netdev - Re: [RFC net-next 08/18] tun: run offloaded XDP program in Tx path

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Date:   Sun, 1 Dec 2019 09:39:54 -0700
From:   David Ahern <dsahern@...il.com>
To:     Prashant Bhole <prashantbhole.linux@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        "Michael S . Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>, netdev@...r.kernel.org,
        qemu-devel@...gnu.org, kvm@...r.kernel.org
Subject: Re: [RFC net-next 08/18] tun: run offloaded XDP program in Tx path

On 11/26/19 4:07 AM, Prashant Bhole wrote:
> run offloaded XDP program as soon as packet is removed from the ptr
> ring. Since this is XDP in Tx path, the traditional handling of
> XDP actions XDP_TX/REDIRECT isn't valid. For this reason we call
> do_xdp_generic_core instead of do_xdp_generic. do_xdp_generic_core
> just runs the program and leaves the action handling to us.

What happens if an offloaded program returns XDP_REDIRECT?

Below you just drop the packet which is going to be a bad user
experience. A better user experience is to detect XDP return codes a
program uses, catch those that are not supported for this use case and
fail the install of the program.