netdev - Re: [PATCH bpf-next v5 7/8] libbpf: Add a support for getting xdp prog id on ifindex

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Date:   Fri, 1 Feb 2019 22:43:39 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
        ast@...nel.org
Cc:     netdev@...r.kernel.org, jakub.kicinski@...ronome.com,
        brouer@...hat.com, john.fastabend@...il.com
Subject: Re: [PATCH bpf-next v5 7/8] libbpf: Add a support for getting xdp
 prog id on ifindex

On 02/01/2019 01:19 AM, Maciej Fijalkowski wrote:
> Since we have a dedicated netlink attributes for xdp setup on a
> particular interface, it is now possible to retrieve the program id that
> is currently attached to the interface. The use case is targeted for
> sample xdp programs, which will store the program id just after loading
> bpf program onto iface. On shutdown, the sample will make sure that it
> can unload the program by querying again the iface and verifying that
> both program id's matches.
> 
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
[...]
> +int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
> +{
> +	struct xdp_id_md xdp_id = {};
> +	int sock, ret;
> +	__u32 nl_pid;
> +	__u32 mask;
> +
> +	if (flags & ~XDP_FLAGS_MASK)
> +		return -EINVAL;
> +
> +	/* Check whether the single {HW,DRV,SKB} mode is set */
> +	flags &= (XDP_FLAGS_SKB_MODE | XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE);
> +	mask = flags - 1;
> +	if (flags && flags & mask)
> +		return -EINVAL;
> +
> +	sock = libbpf_netlink_open(&nl_pid);
> +	if (sock < 0)
> +		return sock;
> +
> +	xdp_id.ifindex = ifindex;
> +	xdp_id.flags = flags;
> +
> +	ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_id, &xdp_id);
> +	if (!ret)
> +		*prog_id = xdp_id.id;
> +
> +	close(sock);
> +	return ret;
> +}

Btw, is anyone going to follow-up on XDP_ATTACHED_MULTI support as well
later on?

Thanks,
Daniel