fs/overlayfs/file.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2017 Red Hat, Inc.
   4  */
   5
   6 #include <linux/cred.h>
   7 #include <linux/file.h>
   8 #include <linux/mount.h>
   9 #include <linux/xattr.h>
  10 #include <linux/uio.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/splice.h>
  13 #include <linux/security.h>
  14 #include <linux/mm.h>
  15 #include <linux/fs.h>
  16 #include "overlayfs.h"
  17
  18 struct ovl_aio_req {
  19         struct kiocb iocb;
  20         refcount_t ref;
  21         struct kiocb *orig_iocb;
  22         struct fd fd;
  23 };
  24
  25 static struct kmem_cache *ovl_aio_request_cachep;
  26
  27 static char ovl_whatisit(struct inode *inode, struct inode *realinode)
  28 {
  29         if (realinode != ovl_inode_upper(inode))
  30                 return 'l';
  31         if (ovl_has_upperdata(inode))
  32                 return 'u';
  33         else
  34                 return 'm';
  35 }
  36
  37 /* No atime modificaton nor notify on underlying */
  38 #define OVL_OPEN_FLAGS (O_NOATIME | FMODE_NONOTIFY)
  39
  40 static struct file *ovl_open_realfile(const struct file *file,
  41                                       const struct path *realpath)
  42 {
  43         struct inode *realinode = d_inode(realpath->dentry);
  44         struct inode *inode = file_inode(file);
  45         struct user_namespace *real_mnt_userns;
  46         struct file *realfile;
  47         const struct cred *old_cred;
  48         int flags = file->f_flags | OVL_OPEN_FLAGS;
  49         int acc_mode = ACC_MODE(flags);
  50         int err;
  51
  52         if (flags & O_APPEND)
  53                 acc_mode |= MAY_APPEND;
  54
  55         old_cred = ovl_override_creds(inode->i_sb);
  56         real_mnt_userns = mnt_user_ns(realpath->mnt);
  57         err = inode_permission(real_mnt_userns, realinode, MAY_OPEN | acc_mode);
  58         if (err) {
  59                 realfile = ERR_PTR(err);
  60         } else {
  61                 if (!inode_owner_or_capable(real_mnt_userns, realinode))
  62                         flags &= ~O_NOATIME;
  63
  64                 realfile = open_with_fake_path(&file->f_path, flags, realinode,
  65                                                current_cred());
  66         }
  67         revert_creds(old_cred);
  68
  69         pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
  70                  file, file, ovl_whatisit(inode, realinode), file->f_flags,
  71                  realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
  72
  73         return realfile;
  74 }
  75
  76 #define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)
  77
  78 static int ovl_change_flags(struct file *file, unsigned int flags)
  79 {
  80         struct inode *inode = file_inode(file);
  81         int err;
  82
  83         flags &= OVL_SETFL_MASK;
  84
  85         if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
  86                 return -EPERM;
  87
  88         if ((flags & O_DIRECT) && !(file->f_mode & FMODE_CAN_ODIRECT))
  89                 return -EINVAL;
  90
  91         if (file->f_op->check_flags) {
  92                 err = file->f_op->check_flags(flags);
  93                 if (err)
  94                         return err;
  95         }
  96
  97         spin_lock(&file->f_lock);
  98         file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
  99         spin_unlock(&file->f_lock);
 100
 101         return 0;
 102 }
 103
 104 static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
 105                                bool allow_meta)
 106 {
 107         struct dentry *dentry = file_dentry(file);
 108         struct path realpath;
 109
 110         real->flags = 0;
 111         real->file = file->private_data;
 112
 113         if (allow_meta)
 114                 ovl_path_real(dentry, &realpath);
 115         else
 116                 ovl_path_realdata(dentry, &realpath);
 117
 118         /* Has it been copied up since we'd opened it? */
 119         if (unlikely(file_inode(real->file) != d_inode(realpath.dentry))) {
 120                 real->flags = FDPUT_FPUT;
 121                 real->file = ovl_open_realfile(file, &realpath);
 122
 123                 return PTR_ERR_OR_ZERO(real->file);
 124         }
 125
 126         /* Did the flags change since open? */
 127         if (unlikely((file->f_flags ^ real->file->f_flags) & ~OVL_OPEN_FLAGS))
 128                 return ovl_change_flags(real->file, file->f_flags);
 129
 130         return 0;
 131 }
 132
 133 static int ovl_real_fdget(const struct file *file, struct fd *real)
 134 {
 135         if (d_is_dir(file_dentry(file))) {
 136                 real->flags = 0;
 137                 real->file = ovl_dir_real_file(file, false);
 138
 139                 return PTR_ERR_OR_ZERO(real->file);
 140         }
 141
 142         return ovl_real_fdget_meta(file, real, false);
