linux-kernel - Re: [PATCH 08/10] bpf samples: Add utils.[ch] for using BPF

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Date:	Thu, 17 Dec 2015 15:11:39 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	ast@...nel.org, agartrell@...com, acme@...hat.com,
	bblanco@...mgrid.com, daniel@...earbox.net,
	daniel.wagner@...-carit.de, davem@...emloft.net, mingo@...nel.org,
	jolsa@...nel.org, xiakaixu@...wei.com, holzheu@...ux.vnet.ibm.com,
	yang.shi@...aro.org, linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [PATCH 08/10] bpf samples: Add utils.[ch] for using BPF

On Thu, Dec 17, 2015 at 05:23:12AM +0000, Wang Nan wrote:
> We are going to uses libbpf to replace old libbpf.[ch] and
> bpf_load.[ch]. This is the first patch of this work. In this patch,
> several macros and helpers in libbpf.[ch] and bpf_load.[ch] are
> merged into utils.[ch]. utils.[ch] utilizes libbpf in tools/lib to
> deal with BPF related things. They would be compiled after Makefile
> changes.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
...
> +#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
> +
> +static inline void * __must_check ERR_PTR(long error_)
> +{
> +	return (void *) error_;
> +}
> +
> +static inline long __must_check PTR_ERR(__force const void *ptr)
> +{
> +	return (long) ptr;
> +}
> +
> +static inline bool __must_check IS_ERR(__force const void *ptr)
> +{
> +	return IS_ERR_VALUE((unsigned long)ptr);
> +}

why copy paste this? I don't see the code that uses that.

> +	bpf_object__for_each_program(prog, obj) {
> +		const char *event = bpf_program__title(prog, false);
> +		int fd, err;
> +
> +		LIBBPF_PTR_ASSERT(event, goto errout);
> +		__LIBBPF_ASSERT(fd = bpf_program__nth_fd(prog, 0),
> +				>= 0,
> +				goto errout);
> +
> +		if (strncmp(event, "kprobe/", 7) == 0)
> +			err = create_kprobes(fd, event + 7, true);
> +		else if (strncmp(event, "kretprobe/", 10) == 0)
> +			err = create_kprobes(fd, event + 10, false);

I have a feeling that all bpf+socket, tcbpf1_kernc and trace_output_*.c
are broken, since I don't see a code that attaches programs to sockets
and to perf_event.
How did you test it?

> diff --git a/samples/bpf/utils.h b/samples/bpf/utils.h
> new file mode 100644
> index 0000000..5962a68
> --- /dev/null
> +++ b/samples/bpf/utils.h
> @@ -0,0 +1,217 @@
> +#ifndef __SAMPELS_UTILS_H
> +#define __SAMPELS_UTILS_H
> +
> +#include <bpf/libbpf.h>
> +#include <bpf/bpf.h>
> +
> +/* ALU ops on registers, bpf_add|sub|...: dst_reg += src_reg */
> +
> +#define BPF_ALU64_REG(OP, DST, SRC)				\
> +	((struct bpf_insn) {					\
> +		.code  = BPF_ALU64 | BPF_OP(OP) | BPF_X,	\
> +		.dst_reg = DST,					\
> +		.src_reg = SRC,					\
> +		.off   = 0,					\
> +		.imm   = 0 })

this probably belongs in tools/lib/bpf/bpf.h instead of samples.

The whole set depends on changes in perf/core tree, but
in net-next we have extra commit 30b50aa612018, so I don't see an easy way
to route this patch without creating across-tree merge conflicts during
merge window.
I'd suggest to apply all required work to tools/lib/bpf/ into perf/core
and leave samples/bpf/ after merge window.

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