linux-kernel - Re: [PATCH v1 3/3] kunit: fix bug of extra newline characters in debugfs logs

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Message-ID: <CABVgOSngiZZ6HTAOTriB=TveYOPoZVChqyeNfaBsDzFCY+_A2A@mail.gmail.com>
Date:   Thu, 9 Feb 2023 13:06:17 +0800
From:   David Gow <davidgow@...gle.com>
To:     Rae Moar <rmoar@...gle.com>
Cc:     brendanhiggins@...gle.com, dlatypov@...gle.com,
        skhan@...uxfoundation.org, kunit-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v1 3/3] kunit: fix bug of extra newline characters in
 debugfs logs

On Wed, 1 Feb 2023 at 06:04, Rae Moar <rmoar@...gle.com> wrote:
>
> Fix bug of the extra newline characters in debugfs logs. When a
> line is added to debugfs with a newline character at the end,
> an extra line appears in the debugfs log. Remove these extra lines.
>
> Add kunit_log_newline_test to provide test coverage for this issue.
> (Also, move kunit_log_test above suite definition to remove the
> unnecessary declaration prior to the suite definition)
>
> Signed-off-by: Rae Moar <rmoar@...gle.com>
> ---

I've got some reservations about this patch.

Firstly, could we have an example of the problem in the commit
message, so we know what we're fixing?

Secondly, I _really_ don't like the way this just removes newlines
from log lines if there are too many. It feels like a hack, rather
than a proper fix.

I suspect the actual issue here is in the kunit_log macro in
include/kunit/test.h:
https://elixir.bootlin.com/linux/latest/source/include/kunit/test.h#L417

kunit_log_append((test_or_suite)->log, fmt "\n", ##__VA_ARGS__); \

The "\n" concatenated here is probably the issue. The printk statement
doesn't add a newline, but that's because printk implicitly does if
KERN_CONT is not added.

So maybe the correct fix here is to use:
printk(KERN_CONT lvl fmt "\n", ##__VA_ARGS__)

That'd add the newline, rather than get rid of it, but at least should
make the behaviour more similar between printk and the debugfs log.
Equally, you could use KERN_CONT and get rid of the "\n" in both
places, requiring it in log messages.

Thirdly, I don't really like the way the test is skipped if debugfs
isn't active. Could we skip it if test->log is not valid instead or
using a compile-time #ifdef?

I do like the move of kunit_log_test though. That definitely cleans things up!

Cheers,
-- David


>  lib/kunit/kunit-test.c | 36 ++++++++++++++++++++++++------------
>  lib/kunit/test.c       |  9 ++++++++-
>  2 files changed, 32 insertions(+), 13 deletions(-)
>
> diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
> index 4df0335d0d06..e9114a466f1e 100644
> --- a/lib/kunit/kunit-test.c
> +++ b/lib/kunit/kunit-test.c
> @@ -443,18 +443,6 @@ static struct kunit_suite kunit_resource_test_suite = {
>         .test_cases = kunit_resource_test_cases,
>  };
>
> -static void kunit_log_test(struct kunit *test);
> -
> -static struct kunit_case kunit_log_test_cases[] = {
> -       KUNIT_CASE(kunit_log_test),
> -       {}
> -};
> -
> -static struct kunit_suite kunit_log_test_suite = {
> -       .name = "kunit-log-test",
> -       .test_cases = kunit_log_test_cases,
> -};
> -
>  static void kunit_log_test(struct kunit *test)
>  {
>         struct kunit_suite suite;
> @@ -481,6 +469,30 @@ static void kunit_log_test(struct kunit *test)
>  #endif
>  }
>
> +static void kunit_log_newline_test(struct kunit *test)
> +{
> +#ifdef CONFIG_KUNIT_DEBUGFS
> +       kunit_info(test, "extra newline\n");
> +
> +       KUNIT_ASSERT_NOT_NULL_MSG(test, strstr(test->log, "extra newline\n"),
> +               "Missing log line, full log:\n%s", test->log);
> +       KUNIT_EXPECT_NULL(test, strstr(test->log, "extra newline\n\n"));
> +#else
> +       kunit_skip(test, "only useful when debugfs is enabled");
> +#endif
> +}
> +
> +static struct kunit_case kunit_log_test_cases[] = {
> +       KUNIT_CASE(kunit_log_test),
> +       KUNIT_CASE(kunit_log_newline_test),
> +       {}
> +};
> +
> +static struct kunit_suite kunit_log_test_suite = {
> +       .name = "kunit-log-test",
> +       .test_cases = kunit_log_test_cases,
> +};
> +
>  static void kunit_status_set_failure_test(struct kunit *test)
>  {
>         struct kunit fake;
> diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> index 27763f0b420c..76d9c31943bf 100644
> --- a/lib/kunit/test.c
> +++ b/lib/kunit/test.c
> @@ -117,6 +117,7 @@ void kunit_log_append(char *log, const char *fmt, ...)
>         char line[KUNIT_LOG_SIZE];
>         va_list args;
>         int len_left;
> +       int line_len;
>
>         if (!log)
>                 return;
> @@ -125,10 +126,16 @@ void kunit_log_append(char *log, const char *fmt, ...)
>         if (len_left <= 0)
>                 return;
>
> +       // Evaluate the length of the line with arguments
>         va_start(args, fmt);
> -       vsnprintf(line, sizeof(line), fmt, args);
> +       line_len = vsnprintf(line, sizeof(line), fmt, args);
>         va_end(args);
>
> +       // If line has two newline characters, do not print
> +       // second newline character
> +       if (fmt[strlen(fmt) - 2] == '\n')
> +               line[line_len - 1] = '\0';
> +
>         strncat(log, line, len_left);
>  }
>  EXPORT_SYMBOL_GPL(kunit_log_append);
> --
> 2.39.1.456.gfc5497dd1b-goog
>

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