On Tue, 13 Dec 2016 01:12:32 +0100 (CET) Michał Mirosław <mirq-li...@rere.qmqm.pl> wrote:
> Dear NetDevs > > This series removes an abuse of VLAN CFI bit in Linux networking stack. > Currently Linux always clears the bit on outgoing traffic and presents > it cleared to userspace (even via AF_PACKET/tcpdump when hw-accelerated). > > This uses a new vlan_present bit in struct skbuff, and removes an assumption > that vlan_proto != 0 when VLAN tag is present. > > As I can't test most of the driver changes, please look at them carefully. > > The series is supposed to be bisect-friendly and that requires temporary > insertion of #define VLAN_TAG_PRESENT in BPF code to be able to split > JIT changes per architecture. > > Best Regards, > Michał Mirosław I wonder if CFI can every validly be non-zero in the modern world, on Hyper-V. There are no token ring devices and that seems to be the only use case where CFI would be non-zero. Unless someone is planning to reuse it a a protocol bit which seems like a really bad idea. Maybe the right thing is to keep hard coded as zero and not start adding more untestable code conditions. My recommendation would be get rid of VLAN_TAG_PRESENT, but don't preserve CFI bit.
