libc/src/__support/File/linux/lseekImpl.h

   1 //===-- Linux implementation of lseek -------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H
  10 #define LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H
  11
  12 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
  13 #include "src/__support/common.h"
  14 #include "src/__support/error_or.h"
  15 #include "src/errno/libc_errno.h"
  16
  17 #include <stdint.h>      // For uint64_t.
  18 #include <sys/syscall.h> // For syscall numbers.
  19 #include <unistd.h>      // For off_t.
  20
  21 namespace LIBC_NAMESPACE {
  22 namespace internal {
  23
  24 LIBC_INLINE ErrorOr<off_t> lseekimpl(int fd, off_t offset, int whence) {
  25   off_t result;
  26 #ifdef SYS_lseek
  27   int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_lseek, fd, offset, whence);
  28   result = ret;
  29 #elif defined(SYS_llseek) || defined(SYS__llseek)
  30   static_assert(sizeof(size_t) == 4, "size_t must be 32 bits.");
  31 #ifdef SYS_llseek
  32   constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
  33 #elif defined(SYS__llseek)
  34   constexpr long LLSEEK_SYSCALL_NO = SYS__llseek;
  35 #endif
  36   off_t offset_64 = offset;
  37   int ret = LIBC_NAMESPACE::syscall_impl<int>(
  38       LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
  39 #else
  40 #error "lseek, llseek and _llseek syscalls not available."
  41 #endif
  42   if (ret < 0)
  43     return Error(-ret);
  44   return result;
  45 }
  46
  47 } // namespace internal
  48 } // namespace LIBC_NAMESPACE
  49
  50 #endif // LLVM_LIBC_SRC___SUPPORT_FILE_LINUX_LSEEKIMPL_H