TIOCOUTQ implementation for sockets vs. tty

[Henneberg - Systemdesign]

Hi,

I have a question regarding the implementation of ioctl TIOCOUTQ for
various sockets compared to the tty implementation.

For several sockets, e. g. AF_BLUETOOTH it is done like this

af_bluetooth.c:
case TIOCOUTQ:
        if (sk->sk_state == BT_LISTEN)
                return -EINVAL;

        amount = sk->sk_sndbuf - sk_wmem_alloc_get(sk);
        if (amount < 0)
                amount = 0;
        err = put_user(amount, (int __user *)arg);
        break;

so the ioctl returns the available space in the send queue if I
understand the code correctly (this is also what I observed from tests).

The tty does this:

n_tty.c:
case TIOCOUTQ:
        return put_user(tty_chars_in_buffer(tty), (int __user *) arg);

so it returns the used space in the send queue. This is also what I
would expect from the manpage description.

Is this mismatch intentional?

Regards
-Jochen