On Fri, Sep 17, 2021 at 6:56 PM Hou Tao [off-list ref] wrote:

Add a writable bare tracepoint in bpf_testmod module, and
trigger its calling when reading /sys/kernel/bpf_testmod
with a specific buffer length. The reading will return
the value in writable context if the early return flag
is enabled in writable context.

Signed-off-by: Hou Tao <redacted>
---
 .../bpf/bpf_testmod/bpf_testmod-events.h      | 15 ++++++++
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 10 ++++++
 .../selftests/bpf/bpf_testmod/bpf_testmod.h   |  5 +++
 .../selftests/bpf/prog_tests/module_attach.c  | 36 +++++++++++++++++++
 .../selftests/bpf/progs/test_module_attach.c  | 14 ++++++++
 5 files changed, 80 insertions(+)

[...]

+static int trigger_module_test_writable(int *val)
+{
+       int fd, err;
+       char buf[65];
+       ssize_t rd;
+
+       fd = open("/sys/kernel/bpf_testmod", O_RDONLY);
+       err = -errno;
+       if (CHECK(fd < 0, "testmod_file_open", "failed: %d\n", err))
+               return err;
+
+       rd = read(fd, buf, sizeof(buf) - 1);
+       err = rd < 0 ? -errno : -ENODATA;
+       if (CHECK(rd <= 0, "testmod_file_rd_val", "failed: rd %zd errno %d\n",
+                 rd, errno)) {
+               close(fd);
+               return err;
+       }
+

please use ASSERT_xxx() consistently

+       buf[rd] = '\0';
+       *val = strtol(buf, NULL, 0);
+       close(fd);
+
+       return 0;
+}
+

[...]