netdev - Re: TPACKET_V3 timeout bug?

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Date:   Sat, 15 Apr 2017 18:45:36 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: TPACKET_V3 timeout bug?

On (04/15/17 21:40), Andrew Lunn wrote:
> 
> In my case, lan3 is up and idle, there are no packets flying around to
> be captured. So i would expect pcap_next_ex() to exit once a second,
> with a return value of 0. But it is not, it blocks and stays blocked.
   :
> Looking at the libpcap source, the 1000ms timeout is being used as
> part of the setsockopt(3, SOL_PACKET, PACKET_RX_RING, 0xbe9445c0, 28)
> call, req.tp_retire_blk_tov is set to the timeoutval.

right, aiui, the retire_blk_tov will only kick in if we have at
least one frame in a block, but the block is not filled up yet,
before the req.tp_retire_blk_tov (1s in your case) expires.

If there are 0 frames pending, we should not be waking up the app,
so everything seems to be behaving as it should?

--Sowmini