Willy Tarreau <[email protected]> writes:
> Hi, > > On Wed, Mar 10, 2021 at 07:16:34PM +0100, Henneberg - Systemdesign wrote: >> 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? > > At least both man pages (tty_ioctl and tcp(7)) mention that TIOCOUTQ > should return the number of byte in queue. > > What I suspect for sockets is that sk_sndbuf grows with allocations > and that sk_wmem_alloc_get() in fact returns the number of unused > allocations thus the difference would be the amount queued. But I > could be wrong and I would tend to read the code the same way as you > did. I am quite sure that my assumption is right. When I call the ioctl right before and after writing data to an AF_BLUETOOTH socket the returned value decreases where it should increase. -Jochen > > Willy -- Henneberg - Systemdesign Jochen Henneberg Loehnfeld 26 21423 Winsen (Luhe) -- Fon: +49 172 160 14 69 www: www.henneberg-systemdesign.com
