netdev - Re: [PATCH net 1/1] bonding: fix PACKET_ORIGDEV regression on bonding masters

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Date:   Mon, 14 Jan 2019 08:00:24 +0000
From:   Vincent Bernat <vincent@...nat.ch>
To:     Maciej Żenczykowski <zenczykowski@...il.com>
Cc:     David Miller <davem@...emloft.net>, soltys@....info,
        Linux NetDev <netdev@...r.kernel.org>,
        Jay Vosburgh <jay.vosburgh@...onical.com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Chonggang Li <chonggangli@...gle.com>
Subject: Re: [PATCH net 1/1] bonding: fix PACKET_ORIGDEV regression on bonding masters

 ❦ 13 janvier 2019 18:01 -08, Maciej Żenczykowski <zenczykowski@...il.com>:

> But I seem to recall that the core problem we were trying to solve was
> that a daemon listening
> on an AF_PACKET ethertype 88CC [LLDP] socket not bound to any device
> would not receive LLDP packets
> arriving on inactive bond slaves (either active-backup or lag).

Just tested and with 4.9.150, I am in fact unable to receive anything
on a backup link when listening to the active-backup master device or to
"any" device.

> Perhaps going from:
>   /* don't change skb->dev for link-local packets */
>   if (is_link_local_ether_addr(eth_hdr(skb)->h_dest)) return RX_HANDLER_PASS;
>   if (bond_should_deliver_exact_match(skb, slave, bond)) return
> RX_HANDLER_EXACT;
>
> to something more like:
>   if (bond_should_deliver_exact_match(skb, slave, bond)) {
>     /* don't change skb->dev for link-local packets on inactive slaves */
>     if (is_link_local_ether_addr(eth_hdr(skb)->h_dest)) return RX_HANDLER_PASS;
>     return RX_HANDLER_EXACT;
>   }
>
> would fix both problems?

It makes PACKET_ORIGDEV works again. Moreover, when not binding to any
interface, we receive packets on both active and backup links. But when
binding to the master device, I only receive packets from the active
devices (which is the same behaviour than pre-4.12). When not binding to
any device and not using PACKET_ORIGDEV, one packet is said to be from
the master device and one packet is said to be from the backup device.
Previously, I had one packet from active device, one packet from backup
device and two packets from master device.

For me, this is a better situation than previously as we return to the
situation before 4.12 but you can get what you want by not binding to
any device _and_ using PACKET_ORIGDEV (otherwise, you are don't get the
right interface in all cases).

If it's unclear, I can provide more extensive results. I am using this
test program (comment the s.bind/s.setsockopt line if needed):

#v+
#!/usr/bin/env python3

import sys
import socket
import datetime

socket.SOL_PACKET = 263
socket.PACKET_ORIGDEV = 9

s = socket.socket(socket.AF_PACKET,
                  socket.SOCK_RAW,
                  socket.htons(0x88cc))
s.bind(("bond0", 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-
-- 
Localise input and output in subroutines.
            - The Elements of Programming Style (Kernighan & Plauger)