line_buffer_writable
int32 line_buffer_writable(struct line_buffer &buffer);
&& line_buffer_writable(otherTTY->input_buffer) > 0) {
&& line_buffer_writable(tty->input_buffer) > 0)) {
size_t writable = line_buffer_writable(fTarget->input_buffer);
size_t locallyWritable = line_buffer_writable(fSource->input_buffer);
int32 writable = line_buffer_writable(tty->input_buffer);