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 13:47:46 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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?