 143 }
 144
 145 static int ovl_open(struct inode *inode, struct file *file)
 146 {
 147         struct dentry *dentry = file_dentry(file);
 148         struct file *realfile;
 149         struct path realpath;
 150         int err;
 151
 152         err = ovl_maybe_copy_up(dentry, file->f_flags);
 153         if (err)
 154                 return err;
 155
 156         /* No longer need these flags, so don't pass them on to underlying fs */
 157         file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 158
 159         ovl_path_realdata(dentry, &realpath);
 160         realfile = ovl_open_realfile(file, &realpath);
 161         if (IS_ERR(realfile))
 162                 return PTR_ERR(realfile);
 163
 164         file->private_data = realfile;
 165
 166         return 0;
 167 }
 168
 169 static int ovl_release(struct inode *inode, struct file *file)
 170 {
 171         fput(file->private_data);
 172
 173         return 0;
 174 }
 175
 176 static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 177 {
 178         struct inode *inode = file_inode(file);
 179         struct fd real;
 180         const struct cred *old_cred;
 181         loff_t ret;
 182
 183         /*
 184          * The two special cases below do not need to involve real fs,
 185          * so we can optimizing concurrent callers.
 186          */
 187         if (offset == 0) {
 188                 if (whence == SEEK_CUR)
 189                         return file->f_pos;
 190
 191                 if (whence == SEEK_SET)
 192                         return vfs_setpos(file, 0, 0);
 193         }
 194
 195         ret = ovl_real_fdget(file, &real);
 196         if (ret)
 197                 return ret;
 198
 199         /*
 200          * Overlay file f_pos is the master copy that is preserved
 201          * through copy up and modified on read/write, but only real
 202          * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
 203          * limitations that are more strict than ->s_maxbytes for specific
 204          * files, so we use the real file to perform seeks.
 205          */
 206         ovl_inode_lock(inode);
 207         real.file->f_pos = file->f_pos;
 208
 209         old_cred = ovl_override_creds(inode->i_sb);
 210         ret = vfs_llseek(real.file, offset, whence);
 211         revert_creds(old_cred);
 212
 213         file->f_pos = real.file->f_pos;
 214         ovl_inode_unlock(inode);
 215
 216         fdput(real);
 217
 218         return ret;
 219 }
 220
 221 static void ovl_file_accessed(struct file *file)
 222 {
 223         struct inode *inode, *upperinode;
 224
 225         if (file->f_flags & O_NOATIME)
 226                 return;
 227
 228         inode = file_inode(file);
 229         upperinode = ovl_inode_upper(inode);
 230
 231         if (!upperinode)
 232                 return;
 233
 234         if ((!timespec64_equal(&inode->i_mtime, &upperinode->i_mtime) ||
 235              !timespec64_equal(&inode->i_ctime, &upperinode->i_ctime))) {
 236                 inode->i_mtime = upperinode->i_mtime;
 237                 inode->i_ctime = upperinode->i_ctime;
 238         }
 239
 240         touch_atime(&file->f_path);
 241 }
 242
 243 static rwf_t ovl_iocb_to_rwf(int ifl)
 244 {
 245         rwf_t flags = 0;
 246
 247         if (ifl & IOCB_NOWAIT)
 248                 flags |= RWF_NOWAIT;
 249         if (ifl & IOCB_HIPRI)
 250                 flags |= RWF_HIPRI;
 251         if (ifl & IOCB_DSYNC)
 252                 flags |= RWF_DSYNC;
 253         if (ifl & IOCB_SYNC)
 254                 flags |= RWF_SYNC;
 255
 256         return flags;
 257 }
 258
 259 static inline void ovl_aio_put(struct ovl_aio_req *aio_req)
 260 {
 261         if (refcount_dec_and_test(&aio_req->ref)) {
 262                 fdput(aio_req->fd);
 263                 kmem_cache_free(ovl_aio_request_cachep, aio_req);
 264         }
 265 }
 266
 267 static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
 268 {
 269         struct kiocb *iocb = &aio_req->iocb;
 270         struct kiocb *orig_iocb = aio_req->orig_iocb;
 271
 272         if (iocb->ki_flags & IOCB_WRITE) {
 273                 struct inode *inode = file_inode(orig_iocb->ki_filp);
 274
 275                 /* Actually acquired in ovl_write_iter() */
 276                 __sb_writers_acquired(file_inode(iocb->ki_filp)->i_sb,
 277                                       SB_FREEZE_WRITE);
 278                 file_end_write(iocb->ki_filp);
 279                 ovl_copyattr(inode);
 280         }
 281
 282         orig_iocb->ki_pos = iocb->ki_pos;
 283         ovl_aio_put(aio_req);
 284 }
 285
 286 static void ovl_aio_rw_complete(struct kiocb *iocb, long res)
 287 {
 288         struct ovl_aio_req *aio_req = container_of(iocb,
 289                                                    struct ovl_aio_req, iocb);
 290         struct kiocb *orig_iocb = aio_req->orig_iocb;
 291
