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Date:   Sat, 16 Jan 2021 18:11:50 -0800
From:   Yonghong Song <yhs@...com>
To:     Qais Yousef <qais.yousef@....com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests: bpf: Add a new test for bare
 tracepoints



On 1/16/21 10:21 AM, Qais Yousef wrote:
> Reuse module_attach infrastructure to add a new bare tracepoint to check
> we can attach to it as a raw tracepoint.
> 
> Signed-off-by: Qais Yousef <qais.yousef@....com>
> ---
>   .../bpf/bpf_testmod/bpf_testmod-events.h      |  6 +++++
>   .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 21 ++++++++++++++-
>   .../selftests/bpf/bpf_testmod/bpf_testmod.h   |  6 +++++
>   .../selftests/bpf/prog_tests/module_attach.c  | 27 +++++++++++++++++++
>   .../selftests/bpf/progs/test_module_attach.c  | 10 +++++++
>   5 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> index b83ea448bc79..89c6d58e5dd6 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> @@ -28,6 +28,12 @@ TRACE_EVENT(bpf_testmod_test_read,
>   		  __entry->pid, __entry->comm, __entry->off, __entry->len)
>   );
>   
> +/* A bare tracepoint with no event associated with it */
> +DECLARE_TRACE(bpf_testmod_test_write_bare,
> +	TP_PROTO(struct task_struct *task, struct bpf_testmod_test_write_ctx *ctx),
> +	TP_ARGS(task, ctx)
> +);
> +
>   #endif /* _BPF_TESTMOD_EVENTS_H */
>   
>   #undef TRACE_INCLUDE_PATH
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 2df19d73ca49..e900adad2276 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -28,9 +28,28 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
>   EXPORT_SYMBOL(bpf_testmod_test_read);
>   ALLOW_ERROR_INJECTION(bpf_testmod_test_read, ERRNO);
>   
> +noinline ssize_t
> +bpf_testmod_test_write(struct file *file, struct kobject *kobj,
> +		      struct bin_attribute *bin_attr,
> +		      char *buf, loff_t off, size_t len)
> +{
> +	struct bpf_testmod_test_write_ctx ctx = {
> +		.buf = buf,
> +		.off = off,
> +		.len = len,
> +	};
> +
> +	trace_bpf_testmod_test_write_bare(current, &ctx);
> +
> +	return -EIO; /* always fail */
> +}
> +EXPORT_SYMBOL(bpf_testmod_test_write);
> +ALLOW_ERROR_INJECTION(bpf_testmod_test_write, ERRNO);
> +
>   static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {

Do we need to remove __ro_after_init?

> -	.attr = { .name = "bpf_testmod", .mode = 0444, },
> +	.attr = { .name = "bpf_testmod", .mode = 0666, },
>   	.read = bpf_testmod_test_read,
> +	.write = bpf_testmod_test_write,
>   };
>   
>   static int bpf_testmod_init(void)
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
> index b81adfedb4f6..b3892dc40111 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
> @@ -11,4 +11,10 @@ struct bpf_testmod_test_read_ctx {
>   	size_t len;
>   };
>   
> +struct bpf_testmod_test_write_ctx {
> +	char *buf;
> +	loff_t off;
> +	size_t len;
> +};
> +
>   #endif /* _BPF_TESTMOD_H */
> diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> index 50796b651f72..e4605c0b5af1 100644
> --- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
> +++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c
> @@ -21,9 +21,34 @@ static int trigger_module_test_read(int read_sz)
>   	return 0;
>   }
>   
> +static int trigger_module_test_write(int write_sz)
> +{
> +	int fd, err;

Init err = 0?

> +	char *buf = malloc(write_sz);
> +
> +	if (!buf)
> +		return -ENOMEM;

Looks like we already non-negative value, so return ENOMEM?

> +
> +	memset(buf, 'a', write_sz);
> +	buf[write_sz-1] = '\0';
> +
> +	fd = open("/sys/kernel/bpf_testmod", O_WRONLY);
> +	err = -errno;
> +	if (CHECK(fd < 0, "testmod_file_open", "failed: %d\n", err))
> +		goto out;

Change the above to
	fd = open("/sys/kernel/bpf_testmod", O_WRONLY);
	if (CHECK(fd < 0, "testmod_file_open", "failed: %d\n", errno)) {
		err = -errno;
		goto out;
	}

> +
> +	write(fd, buf, write_sz);
> +	close(fd);
> +out:
> +	free(buf);
> +

No need for extra line here.

> +	return 0;

return err.

> +}
> +
>   void test_module_attach(void)
>   {
>   	const int READ_SZ = 456;
> +	const int WRITE_SZ = 457;
>   	struct test_module_attach* skel;
>   	struct test_module_attach__bss *bss;
>   	int err;
> @@ -48,8 +73,10 @@ void test_module_attach(void)
>   
>   	/* trigger tracepoint */
>   	ASSERT_OK(trigger_module_test_read(READ_SZ), "trigger_read");
> +	ASSERT_OK(trigger_module_test_write(WRITE_SZ), "trigger_write");
>   
>   	ASSERT_EQ(bss->raw_tp_read_sz, READ_SZ, "raw_tp");
> +	ASSERT_EQ(bss->raw_tp_bare_write_sz, WRITE_SZ, "raw_tp_bare");
>   	ASSERT_EQ(bss->tp_btf_read_sz, READ_SZ, "tp_btf");
>   	ASSERT_EQ(bss->fentry_read_sz, READ_SZ, "fentry");
>   	ASSERT_EQ(bss->fentry_manual_read_sz, READ_SZ, "fentry_manual");
> diff --git a/tools/testing/selftests/bpf/progs/test_module_attach.c b/tools/testing/selftests/bpf/progs/test_module_attach.c
> index efd1e287ac17..bd37ceec5587 100644
> --- a/tools/testing/selftests/bpf/progs/test_module_attach.c
> +++ b/tools/testing/selftests/bpf/progs/test_module_attach.c
> @@ -17,6 +17,16 @@ int BPF_PROG(handle_raw_tp,
>   	return 0;
>   }
>   
> +__u32 raw_tp_bare_write_sz = 0;
> +
> +SEC("raw_tp/bpf_testmod_test_write_bare")
> +int BPF_PROG(handle_raw_tp_bare,
> +	     struct task_struct *task, struct bpf_testmod_test_write_ctx *write_ctx)
> +{
> +	raw_tp_bare_write_sz = BPF_CORE_READ(write_ctx, len);
> +	return 0;
> +}
> +
>   __u32 tp_btf_read_sz = 0;
>   
>   SEC("tp_btf/bpf_testmod_test_read")
> 

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