fs/read_write.c

   1 /*
   2  *  linux/fs/read_write.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 #include <linux/slab.h>
   8 #include <linux/stat.h>
   9 #include <linux/fcntl.h>
  10 #include <linux/file.h>
  11 #include <linux/uio.h>
  12 #include <linux/smp_lock.h>
  13 #include <linux/fsnotify.h>
  14 #include <linux/security.h>
  15 #include <linux/module.h>
  16 #include <linux/syscalls.h>
  17
  18 #include <asm/uaccess.h>
  19 #include <asm/unistd.h>
  20
  21 struct file_operations generic_ro_fops = {
  22         .llseek         = generic_file_llseek,
  23         .read           = generic_file_read,
  24         .mmap           = generic_file_readonly_mmap,
  25         .sendfile       = generic_file_sendfile,
  26 };
  27
  28 EXPORT_SYMBOL(generic_ro_fops);
  29
  30 loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
  31 {
  32         long long retval;
  33         struct inode *inode = file->f_mapping->host;
  34
  35         down(&inode->i_sem);
  36         switch (origin) {
  37                 case 2:
  38                         offset += inode->i_size;
  39                         break;
  40                 case 1:
  41                         offset += file->f_pos;
  42         }
  43         retval = -EINVAL;
  44         if (offset>=0 && offset<=inode->i_sb->s_maxbytes) {
  45                 if (offset != file->f_pos) {
  46                         file->f_pos = offset;
  47                         file->f_version = 0;
  48                 }
  49                 retval = offset;
  50         }
  51         up(&inode->i_sem);
  52         return retval;
  53 }
  54
  55 EXPORT_SYMBOL(generic_file_llseek);
  56
  57 loff_t remote_llseek(struct file *file, loff_t offset, int origin)
  58 {
  59         long long retval;
  60
  61         lock_kernel();
  62         switch (origin) {
  63                 case 2:
  64                         offset += i_size_read(file->f_dentry->d_inode);
  65                         break;
  66                 case 1:
  67                         offset += file->f_pos;
  68         }
  69         retval = -EINVAL;
  70         if (offset>=0 && offset<=file->f_dentry->d_inode->i_sb->s_maxbytes) {
  71                 if (offset != file->f_pos) {
  72                         file->f_pos = offset;
  73                         file->f_version = 0;
  74                 }
  75                 retval = offset;
  76         }
  77         unlock_kernel();
  78         return retval;
  79 }
  80 EXPORT_SYMBOL(remote_llseek);
  81
  82 loff_t no_llseek(struct file *file, loff_t offset, int origin)
  83 {
  84         return -ESPIPE;
  85 }
  86 EXPORT_SYMBOL(no_llseek);
  87
  88 loff_t default_llseek(struct file *file, loff_t offset, int origin)
  89 {
  90         long long retval;
  91
  92         lock_kernel();
  93         switch (origin) {
  94                 case 2:
  95                         offset += i_size_read(file->f_dentry->d_inode);
  96                         break;
  97                 case 1:
  98                         offset += file->f_pos;
  99         }
 100         retval = -EINVAL;
 101         if (offset >= 0) {
 102                 if (offset != file->f_pos) {
 103                         file->f_pos = offset;
 104                         file->f_version = 0;
 105                 }
 106                 retval = offset;
 107         }
 108         unlock_kernel();
 109         return retval;
 110 }
 111 EXPORT_SYMBOL(default_llseek);
 112
 113 loff_t vfs_llseek(struct file *file, loff_t offset, int origin)
 114 {
 115         loff_t (*fn)(struct file *, loff_t, int);
 116
 117         fn = no_llseek;
 118         if (file->f_mode & FMODE_LSEEK) {
 119                 fn = default_llseek;
 120                 if (file->f_op && file->f_op->llseek)
 121                         fn = file->f_op->llseek;
 122         }
 123         return fn(file, offset, origin);
 124 }
 125 EXPORT_SYMBOL(vfs_llseek);
 126
 127 asmlinkage off_t sys_lseek(unsigned int fd, off_t offset, unsigned int origin)
 128 {
 129         off_t retval;
 130         struct file * file;
 131         int fput_needed;
 132
 133         retval = -EBADF;
