (i = 0; !files->name || files->name[0]; i++, files++) {
 397                 if (!files->name)
 398                         continue;
 399                 dentry = d_alloc_name(root, files->name);
 400                 if (!dentry)
 401                         goto out;
 402                 inode = new_inode(s);
 403                 if (!inode)
 404                         goto out;
 405                 inode->i_mode = S_IFREG | files->mode;
 406                 inode->i_uid = inode->i_gid = 0;
 407                 inode->i_blksize = PAGE_CACHE_SIZE;
 408                 inode->i_blocks = 0;
 409                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 410                 inode->i_fop = files->ops;
 411                 inode->i_ino = i;
 412                 d_add(dentry, inode);
 413         }
 414         s->s_root = root;
 415         return 0;
 416 out:
 417         d_genocide(root);
 418         dput(root);
 419         return -ENOMEM;
 420 }
 421
 422 static DEFINE_SPINLOCK(pin_fs_lock);
 423
 424 int simple_pin_fs(char *name, struct vfsmount **mount, int *count)
 425 {
 426         struct vfsmount *mnt = NULL;
 427         spin_lock(&pin_fs_lock);
 428         if (unlikely(!*mount)) {
 429                 spin_unlock(&pin_fs_lock);
 430                 mnt = do_kern_mount(name, 0, name, NULL);
 431                 if (IS_ERR(mnt))
 432                         return PTR_ERR(mnt);
 433                 spin_lock(&pin_fs_lock);
 434                 if (!*mount)
 435                         *mount = mnt;
 436         }
 437         mntget(*mount);
 438         ++*count;
 439         spin_unlock(&pin_fs_lock);
 440         mntput(mnt);
 441         return 0;
 442 }
 443
 444 void simple_release_fs(struct vfsmount **mount, int *count)
 445 {
 446         struct vfsmount *mnt;
 447         spin_lock(&pin_fs_lock);
 448         mnt = *mount;
 449         if (!--*count)
 450                 *mount = NULL;
 451         spin_unlock(&pin_fs_lock);
 452         mntput(mnt);
 453 }
 454
 455 ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
 456                                 const void *from, size_t available)
 457 {
 458         loff_t pos = *ppos;
 459         if (pos < 0)
 460                 return -EINVAL;
 461         if (pos >= available)
 462                 return 0;
 463         if (count > available - pos)
 464                 count = available - pos;
 465         if (copy_to_user(to, from + pos, count))
 466                 return -EFAULT;
 467         *ppos = pos + count;
 468         return count;
 469 }
 470
 471 /*
 472  * Transaction based IO.
 473  * The file expects a single write which triggers the transaction, and then
 474  * possibly a read which collects the result - which is stored in a
 475  * file-local buffer.
 476  */
 477 char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
 478 {
 479         struct simple_transaction_argresp *ar;
 480         static DEFINE_SPINLOCK(simple_transaction_lock);
 481
 482         if (size > SIMPLE_TRANSACTION_LIMIT - 1)
 483                 return ERR_PTR(-EFBIG);
 484
 485         ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
 486         if (!ar)
 487                 return ERR_PTR(-ENOMEM);
 488
 489         spin_lock(&simple_transaction_lock);
 490
 491         /* only one write allowed per open */
 492         if (file->private_data) {
 493                 spin_unlock(&simple_transaction_lock);
 494                 free_page((unsigned long)ar);
 495                 return ERR_PTR(-EBUSY);
 496         }
 497
 498         file->private_data = ar;
 499
 500         spin_unlock(&simple_transaction_lock);
 501
 502         if (copy_from_user(ar->data, buf, size))
 503                 return ERR_PTR(-EFAULT);
 504
 505         return ar->data;
 506 }
 507
 508 ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
 509 {
 510         struct simple_transaction_argresp *ar = file->private_data;
 511
 512         if (!ar)
 513                 return 0;
 514         return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
 515 }
 516
 517 int simple_transaction_release(struct inode *inode, struct file *file)
 518 {
 519         free_page((unsigned long)file->private_data);
 520         return 0;
 521 }
 522
 523 /* Simple attribute files */
 524
 525 struct simple_attr {
 526         u64 (*get)(void *);
