On 06/16/2016 04:50 PM, Hannes Frederic Sowa wrote:
On 16.06.2016 16:37, Daniel Borkmann wrote:
On 06/16/2016 03:57 PM, Derek Ditch wrote:
[...]
Begin forwarded message:
From: bugzilla-dae...@bugzilla.kernel.org
Subject: [Bug 120441] af_packet no longer uses symmetric hashing
Date: June 16, 2016 at 07:35:54 -0500
To: derek.di...@gmail.com
https://bugzilla.kernel.org/show_bug.cgi?id=120441
Just thinking out loud, perhaps one way would be to implement your own
fanout
hashing via eBPF demuxer, f.e. in case CPU selection etc wouldn't work.
Another
option could be to have a (2nd) customizable hash demux that would
enforce to
always go through the flow-dissector and where you would have a socket
option
to control keys for it, but I presume that seems rather less desirable.
Isn't a symmetric hashing for af-packet something very fundamental?
Looks much more like a bug to me.
I agree it would be useful resp. fundamental. I'm not quite sure whether
PACKET_FANOUT_HASH always had this guarantee since the initial implementation
f.e. depending on whether the skb got fanout demuxed from RX or TX paths,
you would either use a hw hash or it would have gone through the kernel's
(predecessor) flow dissector (and therefore potentially to different packet
sockets eventually). It might be the case that this got noticed due to the
flow dissector nowadays collecting more input for building its hash, hmm.
Bye,
Hannes