 134         file = fget_light(fd, &fput_needed);
 135         if (!file)
 136                 goto bad;
 137
 138         retval = -EINVAL;
 139         if (origin <= 2) {
 140                 loff_t res = vfs_llseek(file, offset, origin);
 141                 retval = res;
 142                 if (res != (loff_t)retval)
 143                         retval = -EOVERFLOW;    /* LFS: should only happen on 32 bit platforms */
 144         }
 145         fput_light(file, fput_needed);
 146 bad:
 147         return retval;
 148 }
 149
 150 #ifdef __ARCH_WANT_SYS_LLSEEK
 151 asmlinkage long sys_llseek(unsigned int fd, unsigned long offset_high,
 152                            unsigned long offset_low, loff_t __user * result,
 153                            unsigned int origin)
 154 {
 155         int retval;
 156         struct file * file;
 157         loff_t offset;
 158         int fput_needed;
 159
 160         retval = -EBADF;
 161         file = fget_light(fd, &fput_needed);
 162         if (!file)
 163                 goto bad;
 164
 165         retval = -EINVAL;
 166         if (origin > 2)
 167                 goto out_putf;
 168
 169         offset = vfs_llseek(file, ((loff_t) offset_high << 32) | offset_low,
 170                         origin);
 171
 172         retval = (int)offset;
 173         if (offset >= 0) {
 174                 retval = -EFAULT;
 175                 if (!copy_to_user(result, &offset, sizeof(offset)))
 176                         retval = 0;
 177         }
 178 out_putf:
 179         fput_light(file, fput_needed);
 180 bad:
 181         return retval;
 182 }
 183 #endif
 184
 185
 186 int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count)
 187 {
 188         struct inode *inode;
 189         loff_t pos;
 190
 191         if (unlikely(count > INT_MAX))
 192                 goto Einval;
 193         pos = *ppos;
 194         if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
 195                 goto Einval;
 196
 197         inode = file->f_dentry->d_inode;
 198         if (inode->i_flock && MANDATORY_LOCK(inode))
 199                 return locks_mandatory_area(read_write == READ ? FLOCK_VERIFY_READ : FLOCK_VERIFY_WRITE, inode, file, pos, count);
 200         return 0;
 201
 202 Einval:
 203         return -EINVAL;
 204 }
 205
 206 static void wait_on_retry_sync_kiocb(struct kiocb *iocb)
 207 {
 208         set_current_state(TASK_UNINTERRUPTIBLE);
 209         if (!kiocbIsKicked(iocb))
 210                 schedule();
 211         else
 212                 kiocbClearKicked(iocb);
 213         __set_current_state(TASK_RUNNING);
 214 }
 215
 216 ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
 217 {
 218         struct kiocb kiocb;
 219         ssize_t ret;
 220
 221         init_sync_kiocb(&kiocb, filp);
 222         kiocb.ki_pos = *ppos;
 223         while (-EIOCBRETRY ==
 224                 (ret = filp->f_op->aio_read(&kiocb, buf, len, kiocb.ki_pos)))
 225                 wait_on_retry_sync_kiocb(&kiocb);
 226
 227         if (-EIOCBQUEUED == ret)
 228                 ret = wait_on_sync_kiocb(&kiocb);
 229         *ppos = kiocb.ki_pos;
 230         return ret;
 231 }
 232
 233 EXPORT_SYMBOL(do_sync_read);
 234
 235 ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
 236 {
 237         ssize_t ret;
 238
 239         if (!(file->f_mode & FMODE_READ))
 240                 return -EBADF;
 241         if (!file->f_op || (!file->f_op->read && !file->f_op->aio_read))
 242                 return -EINVAL;
 243         if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))
 244                 return -EFAULT;
 245
 246         ret = rw_verify_area(READ, file, pos, count);
 247         if (!ret) {
 248                 ret = security_file_permission (file, MAY_READ);
 249                 if (!ret) {
 250                         if (file->f_op->read)
 251                                 ret = file->f_op->read(file, buf, count, pos);
 252                         else
 253                                 ret = do_sync_read(file, buf, count, pos);
 254                         if (ret > 0) {
 255                                 fsnotify_access(file->f_dentry);
