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
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.
Willy
Willy Tarreau [off-list ref] writes:
Hi,
On Wed, Mar 10, 2021 at 07:16:34PM +0100, Henneberg - Systemdesign wrote:
quoted
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
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