Function ttyname

src/backend/linux_raw/termios/syscalls.rs:372–425

(fd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>])

#[cfg(feature = "alloc")]
#[cfg(feature = "fs")]
pub(crate) fn ttyname(fd: BorrowedFd<'_>, buf: &mut [MaybeUninit<u8>]) -> io::Result<usize> {
    let fd_stat = crate::backend::fs::syscalls::fstat(fd)?;

    // Quick check: if `fd` isn't a character device, it's not a tty.
    if FileType::from_raw_mode(fd_stat.st_mode) != FileType::CharacterDevice {
        return Err(io::Errno::NOTTY);
    }

    // Check that `fd` is really a tty.
    tcgetwinsize(fd)?;

    // Create the "/proc/self/fd/<fd>" string.
    let mut proc_self_fd_buf: [u8; 25] = *b"/proc/self/fd/\0\0\0\0\0\0\0\0\0\0\0";
    let dec_int = DecInt::from_fd(fd);
    let bytes_with_nul = dec_int.as_bytes_with_nul();
    proc_self_fd_buf[b"/proc/self/fd/".len()..][..bytes_with_nul.len()]
        .copy_from_slice(bytes_with_nul);

    // SAFETY: We just wrote a valid C String.
    let proc_self_fd_path = unsafe { CStr::from_ptr(proc_self_fd_buf.as_ptr().cast()) };

    let ptr = buf.as_mut_ptr();
    let len = {
        // Gather the ttyname by reading the "fd" file inside `proc_self_fd`.
        let (init, uninit) = crate::fs::readlinkat_raw(crate::fs::CWD, proc_self_fd_path, buf)?;

        // If the number of bytes is equal to the buffer length, truncation may
        // have occurred. This check also ensures that we have enough space for
        // adding a NUL terminator.
        if uninit.is_empty() {
            return Err(io::Errno::RANGE);
        }

        // `readlinkat` returns the number of bytes placed in the buffer.
        // NUL-terminate the string at that offset.
        uninit[0].write(b'\0');

        init.len()
    };

    // Check that the path we read refers to the same file as `fd`.
    {
        // SAFETY: We just wrote the NUL byte above.
        let path = unsafe { CStr::from_ptr(ptr.cast()) };

        let path_stat = crate::backend::fs::syscalls::stat(path)?;
        if path_stat.st_dev != fd_stat.st_dev || path_stat.st_ino != fd_stat.st_ino {
            return Err(io::Errno::NODEV);
        }
    }

    // Return the length, excluding the NUL terminator.
    Ok(len)
}