netdev - Re: [PATCH net v4 2/2] mptcp: count CLOSE-WAIT sockets for MPTCP_MIB

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Date: Mon, 3 Jun 2024 23:04:53 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	davem@...emloft.net, dsahern@...nel.org, martineau@...nel.org, 
	geliang@...nel.org, netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net v4 2/2] mptcp: count CLOSE-WAIT sockets for MPTCP_MIB_CURRESTAB

Hi Matthieu,

On Mon, Jun 3, 2024 at 9:57 PM Matthieu Baerts <matttbe@...nel.org> wrote:
>
> Hi Jason,
>
> On 03/06/2024 15:26, Jason Xing wrote:
> > Hello Matthieu,
> >
> > On Mon, Jun 3, 2024 at 8:47 PM Matthieu Baerts <matttbe@...nel.org> wrote:
> >>
> >> Hi Jason,
> >>
> >> On 31/05/2024 11:17, Jason Xing wrote:
> >>> From: Jason Xing <kernelxing@...cent.com>
> >>>
> >>> Like previous patch does in TCP, we need to adhere to RFC 1213:
> >>>
> >>>   "tcpCurrEstab OBJECT-TYPE
> >>>    ...
> >>>    The number of TCP connections for which the current state
> >>>    is either ESTABLISHED or CLOSE- WAIT."
> >>>
> >>> So let's consider CLOSE-WAIT sockets.
> >>>
> >>> The logic of counting
> >>> When we increment the counter?
> >>> a) Only if we change the state to ESTABLISHED.
> >>>
> >>> When we decrement the counter?
> >>> a) if the socket leaves ESTABLISHED and will never go into CLOSE-WAIT,
> >>> say, on the client side, changing from ESTABLISHED to FIN-WAIT-1.
> >>> b) if the socket leaves CLOSE-WAIT, say, on the server side, changing
> >>> from CLOSE-WAIT to LAST-ACK.
> >>
> >> Thank you for this modification, and for having updated the Fixes tag.
> >>
> >>> Fixes: d9cd27b8cd19 ("mptcp: add CurrEstab MIB counter support")
> >>> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> >>> ---
> >>>  net/mptcp/protocol.c | 5 +++--
> >>>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> >>> index 7d44196ec5b6..6d59c1c4baba 100644
> >>> --- a/net/mptcp/protocol.c
> >>> +++ b/net/mptcp/protocol.c
> >>> @@ -2916,9 +2916,10 @@ void mptcp_set_state(struct sock *sk, int state)
> >>>               if (oldstate != TCP_ESTABLISHED)
> >>>                       MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
> >>>               break;
> >>> -
> >>> +     case TCP_CLOSE_WAIT:
> >>> +             break;
> >>
> >> The modification is correct: currently, and compared to TCP, the MPTCP
> >> "accepted" socket will not go through the TCP_SYN_RECV state because it
> >> will be created later on.
> >>
> >> Still, I wonder if it would not be clearer to explicitly mention this
> >> here, and (or) in the commit message, to be able to understand why the
> >> logic is different here, compared to TCP. I don't think the SYN_RECV
> >> state will be used in the future with MPTCP sockets, but just in case,
> >> it might help to mention TCP_SYN_RECV state here. Could add a small
> >> comment here above please?
> >
> > Sure, but what comments do you suggest?
> > For example, the comment above the case statement is:
> > "Unlike TCP, MPTCP would not have TCP_SYN_RECV state, so we can skip
> > it directly"
> > ?
> Yes, thank you, it looks good to me. But while at it, you can also add
> the reason:
>
>   case TCP_CLOSE_WAIT:
>           /* Unlike TCP, MPTCP sk would not have the TCP_SYN_RECV state:
>            * MPTCP "accepted" sockets will be created later on. So no
>            * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
>            */
>
> WDYT?

So great. Thank you. I will update it soon.

Thanks,
Jason

>
> Cheers,
> Matt
> --
> Sponsored by the NGI0 Core fund.
>