Re: [1/1 take 2] Unified socket storage. (with small bench).

[David Miller <davem@davemloft.net>]

From: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Date: Wed, 9 May 2007 13:34:43 +0400

> On Tue, May 08, 2007 at 11:48:28PM -0700, David Miller (davem@davemloft.net) wrote:
> > One thing that will need to be adjust for current tree is the UDP
> > hashing mechanism.  But as far as I can tell your code should be able
> > to handle the new scheme (we now hash UDP by saddr+port when
> > possible, and this reminds me that IPV6 is broken and needs some
> > repairs).
> 
> Yes, udp with multicast can be a problem, but it can be solved exactly
> the same way I implemented netlink broadcast (simple solution) -
> multicast sockets are placed into own list/hash table/trie with special
> bit in key/whatever and accessed when needed.

Actually, I am not talking about multicast. :)

In 2.6.22 what happens now in UDP is that if a non-wildcard rcv_saddr
is specified, we try to hash using the rcv_saddr and the port.  But
when binding we have to check first if an existing port+wildcard bind
exists.

See __udp_lib_get_port() in Linus's current tree.

> > What exactly does the 'stages' arg mean?  Is this a method to handle
> > partially bound sockets?
> 
> It is a fallback to select a listening socket, which has remote
> addr/port as zero, so when socket it selected from tree, lookup wants to
> first get established socket with given remote identity and if this
> fails, it tries to select a wildcard one.

This kind of logic also has implications for UDP. :-)