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/__support/macros/config.h" 15 #include "src/errno/libc_errno.h" 16 #include <sys/ioctl.h> // For ioctl numbers. 17 #include <sys/syscall.h> // For syscall numbers. 18 19 namespace LIBC_NAMESPACE_DECL { 20 21 LLVM_LIBC_FUNCTION(int, isatty, (int fd)) { 22 constexpr int INIT_VAL = 0x1234abcd; 23 int line_d_val = INIT_VAL; 24 // This gets the line dicipline of the terminal. When called on something that 25 // isn't a terminal it doesn't change line_d_val and returns -1. 26 int result = 27 LIBC_NAMESPACE::syscall_impl<int>(SYS_ioctl, fd, TIOCGETD, &line_d_val); 28 if (result == 0) 29 return 1; 30 31 libc_errno = -result; 32 return 0; 33 } 34 35 } // namespace LIBC_NAMESPACE_DECL 36