sysdeps/unix/sysv/linux/lseek.c

   1 /* Linux lseek implementation, 32 bits off_t.
   2    Copyright (C) 2016-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library.  If not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <unistd.h>
  20 #include <stdint.h>
  21 #include <sys/types.h>
  22 #include <sysdep.h>
  23 #include <errno.h>
  24
  25 #ifndef __OFF_T_MATCHES_OFF64_T
  26
  27 /* Test for overflows of structures where we ask the kernel to fill them
  28    in with standard 64-bit syscalls but return them through APIs that
  29    only expose the low 32 bits of some fields.  */
  30
  31 static inline off_t lseek_overflow (loff_t res)
  32 {
  33   off_t retval = (off_t) res;
  34   if (retval == res)
  35     return retval;
  36
  37   __set_errno (EOVERFLOW);
  38   return (off_t) -1;
  39 }
  40
  41 off_t
  42 __lseek (int fd, off_t offset, int whence)
  43 {
  44 # ifdef __NR__llseek
  45   loff_t res;
  46   int rc = INLINE_SYSCALL_CALL (_llseek, fd,
  47                                 (long) (((uint64_t) (offset)) >> 32),
  48                                 (long) offset, &res, whence);
  49   return rc ?: lseek_overflow (res);
  50 # else
  51   return INLINE_SYSCALL_CALL (lseek, fd, offset, whence);
  52 # endif
  53 }
  54 libc_hidden_def (__lseek)
  55 weak_alias (__lseek, lseek)
  56 strong_alias (__lseek, __libc_lseek)
  57 #endif /* __OFF_T_MATCHES_OFF64_T  */