 256                                 current->rchar += ret;
 257                         }
 258                         current->syscr++;
 259                 }
 260         }
 261
 262         return ret;
 263 }
 264
 265 EXPORT_SYMBOL(vfs_read);
 266
 267 ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos)
 268 {
 269         struct kiocb kiocb;
 270         ssize_t ret;
 271
 272         init_sync_kiocb(&kiocb, filp);
 273         kiocb.ki_pos = *ppos;
 274         while (-EIOCBRETRY ==
 275                (ret = filp->f_op->aio_write(&kiocb, buf, len, kiocb.ki_pos)))
 276                 wait_on_retry_sync_kiocb(&kiocb);
 277
 278         if (-EIOCBQUEUED == ret)
 279                 ret = wait_on_sync_kiocb(&kiocb);
 280         *ppos = kiocb.ki_pos;
 281         return ret;
 282 }
 283
 284 EXPORT_SYMBOL(do_sync_write);
 285
 286 ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
 287 {
 288         ssize_t ret;
 289
 290         if (!(file->f_mode & FMODE_WRITE))
 291                 return -EBADF;
 292         if (!file->f_op || (!file->f_op->write && !file->f_op->aio_write))
 293                 return -EINVAL;
 294         if (unlikely(!access_ok(VERIFY_READ, buf, count)))
 295                 return -EFAULT;
 296
 297         ret = rw_verify_area(WRITE, file, pos, count);
 298         if (!ret) {
 299                 ret = security_file_permission (file, MAY_WRITE);
 300                 if (!ret) {
 301                         if (file->f_op->write)
 302                                 ret = file->f_op->write(file, buf, count, pos);
 303                         else
 304                                 ret = do_sync_write(file, buf, count, pos);
 305                         if (ret > 0) {
 306                                 fsnotify_modify(file->f_dentry);
 307                                 current->wchar += ret;
 308                         }
 309                         current->syscw++;
 310                 }
 311         }
 312
 313         return ret;
 314 }
 315
 316 EXPORT_SYMBOL(vfs_write);
 317
 318 static inline loff_t file_pos_read(struct file *file)
 319 {
 320         return file->f_pos;
 321 }
 322
 323 static inline void file_pos_write(struct file *file, loff_t pos)
 324 {
 325         file->f_pos = pos;
 326 }
 327
 328 asmlinkage ssize_t sys_read(unsigned int fd, char __user * buf, size_t count)
 329 {
 330         struct file *file;
 331         ssize_t ret = -EBADF;
 332         int fput_needed;
 333
 334         file = fget_light(fd, &fput_needed);
 335         if (file) {
 336                 loff_t pos = file_pos_read(file);
 337                 ret = vfs_read(file, buf, count, &pos);
 338                 file_pos_write(file, pos);
 339                 fput_light(file, fput_needed);
 340         }
 341
 342         return ret;
 343 }
 344 EXPORT_SYMBOL_GPL(sys_read);
 345
 346 asmlinkage ssize_t sys_write(unsigned int fd, const char __user * buf, size_t count)
 347 {
 348         struct file *file;
 349         ssize_t ret = -EBADF;
 350         int fput_needed;
 351
 352         file = fget_light(fd, &fput_needed);
 353         if (file) {
 354                 loff_t pos = file_pos_read(file);
 355                 ret = vfs_write(file, buf, count, &pos);
 356                 file_pos_write(file, pos);
 357                 fput_light(file, fput_needed);
 358         }
 359
 360         return ret;
 361 }
 362
 363 asmlinkage ssize_t sys_pread64(unsigned int fd, char __user *buf,
 364                              size_t count, loff_t pos)
 365 {
 366         struct file *file;
 367         ssize_t ret = -EBADF;
 368         int fput_needed;
 369
 370         if (pos < 0)
 371                 return -EINVAL;
 372
 373         file = fget_light(fd, &fput_needed);
 374         if (file) {
 375                 ret = -ESPIPE;
 376                 if (file->f_mode & FMODE_PREAD)
 377                         ret = vfs_read(file, buf, count, &pos);
 378                 fput_light(file, fput_needed);
 379         }
 380
 381         return ret;
 382 }
 383
 384 asmlinkage ssize_t sys_pwrite64(unsigned int fd, const char __user *buf,
 385                               size_t count, loff_t pos)
 386 {
