[PATCH 2/8] of: Enable DTB loading on UML for KUnit tests

[Stephen Boyd]

To fully exercise common clk framework code in KUnit we need to
associate 'struct device' pointers with 'struct device_node' pointers so
that things like clk_get() can parse DT nodes for 'clocks' and so that
clk providers can use DT to provide clks; the most common mode of
operation for clk providers.

Adding support to KUnit so that it loads a DTB is fairly simple after
commit b31297f04e86 ("um: Add devicetree support"). We can simply pass a
pre-compiled deviectree blob (DTB) on the kunit.py commandline and UML
will load it. The problem is that tests won't know that the commandline
has been modified, nor that a DTB has been loaded. Take a different
approach so that tests can skip if a DTB hasn't been loaded.

Reuse the Makefile logic from the OF unittests to build a DTB into the
kernel. This DTB will be for the mythical machine "linux,kunit", i.e.
the devicetree for the KUnit "board". In practice, it is a dtsi file
that will gather includes for kunit tests that rely in part on a
devicetree being loaded. The devicetree should only be loaded if
CONFIG_OF_KUNIT=y. Make that a choice config parallel to the existing
CONFIG_OF_UNITTEST so that only one devicetree can be loaded in the
system at a time. Similarly, the kernel commandline option to load a
DTB is ignored if CONFIG_OF_KUNIT is enabled so that only one DTB is
loaded at a time.

Add a simple unit test to confirm that the DTB loading worked. Future
tests will add to the kunit.dtsi file to include their specific test
nodes.

Cc: Richard Weinberger <ric...@nod.at>
Cc: Anton Ivanov <anton....@cambridgegreys.com>
Cc: Johannes Berg <joha...@sipsolutions.net>
Cc: Vincent Whitchurch <vincent.w...@axis.com>
Cc: Rob Herring <rob...@kernel.org>
Cc: Frank Rowand <frowan...@gmail.com>
Signed-off-by: Stephen Boyd <sb...@kernel.org>
---
arch/um/kernel/dtb.c | 29 +++++++++++++++--
drivers/of/Kconfig | 26 ++++++++++++++++
drivers/of/Makefile | 1 +
drivers/of/kunit/.kunitconfig | 4 +++
drivers/of/kunit/Makefile | 4 +++
drivers/of/kunit/kunit.dtsi | 8 +++++
drivers/of/kunit/kunit.dtso | 4 +++
drivers/of/kunit/uml_dtb_test.c | 55 +++++++++++++++++++++++++++++++++
8 files changed, 128 insertions(+), 3 deletions(-)
create mode 100644 drivers/of/kunit/.kunitconfig
create mode 100644 drivers/of/kunit/Makefile
create mode 100644 drivers/of/kunit/kunit.dtsi
create mode 100644 drivers/of/kunit/kunit.dtso
create mode 100644 drivers/of/kunit/uml_dtb_test.c

diff --git a/arch/um/kernel/dtb.c b/arch/um/kernel/dtb.c
index 484141b06938..ee63951b12df 100644
--- a/arch/um/kernel/dtb.c
+++ b/arch/um/kernel/dtb.c
@@ -15,9 +15,32 @@ void uml_dtb_init(void)
long long size;
void *area;

- area = uml_load_file(dtb, &size);
- if (!area)
- return;
+ if (IS_ENABLED(CONFIG_OF_KUNIT)) {
+ /*
+ * __dtbo_kunit_begin[] and __dtbo_kunit_end[] are magically
+ * created by cmd_dt_S_dtbo in scripts/Makefile.lib from the
+ * drivers/of/kunit/kunit.dtsi file.
+ */
+ extern uint8_t __dtbo_kunit_begin[];
+ extern uint8_t __dtbo_kunit_end[];
+
+ size = __dtbo_kunit_end - __dtbo_kunit_begin;
+ if (!size) {
+ pr_warn("%s: kunit testcases is empty\n", __func__);
+ return;
+ }
+
+ /* creating copy */
+ area = memblock_alloc(size, 8);
+ if (!area)
+ return;
+
+ memcpy(area, __dtbo_kunit_begin, size);
+ } else {
+ area = uml_load_file(dtb, &size);
+ if (!area)
+ return;
+ }

if (!early_init_dt_scan(area)) {
pr_err("invalid DTB %s\n", dtb);
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 80b5fd44ab1c..1f968b6a3dde 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -12,6 +12,20 @@ menuconfig OF

