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 LIBC_NAMESPACE { 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 = 26 LIBC_NAMESPACE::syscall_impl<int>(SYS_ioctl, fd, TIOCGETD, &line_d_val); 27 if (result == 0) 28 return 1; 29 30 libc_errno = -result; 31 return 0; 32 } 33 34 } // namespace LIBC_NAMESPACE 35