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

From: Jiri Pirko <[email-masked]>
Date: Wed, 25 Oct 2023 17:47:05 +0200

Tue, Oct 24, 2023 at 11:48:58PM CEST, [email-masked] wrote:
>This work adds a new, minimal BPF-programmable device called "netkit"
>(former PoC code-name "meta") we recently presented at LSF/MM/BPF. The
>core idea is that BPF programs are executed within the drivers xmit routine
>and therefore e.g. in case of containers/Pods moving BPF processing closer
>to the source.
>
>One of the goals was that in case of Pod egress traffic, this allows to
>move BPF programs from hostns tcx ingress into the device itself, providing
>earlier drop or forward mechanisms, for example, if the BPF program
>determines that the skb must be sent out of the node, then a redirect to
>the physical device can take place directly without going through per-CPU
>backlog queue. This helps to shift processing for such traffic from softirq
>to process context, leading to better scheduling decisions/performance (see
>measurements in the slides).
>
>In this initial version, the netkit device ships as a pair, but we plan to
>extend this further so it can also operate in single device mode. The pair

Single device mode should work how?

>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)

>
>Additionally, the device can be operated in L3 (default) or L2 mode. The
>management of BPF programs is done via bpf_mprog, so that multi-attach is
>supported right from the beginning with similar API and dependency controls
>as tcx. For details on the latter see commit 053c8e1f235d ("bpf: Add generic
>attach/detach/query API for multi-progs"). tc BPF compatibility is provided,
>so that existing programs can be easily migrated.
>
>Going forward, we plan to use netkit devices in Cilium as the main device
>type for connecting Pods. They will be operated in L3 mode in order to
>simplify a Pod's neighbor management and the peer will operate in default
>drop mode, so that no traffic is leaving between the time when a Pod is
>brought up by the CNI plugin and programs attached by the agent.
>Additionally, the programs we attach via tcx on the physical devices are
>using bpf_redirect_peer() for inbound traffic into netkit device, hence the
>latter is also supporting the ndo_get_peer_dev callback. Similarly, we use
>bpf_redirect_neigh() for the way out, pushing from netkit peer to phys device
>directly. Also, BIG TCP is supported on netkit device. For the follow-up
>work in single device mode, we plan to convert Cilium's cilium_host/_net
>devices into a single one.
>
>An extensive test suite for checking device operations and the BPF program
>and link management API comes as BPF selftests in this series.
>

Couple of nitpicks below:

[..]

>+static int netkit_check_policy(int policy, struct nlattr *tb,
>+			       struct netlink_ext_ack *extack)
>+{
>+	switch (policy) {
>+	case NETKIT_PASS:
>+	case NETKIT_DROP:
>+		return 0;
>+	default:

Isn't this job for netlink policy?

>+		NL_SET_ERR_MSG_ATTR(extack, tb,
>+				    "Provided default xmit policy not supported");
>+		return -EINVAL;
>+	}
>+}
>+
>+static int netkit_check_mode(int mode, struct nlattr *tb,
>+			     struct netlink_ext_ack *extack)
>+{
>+	switch (mode) {
>+	case NETKIT_L2:
>+	case NETKIT_L3:
>+		return 0;
>+	default:

Isn't this job for netlink policy?