if OF

+choice
+ prompt "Devicetree Runtime Tests"
+ default OF_UNITTEST
+
+config OF_KUNIT
+ bool "Devicetree KUnit support" if KUNIT
+ depends on UML
+ select IRQ_DOMAIN
+ select OF_EARLY_FLATTREE
+ help
+ This option builds in KUnit test cases that rely on device tree infrastructure.
+ A fake Device Tree Blob (DTB) is loaded on the UML kernel running KUnit so that
+ KUnit tests can test device tree dependent code.
+
config OF_UNITTEST
bool "Device Tree runtime unit tests"
depends on !SPARC
@@ -25,6 +39,18 @@ config OF_UNITTEST

If unsure, say N here, but this option is safe to enable.

+endchoice
+
+config OF_DTB_KUNIT_TEST
+ tristate "Devicetree KUnit DTB Test" if !KUNIT_ALL_TESTS
+ depends on KUNIT
+ default KUNIT_ALL_TESTS
+ help
+ This option builds unit tests for the "linux,kunit" DTB built into
+ the UML kernel image.
+
+ If unsure, say N here, but this option is safe to enable.
+
config OF_ALL_DTBS
bool "Build all Device Tree Blobs"
depends on COMPILE_TEST
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index e0360a44306e..16eef3fdf60a 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -19,4 +19,5 @@ obj-y += kexec.o
endif
endif

+obj-y += kunit/
obj-$(CONFIG_OF_UNITTEST) += unittest-data/
diff --git a/drivers/of/kunit/.kunitconfig b/drivers/of/kunit/.kunitconfig
new file mode 100644
index 000000000000..1def0ad30d29
--- /dev/null
+++ b/drivers/of/kunit/.kunitconfig
@@ -0,0 +1,4 @@
+CONFIG_KUNIT=y
+CONFIG_OF=y
+CONFIG_OF_KUNIT=y
+CONFIG_OF_DTB_KUNIT_TEST=y
diff --git a/drivers/of/kunit/Makefile b/drivers/of/kunit/Makefile
new file mode 100644
index 000000000000..ffe0447e1ac7
--- /dev/null
+++ b/drivers/of/kunit/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_OF_KUNIT) += kunit.dtbo.o
+
+obj-$(CONFIG_OF_DTB_KUNIT_TEST) += uml_dtb_test.o
diff --git a/drivers/of/kunit/kunit.dtsi b/drivers/of/kunit/kunit.dtsi
new file mode 100644
index 000000000000..82f6c3e2b8d5
--- /dev/null
+++ b/drivers/of/kunit/kunit.dtsi
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/ {
+ model = "KUnit UML";
+ compatible = "linux,kunit";
+};
+
+/* Include testcase dtsi files below */
diff --git a/drivers/of/kunit/kunit.dtso b/drivers/of/kunit/kunit.dtso
new file mode 100644
index 000000000000..50187e8d1422
--- /dev/null
+++ b/drivers/of/kunit/kunit.dtso
@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
+/dts-v1/;
+
+#include "kunit.dtsi"
diff --git a/drivers/of/kunit/uml_dtb_test.c b/drivers/of/kunit/uml_dtb_test.c
new file mode 100644
index 000000000000..8966c9ebf51f
--- /dev/null
+++ b/drivers/of/kunit/uml_dtb_test.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for DTB loading on UML
+ */
+#include <linux/kconfig.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+
+#include <kunit/test.h>
+
+/*
+ * Test that of_machine_is_compatible() returns positive int when loaded DTB
+ * matches.
+ */
+static void uml_dtb_of_machine_compatible_test(struct kunit *test)
+{
+ KUNIT_EXPECT_GT(test, of_machine_is_compatible("linux,kunit"), 0);
+}
+
+/*
+ * Test that of_flat_dt_get_machine_name() returns the expected 'model' from the
+ * loaded DTB.
+ */
+static void uml_dtb_of_flat_dt_get_machine_name_test(struct kunit *test)
+{
+ KUNIT_EXPECT_STREQ(test, of_flat_dt_get_machine_name(), "KUnit UML");
+}
+
+static struct kunit_case uml_dtb_test_cases[] = {
+ KUNIT_CASE(uml_dtb_of_machine_compatible_test),
+ KUNIT_CASE(uml_dtb_of_flat_dt_get_machine_name_test),
+ {}
+};
+
+static int uml_dtb_test_init(struct kunit *test)
+{
+ if (!IS_ENABLED(CONFIG_OF_KUNIT))
+ kunit_skip(test, "requires CONFIG_OF_KUNIT");
+
+ return 0;
+}
+
+/*
+ * Test suite to confirm DTB is loaded on UML.
+ */
+static struct kunit_suite uml_dtb_suite = {
+ .name = "uml_dtb",
+ .init = uml_dtb_test_init,
+ .test_cases = uml_dtb_test_cases,
+};
+
+kunit_test_suites(
+ &uml_dtb_suite,
+);
+MODULE_LICENSE("GPL");
--
https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git/
https://git.kernel.org/pub/scm/linux/kernel/git/sboyd/spmi.git