 387         struct file *file;
 388         ssize_t ret = -EBADF;
 389         int fput_needed;
 390
 391         if (pos < 0)
 392                 return -EINVAL;
 393
 394         file = fget_light(fd, &fput_needed);
 395         if (file) {
 396                 ret = -ESPIPE;
 397                 if (file->f_mode & FMODE_PWRITE)
 398                         ret = vfs_write(file, buf, count, &pos);
 399                 fput_light(file, fput_needed);
 400         }
 401
 402         return ret;
 403 }
 404
 405 /*
 406  * Reduce an iovec's length in-place.  Return the resulting number of segments
 407  */
 408 unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to)
 409 {
 410         unsigned long seg = 0;
 411         size_t len = 0;
 412
 413         while (seg < nr_segs) {
 414                 seg++;
 415                 if (len + iov->iov_len >= to) {
 416                         iov->iov_len = to - len;
 417                         break;
 418                 }
 419                 len += iov->iov_len;
 420                 iov++;
 421         }
 422         return seg;
 423 }
 424
 425 EXPORT_SYMBOL(iov_shorten);
 426
 427 /* A write operation does a read from user space and vice versa */
 428 #define vrfy_dir(type) ((type) == READ ? VERIFY_WRITE : VERIFY_READ)
 429
 430 static ssize_t do_readv_writev(int type, struct file *file,
 431                                const struct iovec __user * uvector,
 432                                unsigned long nr_segs, loff_t *pos)
 433 {
 434         typedef ssize_t (*io_fn_t)(struct file *, char __user *, size_t, loff_t *);
 435         typedef ssize_t (*iov_fn_t)(struct file *, const struct iovec *, unsigned long, loff_t *);
 436
 437         size_t tot_len;
 438         struct iovec iovstack[UIO_FASTIOV];
 439         struct iovec *iov=iovstack, *vector;
 440         ssize_t ret;
 441         int seg;
 442         io_fn_t fn;
 443         iov_fn_t fnv;
 444
 445         /*
 446          * SuS says "The readv() function *may* fail if the iovcnt argument
 447          * was less than or equal to 0, or greater than {IOV_MAX}.  Linux has
 448          * traditionally returned zero for zero segments, so...
 449          */
 450         ret = 0;
 451         if (nr_segs == 0)
 452                 goto out;
 453
 454         /*
 455          * First get the "struct iovec" from user memory and
 456          * verify all the pointers
 457          */
 458         ret = -EINVAL;
 459         if ((nr_segs > UIO_MAXIOV) || (nr_segs <= 0))
 460                 goto out;
 461         if (!file->f_op)
 462                 goto out;
 463         if (nr_segs > UIO_FASTIOV) {
 464                 ret = -ENOMEM;
 465                 iov = kmalloc(nr_segs*sizeof(struct iovec), GFP_KERNEL);
 466                 if (!iov)
 467                         goto out;
 468         }
 469         ret = -EFAULT;
 470         if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector)))
 471                 goto out;
 472
 473         /*
 474          * Single unix specification:
 475          * We should -EINVAL if an element length is not >= 0 and fitting an
 476          * ssize_t.  The total length is fitting an ssize_t
 477          *
 478          * Be careful here because iov_len is a size_t not an ssize_t
 479          */
 480         tot_len = 0;
 481         ret = -EINVAL;
 482         for (seg = 0; seg < nr_segs; seg++) {
 483                 void __user *buf = iov[seg].iov_base;
 484                 ssize_t len = (ssize_t)iov[seg].iov_len;
 485
 486                 if (len < 0)    /* size_t not fitting an ssize_t .. */
 487                         goto out;
 488                 if (unlikely(!access_ok(vrfy_dir(type), buf, len)))
 489                         goto Efault;
 490                 tot_len += len;
 491                 if ((ssize_t)tot_len < 0) /* maths overflow on the ssize_t */
 492                         goto out;
 493         }
 494         if (tot_len == 0) {
 495                 ret = 0;
 496                 goto out;
 497         }
 498
 499         ret = rw_verify_area(type, file, pos, tot_len);
 500         if (ret)
 501                 goto out;
 502
