netdev - Re: [PATCH V2 net-next 1/2] tcp: send in-queue bytes in cmsg upon read

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Message-Id: <20180430.115605.1094351453502803017.davem@davemloft.net>
Date:   Mon, 30 Apr 2018 11:56:05 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     soheil.kdev@...il.com, netdev@...r.kernel.org, ycheng@...gle.com,
        ncardwell@...gle.com, edumazet@...gle.com, willemb@...gle.com,
        soheil@...gle.com
Subject: Re: [PATCH V2 net-next 1/2] tcp: send in-queue bytes in cmsg upon
 read

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 30 Apr 2018 08:43:50 -0700

> I say sort of, because by the time we have any number, TCP might
> have received more packets anyway.

That's fine.

However, the number reported should have been true at least at some
finite point in time.

If you allow overlapping changes to either of the two variables during
the sampling, then you are reporting a number which was never true at
any point in time.

It is essentially garbage.