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Message-ID: <fdda7117-e823-e240-4735-617a3df8a0cc@fb.com>
Date: Mon, 18 Jan 2021 09:48:53 -0800
From: Yonghong Song <yhs@...com>
To: Qais Yousef <qais.yousef@....com>
CC: <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
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 1/18/21 4:18 AM, Qais Yousef wrote:
> On 01/16/21 18:11, Yonghong Song wrote:
>>
>>
>> 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?
>
> I don't think so. The structure should still remain RO AFAIU.
okay.
>
>>
>>> - .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.
>
>>
>>> + 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?
Oh, yes, return -ENOMEM sounds right here.
>
>>
>>> +
>>> + 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)) {
Here it should be ... "failed: %d\n", -errno.
>> err = -errno;
>> goto out;
>> }
>
> I kept the code consistent with the definition of trigger_module_test_read().
The original patch code:
+static int trigger_module_test_write(int write_sz)
+{
+ int fd, err;
+ char *buf = malloc(write_sz);
+
+ if (!buf)
+ 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;
+
+ write(fd, buf, write_sz);
+ close(fd);
+out:
+ free(buf);
+
+ return 0;
+}
Even for "fd < 0" case, it "goto out" and "return 0". We should return
error code here instead of 0.
Second, "err = -errno" is set before checking fd < 0. If fd >= 0, err
might inherit an postive errno from previous failure.
In trigger_module_test_write(), it is okay since the err is only used
when fd < 0:
err = -errno;
if (CHECK(fd < 0, "testmod_file_open", "failed: %d\n", err))
return err;
My above rewrite intends to use "err" during final "return" statement,
so I put assignment of "err = -errno" inside the CHECK branch.
But there are different ways to implement this properly.
>
> 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.
No problem.
>
> Cheers
>
> --
> Qais Yousef
>
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