 503         fnv = NULL;
 504         if (type == READ) {
 505                 fn = file->f_op->read;
 506                 fnv = file->f_op->readv;
 507         } else {
 508                 fn = (io_fn_t)file->f_op->write;
 509                 fnv = file->f_op->writev;
 510         }
 511         if (fnv) {
 512                 ret = fnv(file, iov, nr_segs, pos);
 513                 goto out;
 514         }
 515
 516         /* Do it by hand, with file-ops */
 517         ret = 0;
 518         vector = iov;
 519         while (nr_segs > 0) {
 520                 void __user * base;
 521                 size_t len;
 522                 ssize_t nr;
 523
 524                 base = vector->iov_base;
 525                 len = vector->iov_len;
 526                 vector++;
 527                 nr_segs--;
 528
 529                 nr = fn(file, base, len, pos);
 530
 531                 if (nr < 0) {
 532                         if (!ret) ret = nr;
 533                         break;
 534                 }
 535                 ret += nr;
 536                 if (nr != len)
 537                         break;
 538         }
 539 out:
 540         if (iov != iovstack)
 541                 kfree(iov);
 542         if ((ret + (type == READ)) > 0) {
 543                 if (type == READ)
 544                         fsnotify_access(file->f_dentry);
 545                 else
 546                         fsnotify_modify(file->f_dentry);
 547         }
 548         return ret;
 549 Efault:
 550         ret = -EFAULT;
 551         goto out;
 552 }
 553
 554 ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 555                   unsigned long vlen, loff_t *pos)
 556 {
 557         if (!(file->f_mode & FMODE_READ))
 558                 return -EBADF;
 559         if (!file->f_op || (!file->f_op->readv && !file->f_op->read))
 560                 return -EINVAL;
 561
 562         return do_readv_writev(READ, file, vec, vlen, pos);
 563 }
 564
 565 EXPORT_SYMBOL(vfs_readv);
 566
 567 ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
 568                    unsigned long vlen, loff_t *pos)
 569 {
 570         if (!(file->f_mode & FMODE_WRITE))
 571                 return -EBADF;
 572         if (!file->f_op || (!file->f_op->writev && !file->f_op->write))
 573                 return -EINVAL;
 574
 575         return do_readv_writev(WRITE, file, vec, vlen, pos);
 576 }
 577
 578 EXPORT_SYMBOL(vfs_writev);
 579
 580 asmlinkage ssize_t
 581 sys_readv(unsigned long fd, const struct iovec __user *vec, unsigned long vlen)
 582 {
 583         struct file *file;
 584         ssize_t ret = -EBADF;
 585         int fput_needed;
 586
 587         file = fget_light(fd, &fput_needed);
 588         if (file) {
 589                 loff_t pos = file_pos_read(file);
 590                 ret = vfs_readv(file, vec, vlen, &pos);
 591                 file_pos_write(file, pos);
 592                 fput_light(file, fput_needed);
 593         }
 594
 595         if (ret > 0)
 596                 current->rchar += ret;
 597         current->syscr++;
 598         return ret;
 599 }
 600
 601 asmlinkage ssize_t
 602 sys_writev(unsigned long fd, const struct iovec __user *vec, unsigned long vlen)
 603 {
 604         struct file *file;
 605         ssize_t ret = -EBADF;
 606         int fput_needed;
 607
 608         file = fget_light(fd, &fput_needed);
 609         if (file) {
 610                 loff_t pos = file_pos_read(file);
 611                 ret = vfs_writev(file, vec, vlen, &pos);
 612                 file_pos_write(file, pos);
 613                 fput_light(file, fput_needed);
 614         }
 615
 616         if (ret > 0)
 617                 current->wchar += ret;
 618         current->syscw++;
 619         return ret;
 620 }
 621
 622 static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
 623                            size_t count, loff_t max)
 624 {
 625         struct file * in_file, * out_file;
 626         struct inode * in_inode, * out_inode;
 627         loff_t pos;
 628         ssize_t retval;
 629         int fput_needed_in, fput_needed_out;
 630
 631         /*
 632          * Get input file, and verify that it is ok..
