bpf: make it easier to add new metadata kfunc

No functional changes.

Instead of having hand-crafted code in bpf_dev_bound_resolve_kfunc,
move kfunc <> xmo handler relationship into XDP_METADATA_KFUNC_xxx.
This way, any time new kfunc is added, we don't have to touch
bpf_dev_bound_resolve_kfunc.

Also document XDP_METADATA_KFUNC_xxx arguments since we now have
more than two and it might be confusing what is what.

Cc: netdev@vger.kernel.org
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230913171350.369987-2-sdf@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

include/net/xdp.h

@@ -383,14 +383,22 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
 
 #define DEV_MAP_BULK_SIZE XDP_BULK_QUEUE_SIZE
 
+/* Define the relationship between xdp-rx-metadata kfunc and
+ * various other entities:
+ * - xdp_rx_metadata enum
+ * - kfunc name
+ * - xdp_metadata_ops field
+ */
 #define XDP_METADATA_KFUNC_xxx	\
 	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_TIMESTAMP, \
-			   bpf_xdp_metadata_rx_timestamp) \
+			   bpf_xdp_metadata_rx_timestamp, \
+			   xmo_rx_timestamp) \
 	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_HASH, \
-			   bpf_xdp_metadata_rx_hash) \
+			   bpf_xdp_metadata_rx_hash, \
+			   xmo_rx_hash) \
 
-enum {
-#define XDP_METADATA_KFUNC(name, _) name,
+enum xdp_rx_metadata {
+#define XDP_METADATA_KFUNC(name, _, __) name,
 XDP_METADATA_KFUNC_xxx
 #undef XDP_METADATA_KFUNC
 MAX_XDP_METADATA_KFUNC,

kernel/bpf/offload.c

@@ -845,10 +845,11 @@ void *bpf_dev_bound_resolve_kfunc(struct bpf_prog *prog, u32 func_id)
 	if (!ops)
 		goto out;
 
-	if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP))
-		p = ops->xmo_rx_timestamp;
-	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_HASH))
-		p = ops->xmo_rx_hash;
+#define XDP_METADATA_KFUNC(name, _, xmo) \
+	if (func_id == bpf_xdp_metadata_kfunc_id(name)) p = ops->xmo;
+	XDP_METADATA_KFUNC_xxx
+#undef XDP_METADATA_KFUNC
+
 out:
 	up_read(&bpf_devs_lock);
 

net/core/xdp.c

@@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
 __diag_pop();
 
 BTF_SET8_START(xdp_metadata_kfunc_ids)
-#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
+#define XDP_METADATA_KFUNC(_, name, __) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
 XDP_METADATA_KFUNC_xxx
 #undef XDP_METADATA_KFUNC
 BTF_SET8_END(xdp_metadata_kfunc_ids)
@@ -752,7 +752,7 @@ static const struct btf_kfunc_id_set xdp_metadata_kfunc_set = {
 };
 
 BTF_ID_LIST(xdp_metadata_kfunc_ids_unsorted)
-#define XDP_METADATA_KFUNC(name, str) BTF_ID(func, str)
+#define XDP_METADATA_KFUNC(name, str, _) BTF_ID(func, str)
 XDP_METADATA_KFUNC_xxx
 #undef XDP_METADATA_KFUNC