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

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Message-ID: <20191201163730-mutt-send-email-mst@kernel.org>
Date:   Sun, 1 Dec 2019 16:40:22 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     dsahern@...il.com, prashantbhole.linux@...il.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

On Sun, Dec 01, 2019 at 12:56:21PM -0800, David Miller wrote:
> 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.

Right. But it is helpful to expose the supported functionality
to guest in some way, if nothing else then so that
guests can be moved between different hosts.

Also, we need a way to report this kind of event to guest
so it's possible to figure out what went wrong.

-- 
MST