>+		NL_SET_ERR_MSG_ATTR(extack, tb,
>+				    "Provided device mode can only be L2 or L3");
>+		return -EINVAL;
>+	}
>+}
>+
>+static int netkit_validate(struct nlattr *tb[], struct nlattr *data[],
>+			   struct netlink_ext_ack *extack)
>+{
>+	struct nlattr *attr = tb[IFLA_ADDRESS];
>+
>+	if (!attr)
>+		return 0;
>+	NL_SET_ERR_MSG_ATTR(extack, attr,
>+			    "Setting Ethernet address is not supported");
>+	return -EOPNOTSUPP;
>+}
>+
>+static struct rtnl_link_ops netkit_link_ops;
>+
>+static int netkit_new_link(struct net *src_net, struct net_device *dev,
>+			   struct nlattr *tb[], struct nlattr *data[],
>+			   struct netlink_ext_ack *extack)
>+{
>+	struct nlattr *peer_tb[IFLA_MAX + 1], **tbp = tb, *attr;
>+	enum netkit_action default_prim = NETKIT_PASS;
>+	enum netkit_action default_peer = NETKIT_PASS;
>+	enum netkit_mode mode = NETKIT_L3;
>+	unsigned char ifname_assign_type;
>+	struct ifinfomsg *ifmp = NULL;
>+	struct net_device *peer;
>+	char ifname[IFNAMSIZ];
>+	struct netkit *nk;
>+	struct net *net;
>+	int err;
>+
>+	if (data) {
>+		if (data[IFLA_NETKIT_MODE]) {
>+			attr = data[IFLA_NETKIT_MODE];
>+			mode = nla_get_u32(attr);
>+			err = netkit_check_mode(mode, attr, extack);
>+			if (err < 0)
>+				return err;
>+		}
>+		if (data[IFLA_NETKIT_PEER_INFO]) {
>+			attr = data[IFLA_NETKIT_PEER_INFO];
>+			ifmp = nla_data(attr);
>+			err = rtnl_nla_parse_ifinfomsg(peer_tb, attr, extack);
>+			if (err < 0)
>+				return err;
>+			err = netkit_validate(peer_tb, NULL, extack);
>+			if (err < 0)
>+				return err;
>+			tbp = peer_tb;
>+		}
>+		if (data[IFLA_NETKIT_POLICY]) {
>+			attr = data[IFLA_NETKIT_POLICY];
>+			default_prim = nla_get_u32(attr);
>+			err = netkit_check_policy(default_prim, attr, extack);
>+			if (err < 0)
>+				return err;
>+		}
>+		if (data[IFLA_NETKIT_PEER_POLICY]) {
>+			attr = data[IFLA_NETKIT_PEER_POLICY];
>+			default_peer = nla_get_u32(attr);
>+			err = netkit_check_policy(default_peer, attr, extack);
>+			if (err < 0)
>+				return err;
>+		}
>+	}
>+
>+	if (ifmp && tbp[IFLA_IFNAME]) {
>+		nla_strscpy(ifname, tbp[IFLA_IFNAME], IFNAMSIZ);
>+		ifname_assign_type = NET_NAME_USER;
>+	} else {
>+		strscpy(ifname, "nk%d", IFNAMSIZ);
>+		ifname_assign_type = NET_NAME_ENUM;
>+	}
>+
>+	net = rtnl_link_get_net(src_net, tbp);
>+	if (IS_ERR(net))
>+		return PTR_ERR(net);
>+
>+	peer = rtnl_create_link(net, ifname, ifname_assign_type,
>+				&netkit_link_ops, tbp, extack);
>+	if (IS_ERR(peer)) {
>+		put_net(net);
>+		return PTR_ERR(peer);
>+	}
>+
>+	netif_inherit_tso_max(peer, dev);
>+
>+	if (mode == NETKIT_L2)
>+		eth_hw_addr_random(peer);
>+	if (ifmp && dev->ifindex)
>+		peer->ifindex = ifmp->ifi_index;
>+
>+	nk = netkit_priv(peer);
>+	nk->primary = false;
>+	nk->policy = default_peer;
>+	nk->mode = mode;
>+	bpf_mprog_bundle_init(&nk->bundle);
>+	RCU_INIT_POINTER(nk->active, NULL);
>+	RCU_INIT_POINTER(nk->peer, NULL);

Aren't these already 0?

>+
>+	err = register_netdevice(peer);
>+	put_net(net);
>+	if (err < 0)
>+		goto err_register_peer;
>+	netif_carrier_off(peer);
>+	if (mode == NETKIT_L2)
>+		dev_change_flags(peer, peer->flags & ~IFF_NOARP, NULL);
>+
>+	err = rtnl_configure_link(peer, NULL, 0, NULL);
>+	if (err < 0)
>+		goto err_configure_peer;
>+
>+	if (mode == NETKIT_L2)
>+		eth_hw_addr_random(dev);
>+	if (tb[IFLA_IFNAME])
>+		nla_strscpy(dev->name, tb[IFLA_IFNAME], IFNAMSIZ);
>+	else
>+		strscpy(dev->name, "nk%d", IFNAMSIZ);
>+
>+	nk = netkit_priv(dev);
>+	nk->primary = true;
>+	nk->policy = default_prim;
>+	nk->mode = mode;
>+	bpf_mprog_bundle_init(&nk->bundle);
>+	RCU_INIT_POINTER(nk->active, NULL);
>+	RCU_INIT_POINTER(nk->peer, NULL);
>+
>+	err = register_netdevice(dev);
>+	if (err < 0)
>+		goto err_configure_peer;
>+	netif_carrier_off(dev);
>+	if (mode == NETKIT_L2)
>+		dev_change_flags(dev, dev->flags & ~IFF_NOARP, NULL);
>+
>+	rcu_assign_pointer(netkit_priv(dev)->peer, peer);
>+	rcu_assign_pointer(netkit_priv(peer)->peer, dev);
>+	return 0;
>+err_configure_peer:
>+	unregister_netdevice(peer);
>+	return err;
>+err_register_peer:
>+	free_netdev(peer);
>+	return err;
>+}
>+

[..]