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

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Date:   Sat, 2 Feb 2019 00:00:36 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
        ast@...nel.org, netdev@...r.kernel.org, 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 10:47 PM, Jakub Kicinski wrote:
> On Fri, 1 Feb 2019 22:43:39 +0100, Daniel Borkmann wrote:
>> 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?
> 
> I haven't tested to be honest, but I think Maciek got that right -
> get_xdp_id_attr() should return IFLA_XDP_PROG_ID or a mode-specific
> attr based on flags.  And there is a check that only flag is set.
> 
> Or do you mean retrieving all program ids with one dump?

Yeah was thinking about the latter, but agree it's fine and probably
cleaner this way here.