[PATCH bpf-next v2 2/6] xdp: introduce xdp_call

["Björn Töpel" <bjorn.topel@gmail.com>]

From: Björn Töpel <bjorn.topel@intel.com>

The xdp_call.h header wraps a more user-friendly API around the BPF
dispatcher. A user adds a trampoline/XDP caller using the
DEFINE_XDP_CALL macro, and updates the BPF dispatcher via
xdp_call_update(). The actual dispatch is done via xdp_call().

Note that xdp_call() is only supported for builtin drivers. Module
builds will fallback to bpf_prog_run_xdp().

The next patch will show-case how the i40e driver uses xdp_call.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 include/linux/xdp_call.h | 66 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 include/linux/xdp_call.h

diff --git a/include/linux/xdp_call.h b/include/linux/xdp_call.h
new file mode 100644
index 000000000000..69b2d325a787
--- /dev/null
+++ b/include/linux/xdp_call.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright(c) 2019 Intel Corporation. */
+#ifndef _LINUX_XDP_CALL_H
+#define _LINUX_XDP_CALL_H
+
+#include <linux/filter.h>
+
+#if defined(CONFIG_BPF_JIT) && defined(CONFIG_RETPOLINE) && !defined(MODULE)
+
+void bpf_dispatcher_change_prog(void *func, struct bpf_prog *from,
+				struct bpf_prog *to);
+
+#define XDP_CALL_TRAMP(name)	____xdp_call_##name##_tramp
+
+#define DEFINE_XDP_CALL(name)						\
+	unsigned int XDP_CALL_TRAMP(name)(				\
+		const void *xdp_ctx,					\
+		const struct bpf_insn *insnsi,				\
+		unsigned int (*bpf_func)(const void *,			\
+					 const struct bpf_insn *))	\
+	{								\
+		return bpf_func(xdp_ctx, insnsi);			\
+	}
+
+#define DECLARE_XDP_CALL(name)						\
+	unsigned int XDP_CALL_TRAMP(name)(				\
+		const void *xdp_ctx,					\
+		const struct bpf_insn *insnsi,				\
+		unsigned int (*bpf_func)(const void *,			\
+					 const struct bpf_insn *))
+
+#define xdp_call_run(name, prog, ctx) ({				\
+	u32 ret;							\
+	cant_sleep();							\
+	if (static_branch_unlikely(&bpf_stats_enabled_key)) {		\
+		struct bpf_prog_stats *stats;				\
+		u64 start = sched_clock();				\
+		ret = XDP_CALL_TRAMP(name)(ctx,				\
+					   (prog)->insnsi,		\
+					   (prog)->bpf_func);		\
+		stats = this_cpu_ptr((prog)->aux->stats);		\
+		u64_stats_update_begin(&stats->syncp);			\
+		stats->cnt++;						\
+		stats->nsecs += sched_clock() - start;			\
+		u64_stats_update_end(&stats->syncp);			\
+	} else {							\
+		ret = XDP_CALL_TRAMP(name)(ctx,				\
+					   (prog)->insnsi,		\
+					   (prog)->bpf_func);		\
+	}								\
+	ret; })
+
+#define xdp_call_update(name, from_xdp_prog, to_xdp_prog)	\
+	bpf_dispatcher_change_prog(&XDP_CALL_TRAMP(name),	\
+				   from_xdp_prog,		\
+				   to_xdp_prog)
+
+#else
+
+#define DEFINE_XDP_CALL(name)
+#define DECLARE_XDP_CALL(name)
+#define xdp_call_run(name, xdp_prog, xdp) bpf_prog_run_xdp(xdp_prog, xdp)
+#define xdp_call_update(name, from_xdp_prog, to_xdp_prog)
+
+#endif
+#endif /* _LINUX_XDP_CALL_H */
-- 
2.20.1