netdev - Re: [PATCH bpf-next v4 1/7] netkit, bpf: Add bpf programmable net device

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Date: Thu, 26 Oct 2023 07:18:11 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, martin.lau@...ux.dev,
	razor@...ckwall.org, ast@...nel.org, andrii@...nel.org,
	john.fastabend@...il.com, sdf@...gle.com, toke@...nel.org,
	kuba@...nel.org, andrew@...n.ch,
	Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next v4 1/7] netkit, bpf: Add bpf programmable net
 device

Wed, Oct 25, 2023 at 07:20:01PM CEST, daniel@...earbox.net wrote:
>On 10/25/23 5:47 PM, Jiri Pirko wrote:
>> Tue, Oct 24, 2023 at 11:48:58PM CEST, daniel@...earbox.net wrote:
>[...]
>> > comes with a primary and a peer device. Only the primary device, typically
>> > residing in hostns, can manage BPF programs for itself and its peer. The
>> > peer device is designated for containers/Pods and cannot attach/detach
>> > BPF programs. Upon the device creation, the user can set the default policy
>> > to 'pass' or 'drop' for the case when no BPF program is attached.
>> 
>> It looks to me that you only need the host (primary) netdevice to be
>> used as a handle to attach the bpf programs. Because the bpf program
>> can (and probably in real use case will) redirect to uplink/another
>> pod netdevice skipping the host (primary) netdevice, correct?
>> 
>> If so, why can't you do just single device mode from start finding a
>> different sort of bpf attach handle? (not sure which)
>
>The first point where we switch netns from a K8s Pod is out of the netdevice.
>For the CNI case the vast majority has one but there could also be multi-
>homing for Pods where there may be two or more, and from a troubleshooting
>PoV aka tcpdump et al, it is the most natural point. Other attach handle
>inside the Pod doesn't really fit given from policy PoV it also must be
>unreachable for apps inside the Pod itself.

Okay. What is the usecase for the single device model then?

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