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

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Date:   Sat, 23 Nov 2019 17:59:08 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, magnus.karlsson@...il.com,
        magnus.karlsson@...el.com, jonathan.lemon@...il.com,
        ecree@...arflare.com, thoiland@...hat.com,
        andrii.nakryiko@...il.com, tariqt@...lanox.com,
        saeedm@...lanox.com, maximmi@...lanox.com
Subject: Re: [PATCH bpf-next v2 2/6] xdp: introduce xdp_call

On Sat, Nov 23, 2019 at 08:12:21AM +0100, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.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@...el.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; })

I cannot help but wonder whether it's possible to avoid copy-paste from
BPF_PROG_RUN().
At least could you place this new macro right next to BPF_PROG_RUN?
If it's in a different file eventually they may diverge.