[PATCH bpf-next v7 3/6] bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation
From: Nick Hudson <hidden>
Date: 2026-08-12 08:31:58
Also in:
bpf, lkml
Subsystem:
bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
Add new bpf_skb_adjust_room() decapsulation flags: - BPF_F_ADJ_ROOM_DECAP_L4_GRE - BPF_F_ADJ_ROOM_DECAP_L4_UDP - BPF_F_ADJ_ROOM_DECAP_IPXIP4 - BPF_F_ADJ_ROOM_DECAP_IPXIP6 These flags let BPF programs describe which tunnel layer is being removed, so later changes can update tunnel-related GSO state accordingly during decapsulation. This patch only introduces the UAPI flag definitions and helper documentation. Co-developed-by: Max Tottenham <redacted> Signed-off-by: Max Tottenham <redacted> Co-developed-by: Anna Glasgall <redacted> Signed-off-by: Anna Glasgall <redacted> Signed-off-by: Nick Hudson <redacted> Reviewed-by: Willem de Bruijn <willemb@google.com> --- include/uapi/linux/bpf.h | 34 ++++++++++++++++++++++++++++++++-- tools/include/uapi/linux/bpf.h | 34 ++++++++++++++++++++++++++++++++-- 2 files changed, 64 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f6c9dc856858..732b35cc08d1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h@@ -3038,8 +3038,34 @@ union bpf_attr { * * * **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**, * **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**: - * Indicate the new IP header version after decapsulating the outer - * IP header. Used when the inner and outer IP versions are different. + * Indicate the new IP header version after decapsulating the + * outer IP header. Used when the inner and outer IP versions + * are different. These flags only trigger a protocol change + * without clearing any tunnel-specific GSO flags. + * + * * **BPF_F_ADJ_ROOM_DECAP_L4_GRE**: + * Clear GRE tunnel GSO flags (SKB_GSO_GRE and SKB_GSO_GRE_CSUM) + * when decapsulating a GRE tunnel. + * + * * **BPF_F_ADJ_ROOM_DECAP_L4_UDP**: + * Clear UDP tunnel GSO flags (SKB_GSO_UDP_TUNNEL and + * SKB_GSO_UDP_TUNNEL_CSUM) when decapsulating a UDP tunnel. + * + * * **BPF_F_ADJ_ROOM_DECAP_IPXIP4**: + * Clear IPIP/SIT tunnel GSO flag (SKB_GSO_IPXIP4) when decapsulating + * a tunnel with an outer IPv4 header (IPv4-in-IPv4 or IPv6-in-IPv4). + * + * * **BPF_F_ADJ_ROOM_DECAP_IPXIP6**: + * Clear IPv6 encapsulation tunnel GSO flag (SKB_GSO_IPXIP6) when + * decapsulating a tunnel with an outer IPv6 header (IPv6-in-IPv6 + * or IPv4-in-IPv6). + * + * When using the decapsulation flags above, the skb->encapsulation + * flag is automatically cleared if all tunnel-specific GSO flags + * (SKB_GSO_UDP_TUNNEL, SKB_GSO_UDP_TUNNEL_CSUM, SKB_GSO_GRE, + * SKB_GSO_GRE_CSUM, SKB_GSO_IPXIP4, SKB_GSO_IPXIP6) have been + * removed from the packet. This handles cases where all tunnel + * layers have been decapsulated. * * A call to this helper is susceptible to change the underlying * packet buffer. Therefore, at load time, all checks on pointers
@@ -6293,6 +6319,10 @@ enum bpf_adj_room_flags { BPF_F_ADJ_ROOM_ENCAP_L2_ETH = (1ULL << 6), BPF_F_ADJ_ROOM_DECAP_L3_IPV4 = (1ULL << 7), BPF_F_ADJ_ROOM_DECAP_L3_IPV6 = (1ULL << 8), + BPF_F_ADJ_ROOM_DECAP_L4_GRE = (1ULL << 9), + BPF_F_ADJ_ROOM_DECAP_L4_UDP = (1ULL << 10), + BPF_F_ADJ_ROOM_DECAP_IPXIP4 = (1ULL << 11), + BPF_F_ADJ_ROOM_DECAP_IPXIP6 = (1ULL << 12), }; enum {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index f6c9dc856858..732b35cc08d1 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h@@ -3038,8 +3038,34 @@ union bpf_attr { * * * **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**, * **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**: - * Indicate the new IP header version after decapsulating the outer - * IP header. Used when the inner and outer IP versions are different. + * Indicate the new IP header version after decapsulating the + * outer IP header. Used when the inner and outer IP versions + * are different. These flags only trigger a protocol change + * without clearing any tunnel-specific GSO flags. + * + * * **BPF_F_ADJ_ROOM_DECAP_L4_GRE**: + * Clear GRE tunnel GSO flags (SKB_GSO_GRE and SKB_GSO_GRE_CSUM) + * when decapsulating a GRE tunnel. + * + * * **BPF_F_ADJ_ROOM_DECAP_L4_UDP**: + * Clear UDP tunnel GSO flags (SKB_GSO_UDP_TUNNEL and + * SKB_GSO_UDP_TUNNEL_CSUM) when decapsulating a UDP tunnel. + * + * * **BPF_F_ADJ_ROOM_DECAP_IPXIP4**: + * Clear IPIP/SIT tunnel GSO flag (SKB_GSO_IPXIP4) when decapsulating + * a tunnel with an outer IPv4 header (IPv4-in-IPv4 or IPv6-in-IPv4). + * + * * **BPF_F_ADJ_ROOM_DECAP_IPXIP6**: + * Clear IPv6 encapsulation tunnel GSO flag (SKB_GSO_IPXIP6) when + * decapsulating a tunnel with an outer IPv6 header (IPv6-in-IPv6 + * or IPv4-in-IPv6). + * + * When using the decapsulation flags above, the skb->encapsulation + * flag is automatically cleared if all tunnel-specific GSO flags + * (SKB_GSO_UDP_TUNNEL, SKB_GSO_UDP_TUNNEL_CSUM, SKB_GSO_GRE, + * SKB_GSO_GRE_CSUM, SKB_GSO_IPXIP4, SKB_GSO_IPXIP6) have been + * removed from the packet. This handles cases where all tunnel + * layers have been decapsulated. * * A call to this helper is susceptible to change the underlying * packet buffer. Therefore, at load time, all checks on pointers
@@ -6293,6 +6319,10 @@ enum bpf_adj_room_flags { BPF_F_ADJ_ROOM_ENCAP_L2_ETH = (1ULL << 6), BPF_F_ADJ_ROOM_DECAP_L3_IPV4 = (1ULL << 7), BPF_F_ADJ_ROOM_DECAP_L3_IPV6 = (1ULL << 8), + BPF_F_ADJ_ROOM_DECAP_L4_GRE = (1ULL << 9), + BPF_F_ADJ_ROOM_DECAP_L4_UDP = (1ULL << 10), + BPF_F_ADJ_ROOM_DECAP_IPXIP4 = (1ULL << 11), + BPF_F_ADJ_ROOM_DECAP_IPXIP6 = (1ULL << 12), }; enum {
--
2.34.1