 292         ovl_aio_cleanup_handler(aio_req);
 293         orig_iocb->ki_complete(orig_iocb, res);
 294 }
 295
 296 static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 297 {
 298         struct file *file = iocb->ki_filp;
 299         struct fd real;
 300         const struct cred *old_cred;
 301         ssize_t ret;
 302
 303         if (!iov_iter_count(iter))
 304                 return 0;
 305
 306         ret = ovl_real_fdget(file, &real);
 307         if (ret)
 308                 return ret;
 309
 310         ret = -EINVAL;
 311         if (iocb->ki_flags & IOCB_DIRECT &&
 312             !(real.file->f_mode & FMODE_CAN_ODIRECT))
 313                 goto out_fdput;
 314
 315         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 316         if (is_sync_kiocb(iocb)) {
 317                 ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
 318                                     ovl_iocb_to_rwf(iocb->ki_flags));
 319         } else {
 320                 struct ovl_aio_req *aio_req;
 321
 322                 ret = -ENOMEM;
 323                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 324                 if (!aio_req)
 325                         goto out;
 326
 327                 aio_req->fd = real;
 328                 real.flags = 0;
 329                 aio_req->orig_iocb = iocb;
 330                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 331                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 332                 refcount_set(&aio_req->ref, 2);
 333                 ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
 334                 ovl_aio_put(aio_req);
 335                 if (ret != -EIOCBQUEUED)
 336                         ovl_aio_cleanup_handler(aio_req);
 337         }
 338 out:
 339         revert_creds(old_cred);
 340         ovl_file_accessed(file);
 341 out_fdput:
 342         fdput(real);
 343
 344         return ret;
 345 }
 346
 347 static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 348 {
 349         struct file *file = iocb->ki_filp;
 350         struct inode *inode = file_inode(file);
 351         struct fd real;
 352         const struct cred *old_cred;
 353         ssize_t ret;
 354         int ifl = iocb->ki_flags;
 355
 356         if (!iov_iter_count(iter))
 357                 return 0;
 358
 359         inode_lock(inode);
 360         /* Update mode */
 361         ovl_copyattr(inode);
 362         ret = file_remove_privs(file);
 363         if (ret)
 364                 goto out_unlock;
 365
 366         ret = ovl_real_fdget(file, &real);
 367         if (ret)
 368                 goto out_unlock;
 369
 370         ret = -EINVAL;
 371         if (iocb->ki_flags & IOCB_DIRECT &&
 372             !(real.file->f_mode & FMODE_CAN_ODIRECT))
 373                 goto out_fdput;
 374
 375         if (!ovl_should_sync(OVL_FS(inode->i_sb)))
 376                 ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
 377
 378         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 379         if (is_sync_kiocb(iocb)) {
 380                 file_start_write(real.file);
 381                 ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
 382                                      ovl_iocb_to_rwf(ifl));
 383                 file_end_write(real.file);
 384                 /* Update size */
 385                 ovl_copyattr(inode);
 386         } else {
 387                 struct ovl_aio_req *aio_req;
 388
 389                 ret = -ENOMEM;
 390                 aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL);
 391                 if (!aio_req)
 392                         goto out;
 393
 394                 file_start_write(real.file);
 395                 /* Pacify lockdep, same trick as done in aio_write() */
 396                 __sb_writers_release(file_inode(real.file)->i_sb,
 397                                      SB_FREEZE_WRITE);
 398                 aio_req->fd = real;
 399                 real.flags = 0;
 400                 aio_req->orig_iocb = iocb;
 401                 kiocb_clone(&aio_req->iocb, iocb, real.file);
 402                 aio_req->iocb.ki_flags = ifl;
 403                 aio_req->iocb.ki_complete = ovl_aio_rw_complete;
 404                 refcount_set(&aio_req->ref, 2);
 405                 ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
 406                 ovl_aio_put(aio_req);
 407                 if (ret != -EIOCBQUEUED)
 408                         ovl_aio_cleanup_handler(aio_req);
 409         }
 410 out:
 411         revert_creds(old_cred);
 412 out_fdput:
 413         fdput(real);
 414
 415 out_unlock:
 416         inode_unlock(inode);
 417
 418         return ret;
 419 }
 420
 421 /*
 422  * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
 423  * due to lock order inversion between pipe->mutex in iter_file_splice_write()
 424  * and file_start_write(real.file) in ovl_write_iter().
