Re: [PATCH bpf-next] bpf: Export rx queue info for reuseport ebpf prog

From: Yonghong Song
Date: Thu May 25 2023 - 01:26:54 EST

On 5/24/23 8:37 PM, Joe Damato wrote:
BPF_PROG_TYPE_SK_REUSEPORT / sk_reuseport ebpf programs do not have
access to the queue_mapping or napi_id of the incoming skb. Having
this information can help ebpf progs determine which listen socket to

This patch exposes both queue_mapping and napi_id so that
sk_reuseport ebpf programs can use this information to direct incoming
connections to the correct listen socket in the SOCKMAP.

For example:

A multi-threaded userland program with several threads accepting client
connections via a reuseport listen socket group might want to direct
incoming connections from specific receive queues (or NAPI IDs) to specific
listen sockets to maximize locality or for use with epoll busy-poll.

Signed-off-by: Joe Damato <jdamato@xxxxxxxxxx>
include/uapi/linux/bpf.h | 2 ++
net/core/filter.c | 10 ++++++++++
2 files changed, 12 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 9273c654743c..31560b506535 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6286,6 +6286,8 @@ struct sk_reuseport_md {
__u32 eth_protocol;
__u32 ip_protocol; /* IP protocol. e.g. IPPROTO_TCP, IPPROTO_UDP */
+ __u32 rx_queue_mapping; /* Rx queue associated with the skb */
+ __u32 napi_id; /* napi id associated with the skb */
__u32 bind_inany; /* Is sock bound to an INANY address? */
__u32 hash; /* A hash of the packet 4 tuples */

This won't work. You will need to append to the end of data structure
to keep it backward compatibility.

Also, recent kernel has a kfunc bpf_cast_to_kern_ctx() which converts
a ctx to a kernel ctx and you can then use tracing-coding-style to
access those fields. In this particular case, you can do

struct sk_reuseport_kern *kctx = bpf_cast_to_kern_ctx(ctx);

We have

struct sk_reuseport_kern {
struct sk_buff *skb;
struct sock *sk;
struct sock *selected_sk;
struct sock *migrating_sk;
void *data_end;
u32 hash;
u32 reuseport_id;
bool bind_inany;

through sk and skb pointer, you should be access the fields presented in
this patch. You can access more fields too.

So using bpf_cast_to_kern_ctx(), there is no need for more uapi changes.
Please give a try.

/* When reuse->migrating_sk is NULL, it is selecting a sk for the
diff --git a/net/core/filter.c b/net/core/filter.c
index 968139f4a1ac..71826e1ef7dc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -11134,6 +11134,8 @@ sk_reuseport_is_valid_access(int off, int size,
case bpf_ctx_range(struct sk_reuseport_md, ip_protocol):
case bpf_ctx_range(struct sk_reuseport_md, bind_inany):
case bpf_ctx_range(struct sk_reuseport_md, len):
+ case bpf_ctx_range(struct sk_reuseport_md, rx_queue_mapping):
+ case bpf_ctx_range(struct sk_reuseport_md, napi_id):
bpf_ctx_record_field_size(info, size_default);
return bpf_ctx_narrow_access_ok(off, size, size_default);
@@ -11183,6 +11185,14 @@ static u32 sk_reuseport_convert_ctx_access(enum bpf_access_type type,
+ case offsetof(struct sk_reuseport_md, rx_queue_mapping):
+ break;
+ case offsetof(struct sk_reuseport_md, napi_id):
+ break;
case offsetof(struct sk_reuseport_md, ip_protocol):