question wrt /drivers/char/tty_io.c in pre 2.6.16 code

Hi all,
In kernels prior to 2.6.16 it appears to me have
no mechanism for finding out if the tty recieve buffers
are full. This is important for me in implementing
flow control in the hso serial driver I'm developing
I don't want to lose characters.

The snippet from allesandro rubini's book
doesn't will just blindly flip buffers
& overrun if data is pushed in too quickly
into the tty layer. 

for (i = 0; i < data_size; ++i) {
if (tty->flip.count >= TTY_FLIPBUF_SIZE)
tty_flip_buffer_push(tty);
tty_insert_flip_char(tty, data[i], TTY_NORMAL);
}
tty_flip_buffer_push(tty);

The new tty_insert_flip_string returns the
number of bytes successfully copied to tty recieve buffers
how do I implement this functionality in pre 2.6.16 code,
can it be done?

Thank you,
D.J. Barrow