[David Gow]

On Thu, 2 Mar 2023 at 09:38, Stephen Boyd <sb...@kernel.org> wrote:
>
> To fully exercise common clk framework code in KUnit we need to
> associate 'struct device' pointers with 'struct device_node' pointers so
> that things like clk_get() can parse DT nodes for 'clocks' and so that
> clk providers can use DT to provide clks; the most common mode of
> operation for clk providers.
>
> Adding support to KUnit so that it loads a DTB is fairly simple after
> commit b31297f04e86 ("um: Add devicetree support"). We can simply pass a
> pre-compiled deviectree blob (DTB) on the kunit.py commandline and UML
> will load it. The problem is that tests won't know that the commandline
> has been modified, nor that a DTB has been loaded. Take a different
> approach so that tests can skip if a DTB hasn't been loaded.
>
> Reuse the Makefile logic from the OF unittests to build a DTB into the
> kernel. This DTB will be for the mythical machine "linux,kunit", i.e.
> the devicetree for the KUnit "board". In practice, it is a dtsi file
> that will gather includes for kunit tests that rely in part on a
> devicetree being loaded. The devicetree should only be loaded if
> CONFIG_OF_KUNIT=y. Make that a choice config parallel to the existing
> CONFIG_OF_UNITTEST so that only one devicetree can be loaded in the
> system at a time. Similarly, the kernel commandline option to load a
> DTB is ignored if CONFIG_OF_KUNIT is enabled so that only one DTB is
> loaded at a time.

This feels a little bit like it's just papering over the real problem,
which is that there's no way tests can skip themselves if no DTB is
loaded.

That being said, I do think that there's probably some sense in
supporting the compiled-in DTB as well (it's definitely simpler than
patching kunit.py to always pass the extra command-line option in, for
example).
But maybe it'd be nice to have the command-line option override the
built-in one if present.

I think this should probably override the KUnit dtb if present (so,
try to load the dtb, and fallback to the builtin one). If not, I think
we should at least print a warning if a DTB is specified on the
command-line, but we're not using it.

> --
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[Rob Herring]

No. This needs to be reworked such that a kernel rebuild is not needed
to run different tests. I suspect that the overlay approach will do that
for you.

> + prompt "Devicetree Runtime Tests"
> + default OF_UNITTEST
> +
> +config OF_KUNIT
> + bool "Devicetree KUnit support" if KUNIT
> + depends on UML

This is not a great dependency either...

Rob

[Stephen Boyd]

Quoting David Gow (2023-03-02 23:15:04)

Hmm. I think you're suggesting that the unit test data be loaded
whenever CONFIG_OF=y and CONFIG_KUNIT=y. Then tests can check for
CONFIG_OF and skip if it isn't enabled?

>
> That being said, I do think that there's probably some sense in
> supporting the compiled-in DTB as well (it's definitely simpler than
> patching kunit.py to always pass the extra command-line option in, for
> example).
> But maybe it'd be nice to have the command-line option override the
> built-in one if present.

Got it. I need to test loading another DTB on the commandline still, but
I think this won't be a problem. We'll load the unittest-data DTB even
with KUnit on UML, so assuming that works on UML right now it should be
unchanged by this series once I resend.

[David Gow]

More of the opposite: that we should have some way of supporting tests
which might want to use a DTB other than the built-in one. Mostly for
non-UML situations where an actual devicetree is needed to even boot
far enough to get test output (so we wouldn't be able to override it
with a compiled-in test one).

