On Mon, 2015-09-28 at 20:04 -0700, Tom Herbert wrote: > > > I've been pondering a bit of a redesign in this space. I think the > > skb struct should be explicit in its instructions to hardware for > > which offloads to do for each packet. > > > > In this way, the stack would be *directly* telling the drivers what to > > do (and what not to do), solving all sorts of bugs and really improving > > driver reliability and implementation. > > > Doesn't CHECKSUM_PARTIAL with csum_offset and csum_start already tell > the driver unambiguously what to do wrt checksum offload?
Right. That's precisely what we *do* have. But as things stand, we
can't *use* it to its full capability.
It's fine for decent devices which can handle such explicit
instructions (advertised by the NETIF_F_HW_CSUM feature).
The problem is the crappy devices that can *only* checksum UDP and TCP
frames, advertised with the NETIF_F_IP{V6,}_CSUM features. We make a
primitive attempt *not* to feed arbitrary checksum requests to such
hardware. But we fail — we end up feeding *all* Legacy IP packets to a
NETIF_F_IP_CSUM device, and *all* IPv6 packets to a NETIF_F_IPV6_CSUM
device, regardless of whether they're *actually* TCP or UDP packets.
That's the problem I'm trying to solve. And then we *can* make full use
of the generic checksum offload (I had it working for ICMPv6 at one
point: http://lists.openwall.net/netdev/2013/01/14/38 ).
--
David Woodhouse Open Source Technology Centre
david.woodho...@intel.com Intel Corporation
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