libc/src/unistd/linux/isatty.cpp

   1 //===-- Linux implementation of isatty ------------------------------------===//
   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 #include "src/unistd/isatty.h"
  10
  11 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
  12 #include "src/__support/common.h"
  13
  14 #include "src/errno/libc_errno.h"
  15 #include <sys/ioctl.h>   // For ioctl numbers.
  16 #include <sys/syscall.h> // For syscall numbers.
  17
  18 namespace __llvm_libc {
  19
  20 LLVM_LIBC_FUNCTION(int, isatty, (int fd)) {
  21   constexpr int INIT_VAL = 0x1234abcd;
  22   int line_d_val = INIT_VAL;
  23   // This gets the line dicipline of the terminal. When called on something that
  24   // isn't a terminal it doesn't change line_d_val and returns -1.
  25   int result = __llvm_libc::syscall_impl(SYS_ioctl, fd, TIOCGETD, &line_d_val);
  26   if (result == 0)
  27     return 1;
  28
  29   libc_errno = -result;
  30   return 0;
  31 }
  32
  33 } // namespace __llvm_libc