netdev - Re: [PATCH net-next v5 05/11] tcp, ulp: Add clone operation to tcp_ulp

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Date:   Fri, 20 Dec 2019 17:21:19 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        netdev@...r.kernel.org, mptcp@...ts.01.org
Subject: Re: [PATCH net-next v5 05/11] tcp, ulp: Add clone operation to
 tcp_ulp_ops

On Fri, 2019-12-20 at 07:26 -0800, Eric Dumazet wrote:
> 
> On 12/19/19 2:34 PM, Mat Martineau wrote:
> > If ULP is used on a listening socket, icsk_ulp_ops and icsk_ulp_data are
> > copied when the listener is cloned. Sometimes the clone is immediately
> > deleted, which will invoke the release op on the clone and likely
> > corrupt the listening socket's icsk_ulp_data.
> > 
> > The clone operation is invoked immediately after the clone is copied and
> > gives the ULP type an opportunity to set up the clone socket and its
> > icsk_ulp_data.
> > 
> 
> Since the method is void, this means no error can happen.
> 
> For example we do not intend to attempt a memory allocation ?

if the MPTCP ULP clone fails, we fallback to plain TCP (the 'is_mptcp'
flag cleared on the tcp 'struct sock'), so we don't have an error
return code there.

If we change the 'clone' signature, than the only in-kernel user will
always return 0, would that be ok?

Thank you!

Paolo