netdev - Re: [PATCH net-next 1/1] inet_diag: fetch cong algo info when socket is destroyed

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Message-Id: <20180429.203124.963666195389191670.davem@davemloft.net>
Date:   Sun, 29 Apr 2018 20:31:24 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jhs@...atatu.com
Cc:     kraig@...gle.com, netdev@...r.kernel.org, eric.dumazet@...il.com,
        kernel@...atatu.com, hadi@...atatu.com
Subject: Re: [PATCH net-next 1/1] inet_diag: fetch cong algo info when
 socket is destroyed

From: Jamal Hadi Salim <jhs@...atatu.com>
Date: Thu, 26 Apr 2018 13:58:05 -0400

> From: Jamal Hadi Salim <hadi@...atatu.com>
> 
> When a user dumps an existing established tcp socket state
> via inet diag, it is possible to retrieve the congestion control
> details.
> When an the sock is destroyed, the generated event has all the
> details available in the dump sans congestion control info.
> This patch fixes it.
> 
> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>

Well, two things:

1) The congestion control info is opt-in, meaning that the user gets
   it in the dump if they ask for it.

   This information is opt-in, because otherwise the dumps get really
   large.

   Therefore, emitting this stuff by default on destroys in a
   non-starter.

2) The TCP_TIME_WAIT test is not there for looks.  You need to add it
   also to the destroy case, and guess what?  All the sockets you will
   see will not pass that test.

I'm not applying this, sorry.  I really think things are go as-is, and
if you really truly want the congestion control information you can
ask for it while the socket is still alive, and is in the proper state
to sample the congestion control state before you kill it off.

Thanks.