Re: AF_XDP socket TX path interact with TC?

[Jun Hu <hujun.work@gmail.com>]

On Tue, Oct 26, 2021 at 4:08 AM Konrad Zemek <konrad@zemek.io> wrote:
>
> On Monday, October 25th, 2021 at 8:26 PM, Jun Hu <hujun.work@gmail.com> wrote:
>
> > On Mon, Oct 25, 2021 at 3:48 AM Toke Høiland-Jørgensen toke@redhat.com wrote:
> >
> > > Jun Hu hujun.work@gmail.com writes:
> > >
> > > > Hi,
> > > >
> > > > I want to put a timestamp in the egress packets, and I want to use
> > > >
> > > > AF_XDP socket for both sending and receiving packets; since a XDP
> > > >
> > > > kernel program only work in ingress direction, I wonder if I could use
> > > >
> > > > a tc kernel program to change a packet sent out via an AF_XDP socket?
> > > >
> > > > I searched around, but couldn't find any direct answer...
> > >
> > > Nope, AF_XDP bypasses the stack completely, so TC won't see the packet
> > >
> > > on egress...
> > >
> > > -Toke
> >
> > Ok, thanks for the clarification, I guess I have to wait for the XDP
> >
> > egress support ...
>
> You can also directly modify the packet that you send out through an AF_XDP socket, before putting it on the outgoing queue. Is there anything specific that you would want to do in an egress-attached BPF program that you would not be able to do in the userspace program that manages your AF_XDP socket?
>
> Konrad

Yes, that's what I am doing right now, however ideally I want to add a
timestamp to the packet as close as it egress the NIC; since AF_XDP
doesn't have access to hardware timestamp, that's why I was searching
for an alternative solution.