Re: AF_PACKET mmap() v4...

[Eric Dumazet <eric.dumazet@gmail.com>]

On Thu, 2015-11-05 at 10:39 +0100, Daniel Borkmann wrote:
> On 11/05/2015 10:07 AM, Arnd Bergmann wrote:
> > On Thursday 05 November 2015 00:04:14 David Miller wrote:
> >> As part of fixing y2038 problems, Arnd is going to have to make a new
> >> version fo the AF_PACKET mmap() tpacker descriptors in order to extend
> >> the time values to 64-bit.
> >>
> >> So I want everyone to think about whether there are any other changes
> >> we might want to make given that we have to make a v4 anyways.
> >>
> >> Particularly, I am rather certain that the buffer management could be
> >> improved.  Some have complained that v3 is kinda awkward to use and/or
> >> suboptimal is various ways.
> >
> > I have taken a closer look at the actual timestamp data now, and noticed
> > that we use __u32 for both tp_sec and ts_sec in the user visible data.
> > This means that once we fix the internal implementation to use 64-bit
> > timestamps, we actually won't overflow until 2106 because the 2038 overflow
> > is only for signed 32-bit numbers as we have in 'struct timespec'.
> >
> > So the good news is that we can keep the existing v1 through v3 formats
> > beyond 2038, but only as long as all user space that cares about the
> > value also interprets it as unsigned.
> 
> Right, I was just about to ask that. So we could just make a union in
> AF_PACKET's UAPI for a single 64-bit variable (as in ktime_t) to fix that.

If I am not mistaken, af_packet also lacks the ability to properly set
skb->protocol

I noticed this using trafgen on a bonding device, when I did my SYNFLOOD
tests for TCP listener rewrite.

The bonding hash function might uses flow dissector, but as this flow
dissection depends on skb->protocol, all the traffic is directed on a
single slave.