#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <termios.h>

#include "../internal/syscall.h"

/*
 * isatty: report whether fildes is associated with a terminal.
 *
 * The probe is the kernel's own: issue the TCGETS ioctl, which a real
 * terminal answers with 0 and everything else rejects with -ENOTTY (a
 * regular file, directory, pipe, socket, or a character device that is
 * not a terminal such as /dev/null). A char-device fstat check is NOT
 * sufficient — /dev/null is a character device but not a tty — so the
 * ioctl is the correct test.
 *
 * The result is derived from the raw syscall return (negative -errno on
 * failure), so isatty never writes errno: POSIX permits an errno set on
 * a 0 return but does not require one, and skipping the write keeps the
 * probe free of thread-local side effects.
 */
int
isatty(int fildes)
{
    struct termios t;

    return __syscall3(SYS_ioctl, fildes, 0x5401 /* TCGETS */, (long)&t) == 0 ? 1 : 0;
}