 425  *
 426  * So do everything ovl_write_iter() does and call iter_file_splice_write() on
 427  * the real file.
 428  */
 429 static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 430                                 loff_t *ppos, size_t len, unsigned int flags)
 431 {
 432         struct fd real;
 433         const struct cred *old_cred;
 434         struct inode *inode = file_inode(out);
 435         ssize_t ret;
 436
 437         inode_lock(inode);
 438         /* Update mode */
 439         ovl_copyattr(inode);
 440         ret = file_remove_privs(out);
 441         if (ret)
 442                 goto out_unlock;
 443
 444         ret = ovl_real_fdget(out, &real);
 445         if (ret)
 446                 goto out_unlock;
 447
 448         old_cred = ovl_override_creds(inode->i_sb);
 449         file_start_write(real.file);
 450
 451         ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
 452
 453         file_end_write(real.file);
 454         /* Update size */
 455         ovl_copyattr(inode);
 456         revert_creds(old_cred);
 457         fdput(real);
 458
 459 out_unlock:
 460         inode_unlock(inode);
 461
 462         return ret;
 463 }
 464
 465 static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 466 {
 467         struct fd real;
 468         const struct cred *old_cred;
 469         int ret;
 470
 471         ret = ovl_sync_status(OVL_FS(file_inode(file)->i_sb));
 472         if (ret <= 0)
 473                 return ret;
 474
 475         ret = ovl_real_fdget_meta(file, &real, !datasync);
 476         if (ret)
 477                 return ret;
 478
 479         /* Don't sync lower file for fear of receiving EROFS error */
 480         if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 481                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 482                 ret = vfs_fsync_range(real.file, start, end, datasync);
 483                 revert_creds(old_cred);
 484         }
 485
 486         fdput(real);
 487
 488         return ret;
 489 }
 490
 491 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 492 {
 493         struct file *realfile = file->private_data;
 494         const struct cred *old_cred;
 495         int ret;
 496
 497         if (!realfile->f_op->mmap)
 498                 return -ENODEV;
 499
 500         if (WARN_ON(file != vma->vm_file))
 501                 return -EIO;
 502
 503         vma_set_file(vma, realfile);
 504
 505         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 506         ret = call_mmap(vma->vm_file, vma);
 507         revert_creds(old_cred);
 508         ovl_file_accessed(file);
 509
 510         return ret;
 511 }
 512
 513 static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 514 {
 515         struct inode *inode = file_inode(file);
 516         struct fd real;
 517         const struct cred *old_cred;
 518         int ret;
 519
 520         inode_lock(inode);
 521         /* Update mode */
 522         ovl_copyattr(inode);
 523         ret = file_remove_privs(file);
 524         if (ret)
 525                 goto out_unlock;
 526
 527         ret = ovl_real_fdget(file, &real);
 528         if (ret)
 529                 goto out_unlock;
 530
 531         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 532         ret = vfs_fallocate(real.file, mode, offset, len);
 533         revert_creds(old_cred);
 534
 535         /* Update size */
 536         ovl_copyattr(inode);
 537
 538         fdput(real);
 539
 540 out_unlock:
 541         inode_unlock(inode);
 542
 543         return ret;
 544 }
 545
 546 static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 547 {
 548         struct fd real;
 549         const struct cred *old_cred;
 550         int ret;
 551
 552         ret = ovl_real_fdget(file, &real);
 553         if (ret)
 554                 return ret;
 555
 556         old_cred = ovl_override_creds(file_inode(file)->i_sb);
 557         ret = vfs_fadvise(real.file, offset, len, advice);
 558         revert_creds(old_cred);
 559
 560         fdput(real);
 561
 562         return ret;
 563 }
 564
 565 enum ovl_copyop {
 566         OVL_COPY,
 567         OVL_CLONE,
 568         OVL_DEDUPE,
 569 };
 570
 571 static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 572                             struct file *file_out, loff_t pos_out,
 573                             loff_t len, unsigned int flags, enum ovl_copyop op)
 574 {
 575         struct inode *inode_out = file_inode(file_out);
 576         struct fd real_in, real_out;
 577         const struct cred *old_cred;
 578         loff_t ret;
 579
 580         inode_lock(inode_out);
 581         if (op != OVL_DEDUPE) {
 582                 /* Update mode */
 583                 ovl_copyattr(inode_out);