 527         void (*set)(void *, u64);
 528         char get_buf[24];       /* enough to store a u64 and "\n\0" */
 529         char set_buf[24];
 530         void *data;
 531         const char *fmt;        /* format for read operation */
 532         struct semaphore sem;   /* protects access to these buffers */
 533 };
 534
 535 /* simple_attr_open is called by an actual attribute open file operation
 536  * to set the attribute specific access operations. */
 537 int simple_attr_open(struct inode *inode, struct file *file,
 538                      u64 (*get)(void *), void (*set)(void *, u64),
 539                      const char *fmt)
 540 {
 541         struct simple_attr *attr;
 542
 543         attr = kmalloc(sizeof(*attr), GFP_KERNEL);
 544         if (!attr)
 545                 return -ENOMEM;
 546
 547         attr->get = get;
 548         attr->set = set;
 549         attr->data = inode->u.generic_ip;
 550         attr->fmt = fmt;
 551         init_MUTEX(&attr->sem);
 552
 553         file->private_data = attr;
 554
 555         return nonseekable_open(inode, file);
 556 }
 557
 558 int simple_attr_close(struct inode *inode, struct file *file)
 559 {
 560         kfree(file->private_data);
 561         return 0;
 562 }
 563
 564 /* read from the buffer that is filled with the get function */
 565 ssize_t simple_attr_read(struct file *file, char __user *buf,
 566                          size_t len, loff_t *ppos)
 567 {
 568         struct simple_attr *attr;
 569         size_t size;
 570         ssize_t ret;
 571
 572         attr = file->private_data;
 573
 574         if (!attr->get)
 575                 return -EACCES;
 576
 577         down(&attr->sem);
 578         if (*ppos) /* continued read */
 579                 size = strlen(attr->get_buf);
 580         else      /* first read */
 581                 size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
 582                                  attr->fmt,
 583                                  (unsigned long long)attr->get(attr->data));
 584
 585         ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
 586         up(&attr->sem);
 587         return ret;
 588 }
 589
 590 /* interpret the buffer as a number to call the set function with */
 591 ssize_t simple_attr_write(struct file *file, const char __user *buf,
 592                           size_t len, loff_t *ppos)
 593 {
 594         struct simple_attr *attr;
 595         u64 val;
 596         size_t size;
 597         ssize_t ret;
 598
 599         attr = file->private_data;
 600
 601         if (!attr->set)
 602                 return -EACCES;
 603
 604         down(&attr->sem);
 605         ret = -EFAULT;
 606         size = min(sizeof(attr->set_buf) - 1, len);
 607         if (copy_from_user(attr->set_buf, buf, size))
 608                 goto out;
 609
 610         ret = len; /* claim we got the whole input */
 611         attr->set_buf[size] = '\0';
 612         val = simple_strtol(attr->set_buf, NULL, 0);
 613         attr->set(attr->data, val);
 614 out:
 615         up(&attr->sem);
 616         return ret;
 617 }
 618
 619 EXPORT_SYMBOL(dcache_dir_close);
 620 EXPORT_SYMBOL(dcache_dir_lseek);
 621 EXPORT_SYMBOL(dcache_dir_open);
 622 EXPORT_SYMBOL(dcache_readdir);
 623 EXPORT_SYMBOL(generic_read_dir);
 624 EXPORT_SYMBOL(get_sb_pseudo);
 625 EXPORT_SYMBOL(simple_commit_write);
 626 EXPORT_SYMBOL(simple_dir_inode_operations);
 627 EXPORT_SYMBOL(simple_dir_operations);
 628 EXPORT_SYMBOL(simple_empty);
 629 EXPORT_SYMBOL(d_alloc_name);
 630 EXPORT_SYMBOL(simple_fill_super);
 631 EXPORT_SYMBOL(simple_getattr);
 632 EXPORT_SYMBOL(simple_link);
 633 EXPORT_SYMBOL(simple_lookup);
 634 EXPORT_SYMBOL(simple_pin_fs);
 635 EXPORT_SYMBOL(simple_prepare_write);
 636 EXPORT_SYMBOL(simple_readpage);
 637 EXPORT_SYMBOL(simple_release_fs);
 638 EXPORT_SYMBOL(simple_rename);
 639 EXPORT_SYMBOL(simple_rmdir);
 640 EXPORT_SYMBOL(simple_statfs);
 641 EXPORT_SYMBOL(simple_sync_file);
 642 EXPORT_SYMBOL(simple_unlink);
 643 EXPORT_SYMBOL(simple_read_from_buffer);
 644 EXPORT_SYMBOL(simple_transaction_get);
 645 EXPORT_SYMBOL(simple_transaction_read);
 646 EXPORT_SYMBOL(simple_transaction_release);
 647 EXPORT_SYMBOL_GPL(simple_attr_open);
 648 EXPORT_SYMBOL_GPL(simple_attr_close);
 649 EXPORT_SYMBOL_GPL(simple_attr_read);
 650 EXPORT_SYMBOL_GPL(simple_attr_write);