netdev - Re: [PATCH net-next 2/3] tcp: add newval parameter to tcp_rcvbuf

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Message-ID: <aab41dd0-2937-4d9f-a62a-60775243d6c4@redhat.com>
Date: Fri, 24 Oct 2025 15:50:02 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>, Simon Horman <horms@...nel.org>,
 Neal Cardwell <ncardwell@...gle.com>, Willem de Bruijn <willemb@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Matthieu Baerts <matttbe@...nel.org>,
 Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>,
 netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 2/3] tcp: add newval parameter to
 tcp_rcvbuf_grow()

On 10/24/25 1:19 PM, Eric Dumazet wrote:
> On Fri, Oct 24, 2025 at 3:09 AM Paolo Abeni <pabeni@...hat.com> wrote:
>> On 10/24/25 9:50 AM, Eric Dumazet wrote:
>>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
>>> index 94a5f6dcc5775e1265bb9f3c925fa80ae8c42924..2795acc96341765a3ec65657ec179cfd52ede483 100644
>>> --- a/net/mptcp/protocol.c
>>> +++ b/net/mptcp/protocol.c
>>> @@ -194,17 +194,19 @@ static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
>>>   * - mptcp does not maintain a msk-level window clamp
>>>   * - returns true when  the receive buffer is actually updated
>>>   */
>>> -static bool mptcp_rcvbuf_grow(struct sock *sk)
>>> +static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)
>>>  {
>>>       struct mptcp_sock *msk = mptcp_sk(sk);
>>>       const struct net *net = sock_net(sk);
>>> -     int rcvwin, rcvbuf, cap;
>>> +     u32 rcvwin, rcvbuf, cap, oldval;
>>>
>>> +     oldval = msk->rcvq_space.copied;
>>> +     msk->rcvq_space.copied = newval;
>>
>> I *think* the above should be:
>>
>>         oldval = msk->rcvq_space.space;
>>         msk->rcvq_space.space = newval;
>>
> 
> You are right, thanks for catching this.
> 
> I developed / tested this series on a kernel where MPTCP changes were
> not there yet.
> 
> Only when rebasing to net-next I realized MPTCP had to be changed.
> 
>> mptcp tracks the copied bytes incrementally - msk->rcvq_space.copied is
>> updated at each rcvmesg() iteration - and such difference IMHO makes
>> porting this kind of changes to mptcp a little more difficult.
>>
>> If you prefer, I can take care of the mptcp bits afterwards - I'll also
>> try to remove the mentioned difference and possibly move the algebra in
>> a common helper.
> 
> Do you want me to split this patch in two parts or is it okay if I
> send a V2 with
> the a/msk->rcvq_space.copied/msk->rcvq_space.space/ ?

I'm fine either way, please pick whatever fits you better. Given the
strict interconnection between this specific mptcp and tcp bits, and
thinking again about it, I now suspect splitting may harder and updating
the patch as described above could be the better option.

Thanks,

Paolo