 584                 ret = file_remove_privs(file_out);
 585                 if (ret)
 586                         goto out_unlock;
 587         }
 588
 589         ret = ovl_real_fdget(file_out, &real_out);
 590         if (ret)
 591                 goto out_unlock;
 592
 593         ret = ovl_real_fdget(file_in, &real_in);
 594         if (ret) {
 595                 fdput(real_out);
 596                 goto out_unlock;
 597         }
 598
 599         old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
 600         switch (op) {
 601         case OVL_COPY:
 602                 ret = vfs_copy_file_range(real_in.file, pos_in,
 603                                           real_out.file, pos_out, len, flags);
 604                 break;
 605
 606         case OVL_CLONE:
 607                 ret = vfs_clone_file_range(real_in.file, pos_in,
 608                                            real_out.file, pos_out, len, flags);
 609                 break;
 610
 611         case OVL_DEDUPE:
 612                 ret = vfs_dedupe_file_range_one(real_in.file, pos_in,
 613                                                 real_out.file, pos_out, len,
 614                                                 flags);
 615                 break;
 616         }
 617         revert_creds(old_cred);
 618
 619         /* Update size */
 620         ovl_copyattr(inode_out);
 621
 622         fdput(real_in);
 623         fdput(real_out);
 624
 625 out_unlock:
 626         inode_unlock(inode_out);
 627
 628         return ret;
 629 }
 630
 631 static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
 632                                    struct file *file_out, loff_t pos_out,
 633                                    size_t len, unsigned int flags)
 634 {
 635         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
 636                             OVL_COPY);
 637 }
 638
 639 static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
 640                                    struct file *file_out, loff_t pos_out,
 641                                    loff_t len, unsigned int remap_flags)
 642 {
 643         enum ovl_copyop op;
 644
 645         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 646                 return -EINVAL;
 647
 648         if (remap_flags & REMAP_FILE_DEDUP)
 649                 op = OVL_DEDUPE;
 650         else
 651                 op = OVL_CLONE;
 652
 653         /*
 654          * Don't copy up because of a dedupe request, this wouldn't make sense
 655          * most of the time (data would be duplicated instead of deduplicated).
 656          */
 657         if (op == OVL_DEDUPE &&
 658             (!ovl_inode_upper(file_inode(file_in)) ||
 659              !ovl_inode_upper(file_inode(file_out))))
 660                 return -EPERM;
 661
 662         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
 663                             remap_flags, op);
 664 }
 665
 666 static int ovl_flush(struct file *file, fl_owner_t id)
 667 {
 668         struct fd real;
 669         const struct cred *old_cred;
 670         int err;
 671
 672         err = ovl_real_fdget(file, &real);
 673         if (err)
 674                 return err;
 675
 676         if (real.file->f_op->flush) {
 677                 old_cred = ovl_override_creds(file_inode(file)->i_sb);
 678                 err = real.file->f_op->flush(real.file, id);
 679                 revert_creds(old_cred);
 680         }
 681         fdput(real);
 682
 683         return err;
 684 }
 685
 686 const struct file_operations ovl_file_operations = {
 687         .open           = ovl_open,
 688         .release        = ovl_release,
 689         .llseek         = ovl_llseek,
 690         .read_iter      = ovl_read_iter,
 691         .write_iter     = ovl_write_iter,
 692         .fsync          = ovl_fsync,
 693         .mmap           = ovl_mmap,
 694         .fallocate      = ovl_fallocate,
 695         .fadvise        = ovl_fadvise,
 696         .flush          = ovl_flush,
 697         .splice_read    = generic_file_splice_read,
 698         .splice_write   = ovl_splice_write,
 699
 700         .copy_file_range        = ovl_copy_file_range,
 701         .remap_file_range       = ovl_remap_file_range,
 702 };
 703
 704 int __init ovl_aio_request_cache_init(void)
 705 {
 706         ovl_aio_request_cachep = kmem_cache_create("ovl_aio_req",
 707                                                    sizeof(struct ovl_aio_req),
 708                                                    0, SLAB_HWCACHE_ALIGN, NULL);
 709         if (!ovl_aio_request_cachep)
 710                 return -ENOMEM;
 711
 712         return 0;
 713 }
 714
 715 void ovl_aio_request_cache_destroy(void)
 716 {
 717         kmem_cache_destroy(ovl_aio_request_cachep);
 718 }