On Mon, 2015-10-05 at 09:23 -0700, Tom Herbert wrote: > > 1) Drivers may advertise NETIF_F_HW_CSUM. The stack will indicate > checksum offload exclusively using the > CHECKSUM_PARTIAL/csum_start/csum_offset interface. No additional > interfaces (bits in skbuff should not be needed) > 2) A driver may inspect packets via ndo_check to decide if it wants to > offload the checksum, if not cancels NETIF_F_HW_CSUM in the packet. > 3) In driver xmit when CHECKSUM_PARTIAL is set the driver MUST > correctly resolve the checksum-- either by properly offloading to the > device or calling skb_checksum_help.
In cases where they haven't used .ndo_features_check() to ensure that they don't *see* such packets, sure. But using .ndo_features_check() should probably be the preferred method. > 4) To help drivers for devices with limited offload capabilities we'll > define a helper function to check for typical restrictions (.e.g. IPv4 > only, TCP/UDP only. no encapsulation, no IPv6 extension headers, > etc.). I am working on this helper function and will send RFC shortly. I do suspect that helper function would benefit from seeing TCP/UDP flags in the high bits of csum_offset, rather than grubbing around in the packet for itself to see if it's really TCP/UDP. After all, it's almost free to set those in the first place — at least for locally -generated packets. And not *so* hard to add them in skb_partial_csum_set(). But hey, if you can push an implementation which is grubbing around in the packet then at least *I* don't have to feel dirty for it... :) -- David Woodhouse Open Source Technology Centre david.woodho...@intel.com Intel Corporation
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