Re: [PATCH v2 bpf-next 2/2] selftests: bpf: Add a new test for bare tracepoints

On 01/16/21 18:11, Yonghong Song wrote:

On 1/16/21 10:21 AM, Qais Yousef wrote:

quoted

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 <redacted>
---
  .../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?

I don't think so. The structure should still remain RO AFAIU.

quoted

-	.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?

I don't see what difference this makes.

quoted

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

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

We already set err=-errno. So shouldn't we return negative too?

quoted

+
+	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;
	}

I kept the code consistent with the definition of trigger_module_test_read().

I'll leave it up to the maintainer to pick up the style changes if they prefer
it this way.

Thanks for the ack and for the review.

Cheers

--
Qais Yousef