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

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Message-Id: <20191201.125621.1568040486743628333.davem@davemloft.net>
Date:   Sun, 01 Dec 2019 12:56:21 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     dsahern@...il.com
Cc:     prashantbhole.linux@...il.com, mst@...hat.com, jasowang@...hat.com,
        ast@...nel.org, daniel@...earbox.net, jakub.kicinski@...ronome.com,
        hawk@...nel.org, john.fastabend@...il.com, kafai@...com,
        songliubraving@...com, yhs@...com, 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

From: David Ahern <dsahern@...il.com>
Date: Sun, 1 Dec 2019 09:39:54 -0700

> 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.

This is not universally possible.

Return codes can be calculated dynamically, come from maps potentially
shared with other bpf programs, etc.

So unfortunately this suggestion is not tenable.