 633          */
 634         retval = -EBADF;
 635         in_file = fget_light(in_fd, &fput_needed_in);
 636         if (!in_file)
 637                 goto out;
 638         if (!(in_file->f_mode & FMODE_READ))
 639                 goto fput_in;
 640         retval = -EINVAL;
 641         in_inode = in_file->f_dentry->d_inode;
 642         if (!in_inode)
 643                 goto fput_in;
 644         if (!in_file->f_op || !in_file->f_op->sendfile)
 645                 goto fput_in;
 646         retval = -ESPIPE;
 647         if (!ppos)
 648                 ppos = &in_file->f_pos;
 649         else
 650                 if (!(in_file->f_mode & FMODE_PREAD))
 651                         goto fput_in;
 652         retval = rw_verify_area(READ, in_file, ppos, count);
 653         if (retval)
 654                 goto fput_in;
 655
 656         retval = security_file_permission (in_file, MAY_READ);
 657         if (retval)
 658                 goto fput_in;
 659
 660         /*
 661          * Get output file, and verify that it is ok..
 662          */
 663         retval = -EBADF;
 664         out_file = fget_light(out_fd, &fput_needed_out);
 665         if (!out_file)
 666                 goto fput_in;
 667         if (!(out_file->f_mode & FMODE_WRITE))
 668                 goto fput_out;
 669         retval = -EINVAL;
 670         if (!out_file->f_op || !out_file->f_op->sendpage)
 671                 goto fput_out;
 672         out_inode = out_file->f_dentry->d_inode;
 673         retval = rw_verify_area(WRITE, out_file, &out_file->f_pos, count);
 674         if (retval)
 675                 goto fput_out;
 676
 677         retval = security_file_permission (out_file, MAY_WRITE);
 678         if (retval)
 679                 goto fput_out;
 680
 681         if (!max)
 682                 max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
 683
 684         pos = *ppos;
 685         retval = -EINVAL;
 686         if (unlikely(pos < 0))
 687                 goto fput_out;
 688         if (unlikely(pos + count > max)) {
 689                 retval = -EOVERFLOW;
 690                 if (pos >= max)
 691                         goto fput_out;
 692                 count = max - pos;
 693         }
 694
 695         retval = in_file->f_op->sendfile(in_file, ppos, count, file_send_actor, out_file);
 696
 697         if (retval > 0) {
 698                 current->rchar += retval;
 699                 current->wchar += retval;
 700         }
 701         current->syscr++;
 702         current->syscw++;
 703
 704         if (*ppos > max)
 705                 retval = -EOVERFLOW;
 706
 707 fput_out:
 708         fput_light(out_file, fput_needed_out);
 709 fput_in:
 710         fput_light(in_file, fput_needed_in);
 711 out:
 712         return retval;
 713 }
 714
 715 asmlinkage ssize_t sys_sendfile(int out_fd, int in_fd, off_t __user *offset, size_t count)
 716 {
 717         loff_t pos;
 718         off_t off;
 719         ssize_t ret;
 720
 721         if (offset) {
 722                 if (unlikely(get_user(off, offset)))
 723                         return -EFAULT;
 724                 pos = off;
 725                 ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
 726                 if (unlikely(put_user(pos, offset)))
 727                         return -EFAULT;
 728                 return ret;
 729         }
 730
 731         return do_sendfile(out_fd, in_fd, NULL, count, 0);
 732 }
 733
 734 asmlinkage ssize_t sys_sendfile64(int out_fd, int in_fd, loff_t __user *offset, size_t count)
 735 {
 736         loff_t pos;
 737         ssize_t ret;
 738
 739         if (offset) {
 740                 if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
 741                         return -EFAULT;
 742                 ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
 743                 if (unlikely(put_user(pos, offset)))
 744                         return -EFAULT;
 745                 return ret;
 746         }
 747
 748         return do_sendfile(out_fd, in_fd, NULL, count, 0);
 749 }