netdev - Re: [PATCH net-next] tcp: provide SYN headers for passive connections

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Date:	Mon, 4 May 2015 23:07:07 -0400
From:	John Heffner <johnwheffner@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Eric B Munson <emunson@...mai.com>,
	Tom Herbert <tom@...bertland.com>,
	"David S. Miller" <davem@...emloft.net>, linux-api@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] tcp: provide SYN headers for passive connections

On Mon, May 4, 2015 at 11:12 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2015-05-04 at 10:41 -0400, John Heffner wrote:
>
>> Nice idea, seems handy.  But a couple (somewhat related) questions:
>>
>> * Other than convenience, are there reasons not use an existing, more
>> general-purpose and portable mechanism like pcap?  (Permissions, I
>> guess?)
>
> Very hard to synchronize when say you have 32 listeners sharing a single
> port (SO_REUSEPORT), and receive one million SYN per second (when my TCP
> listener scaling work is finished).
>
> libpcap here would be a serious bottleneck, even with a clever FANIN
> support on the af_packet sockets, considering use of multiqueue NIC.
>
>> * Are there conditions where, for security purposes, you don't want an
>> application to have access to the raw SYNs?
>
> Not that we are aware of : We restrict the access to IP + TCP headers,
> for the passive part. All information that is available there was
> provided by the remote peer on a 'open way' anyway.

Makes sense, thanks.

  -John
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