Subject: Re: [RFC PATCH 08/12] bpf: add devmap, a map for storing net device references

From: Jesper Dangaard Brouer <[email-masked]>
Date: Sat, 8 Jul 2017 20:57:50 +0200

On Fri, 07 Jul 2017 10:37:12 -0700
John Fastabend <[email-masked]> wrote:

> Device map (devmap) is a BPF map, primarily useful for networking
> applications, that uses a key to lookup a reference to a netdevice.
> 
> The map provides a clean way for BPF programs to build virtual port
> to physical port maps. Additionally, it provides a scoping function
> for the redirect action itself allowing multiple optimizations. Future
> patches will leverage the map to provide batching at the XDP layer.
> 
> Another optimization/feature, that is not yet implemented, would be
> to support multiple netdevices per key to support efficient multicast
> and broadcast support.

[...]

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 74ea96e..06073ba 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1294,6 +1294,14 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
>  		    func_id != BPF_FUNC_current_task_under_cgroup)
>  			goto error;
>  		break;
> +	/* devmap returns a pointer to a live net_device ifindex that we cannot
> +	 * allow to be modified from bpf side. So do not allow lookup elemnts
                                                                      ^^^^^^^
Spelling of elements

> +	 * for now.
> +	 */
> +	case BPF_MAP_TYPE_DEVMAP:
> +		if (func_id == BPF_FUNC_map_lookup_elem)
> +			goto error;
> +		break;

Reviewer notice this limitation from the bpf_prog side.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer