netdev - Re: [next] bonding: pass link-local packets to bonding master also.

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Date:   Sun, 09 Dec 2018 09:30:49 +0100
From:   Vincent Bernat <vincent@...nat.ch>
To:     Chonggang Li <chonggangli@...gle.com>
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Veaceslav Falico <vfalico@...il.com>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, Michal Soltys <soltys@....info>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Mahesh Bandewar <mahesh@...dewar.net>
Subject: Re: [next] bonding: pass link-local packets to bonding master also.

 ❦ 30 novembre 2018 22:32 +0100, Vincent Bernat <vincent@...nat.ch>:

>> Commit b89f04c61efe ("bonding: deliver link-local packets with
>> skb->dev set to link that packets arrived on") changed the behavior
>> of how link-local-multicast packets are processed. The change in
>> the behavior broke some legacy use cases where these packets are
>> expected to arrive on bonding master device also.
>
> Unfortunately, this doesn't completely restore the previous
> functionality as PACKET_ORIGDEV is broken for the copy: the original
> interface is lost through the call to netif_rx(). A LLDP daemon
> listening to the master interface won't get the original interface like
> it was able to before 4.12.

I think I didn't get an answer. The commit introducing the regression
says:

    Bonding driver changes the skb->dev to the bonding-master before
    passing the packet to stack for further processing. This, however
    does not make sense for the link-local packets and it loses "the
    link info" once its skb->dev is changed to bonding-master.  This
    patch changes this behavior for link-local packets by not changing
    the skb->dev to the bonding-master and maintaining it as it is,
    i.e. the link on which the packet arrived.

Li, do you have a test case for this? Which family are you using? When
using AF_PACKET, the information was retrievable by enabling the
PACKET_ORIGDEV option.

For context:

> I am a bit lost of what the original patch was trying to achieve. I am
> using the following test program:
>
> #v+
> #!/usr/bin/env python3
>
> import sys
> import socket
> import datetime
>
> socket.SOL_PACKET = 263
> socket.ETH_P_ALL = 3
> socket.PACKET_ORIGDEV = 9
>
> interface = sys.argv[1] if len(sys.argv) > 1 else 'lag1'
>
> s = socket.socket(socket.AF_PACKET,
>                   socket.SOCK_RAW,
>                   socket.htons(socket.ETH_P_ALL))
> s.bind((interface, 0))
> s.setsockopt(socket.SOL_PACKET, socket.PACKET_ORIGDEV, 1)
> while True:
>     data, addrinfo = s.recvfrom(1500)
>     if addrinfo[2] == socket.PACKET_OUTGOING:
>         continue
>     print(f"{datetime.datetime.now().isoformat()}: "
>           f"Received {len(data)} bytes from {addrinfo}")
> #v-
>
>
> If I run it with a kernel compiled with the commit before b89f04c61efe
> (plus a few more cherry-pick to make it work like ea8ffc0818d8 and
> 72ccc471e13b), I get:
>
> #v+
> 2018-11-30T22:20:40.193378: Received 221 bytes from ('eth1', 35020, 2, 1, b'RT3\x00\x00\x02')
> 2018-11-30T22:20:40.194504: Received 221 bytes from ('eth0', 35020, 2, 1, b'RT3\x00\x00\x01')
> #v-
>
>
> If I send non link-local packets, I get:
>
> #v+
> 2018-11-30T22:25:57.300965: Received 98 bytes from ('eth0', 2048, 0, 1, b'PT3\x00\x00\x02')
> #v-
>
> I am also able to correctly receive link-local packets directly on each
> interface. So, it seems everything was working as expected before
> b89f04c61efe.

-- 
This night methinks is but the daylight sick.
		-- William Shakespeare, "The Merchant of Venice"