netdev - Re: [PATCH][RESEND] bonding: delete migrated IP addresses from the rlb hash table

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Date:	Thu, 29 Nov 2012 13:10:07 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Jiri Bohac <jbohac@...e.cz>
cc:	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH][RESEND] bonding: delete migrated IP addresses from the rlb hash table

Jiri Bohac <jbohac@...e.cz> wrote:

>Bonding in balance-alb mode records information from ARP packets
>passing through the bond in a hash table (rx_hashtbl).
>
>At certain situations (e.g. link change of a slave),
>rlb_update_rx_clients() will send out ARP packets to update ARP
>caches of other hosts on the network to achieve RX load
>balancing.
>
>The problem is that once an IP address is recorded in the hash
>table, it stays there indefinitely. If this IP address is
>migrated to a different host in the network, bonding still sends
>out ARP packets that poison other systems' ARP caches with
>invalid information.
>
>This patch solves this by looking at all incoming ARP packets,
>and checking if the source IP address is one of the source
>addresses stored in the rx_hashtbl. If it is, but the MAC
>addresses differ, the corresponding hash table entries are
>removed. Thus, when an IP address is migrated, the first ARP
>broadcast by its new owner will purge the offending entries of
>rx_hashtbl.
>
>The hash table is hashed by ip_dst. To be able to do the above
>check efficiently (not walking the whole hash table), we need a
>reverse mapping (by ip_src).
>
>I added three new members in struct rlb_client_info:
>   rx_hashtbl[x].src_first will point to the start of a list of
>      entries for which hash(ip_src) == x.
>   The list is linked with src_next and src_prev.
>
>When an incoming ARP packet arrives at rlb_arp_recv()
>rlb_purge_src_ip() can quickly walk only the entries on the
>corresponding lists, i.e. the entries that are likely to contain
>the offending IP address.
>
>To avoid confusion, I renamed these existing fields of struct 
>rlb_client_info:
>	next -> used_next
>	prev -> used_prev
>	rx_hashtbl_head -> rx_hashtbl_used_head
>
>(The current linked list is _not_ a list of hash table
>entries with colliding ip_dst. It's a list of entries that are
>being used; its purpose is to avoid walking the whole hash table
>when looking for used entries.)
>
>Signed-off-by: Jiri Bohac <jbohac@...e.cz>

Signed-off-by: Jay Vosburgh <fubar@...ibm.com>

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com

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