On Mon, Apr 8, 2019 at 12:59 PM Alan Maguire alan.maguire@oracle.com wrote:
commit 868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags") introduced support to bpf_skb_adjust_room for GSO-friendly GRE and UDP encapsulation.
For GSO to work for skbs, the inner headers (mac and network) need to be marked. For L3 encapsulation using bpf_skb_adjust_room, the mac and network headers are identical. Here we provide a way of specifying the inner mac header length for cases where L2 encap is desired. Such an approach can support encapsulated ethernet headers, MPLS headers etc. For example to convert from a packet of form [eth][ip][tcp] to [eth][ip][udp][inner mac][ip][tcp], something like the following could be done:
headroom = sizeof(iph) + sizeof(struct udphdr) + inner_maclen; ret = bpf_skb_adjust_room(skb, headroom, BPF_ADJ_ROOM_MAC, BPF_F_ADJ_ROOM_ENCAP_L4_UDP | BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 | BPF_F_ADJ_ROOM_ENCAP_L2(inner_maclen));Signed-off-by: Alan Maguire alan.maguire@oracle.com
static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff, u64 flags) {
u16 mac_len = 0, inner_mac = 0, inner_net = 0, inner_trans = 0; bool encap = flags & BPF_F_ADJ_ROOM_ENCAP_L3_MASK;
u16 mac_len = 0, inner_net = 0, inner_trans = 0; unsigned int gso_type = SKB_GSO_DODGY;
u8 inner_mac_len = flags >> BPF_ADJ_ROOM_ENCAP_L2_SHIFT; int ret; if (skb_is_gso(skb) && !skb_is_gso_tcp(skb)) {@@ -3008,6 +3011,9 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
mac_len = skb->network_header - skb->mac_header; inner_net = skb->network_header;
if (inner_mac_len > len_diff)return -EINVAL;inner_mac = inner_net - inner_mac_len;
nit: variable inner_mac is not needed.
@@ -3031,7 +3036,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff, gso_type |= SKB_GSO_GRE; else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV6) gso_type |= SKB_GSO_IPXIP6;
else
else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV4) gso_type |= SKB_GSO_IPXIP4;
Nice catch. L2 encap should also work without L3 encap.