I think moving to overlays probably will render this idea obsolete:
but the thought was to give test code a way to check for the required
devicetree nodes at runtime, and skip the test if they weren't found.
That way, the failure mode for trying to boot this on something which
required another device tree for, e.g., serial, would be "these tests
are skipped because the wrong device tree is loaded", not "I get no
output because serial isn't working".

Again, though, it's only really needed for non-UML, and just loading
overlays as needed should be much more sensible anyway.

> >
> > That being said, I do think that there's probably some sense in
> > supporting the compiled-in DTB as well (it's definitely simpler than
> > patching kunit.py to always pass the extra command-line option in, for
> > example).
> > But maybe it'd be nice to have the command-line option override the
> > built-in one if present.
>
> Got it. I need to test loading another DTB on the commandline still, but
> I think this won't be a problem. We'll load the unittest-data DTB even
> with KUnit on UML, so assuming that works on UML right now it should be
> unchanged by this series once I resend.

Again, moving to overlays should render this mostly obsolete, no? Or
am I misunderstanding how the overlay stuff will work?

One possible future advantage of being able to test with custom DTs at
boot time would be for fuzzing (provide random DT properties, see what
happens in the test). We've got some vague plans to support a way of
passing custom data to tests to support this kind of case (though, if
we're using overlays, maybe the test could just patch those if we
wanted to do that).


Cheers,
-- David

[Stephen Boyd]

Quoting David Gow (2023-03-10 00:09:48)

> On Fri, 10 Mar 2023 at 07:19, Stephen Boyd <sb...@kernel.org> wrote:
> >
> >
> > Hmm. I think you're suggesting that the unit test data be loaded
> > whenever CONFIG_OF=y and CONFIG_KUNIT=y. Then tests can check for
> > CONFIG_OF and skip if it isn't enabled?
> >
>
> More of the opposite: that we should have some way of supporting tests
> which might want to use a DTB other than the built-in one. Mostly for
> non-UML situations where an actual devicetree is needed to even boot
> far enough to get test output (so we wouldn't be able to override it
> with a compiled-in test one).

Ok, got it.

>
> I think moving to overlays probably will render this idea obsolete:
> but the thought was to give test code a way to check for the required
> devicetree nodes at runtime, and skip the test if they weren't found.
> That way, the failure mode for trying to boot this on something which
> required another device tree for, e.g., serial, would be "these tests
> are skipped because the wrong device tree is loaded", not "I get no
> output because serial isn't working".
>
> Again, though, it's only really needed for non-UML, and just loading
> overlays as needed should be much more sensible anyway.

I still have one niggle here. Loading overlays requires
CONFIG_OF_OVERLAY, and the overlay loading API returns -ENOTSUPP when
CONFIG_OF_OVERLAY=n. For now I'm checking for the config being enabled
in each test, but I'm thinking it may be better to simply call
kunit_skip() from the overlay loading function if the config is
disabled. This way tests can simply call the overlay loading function
and we'll halt the test immediately if the config isn't enabled.

>
> > >
> > > That being said, I do think that there's probably some sense in
> > > supporting the compiled-in DTB as well (it's definitely simpler than
> > > patching kunit.py to always pass the extra command-line option in, for
> > > example).
> > > But maybe it'd be nice to have the command-line option override the
> > > built-in one if present.
> >
> > Got it. I need to test loading another DTB on the commandline still, but
> > I think this won't be a problem. We'll load the unittest-data DTB even
> > with KUnit on UML, so assuming that works on UML right now it should be
> > unchanged by this series once I resend.
>
> Again, moving to overlays should render this mostly obsolete, no? Or
> am I misunderstanding how the overlay stuff will work?

Right, overlays make it largely a moot issue. The way the OF unit tests
work today is by grafting a DTB onto the live tree. I'm reusing that
logic to graft a container node target for kunit tests to add their
overlays too. It will be clearer once I post v2.

>
> One possible future advantage of being able to test with custom DTs at
> boot time would be for fuzzing (provide random DT properties, see what
> happens in the test). We've got some vague plans to support a way of
> passing custom data to tests to support this kind of case (though, if
> we're using overlays, maybe the test could just patch those if we
> wanted to do that).

Ah ok. I can see someone making a fuzzer that modifies devicetree
properties randomly, e.g. using different strings for clock-names.

This reminds me of another issue I ran into. I wanted to test adding the
same platform device to the platform bus twice to confirm that the
second device can't be added. That prints a warning, which makes
kunit.py think that the test has failed because it printed a warning. Is
there some way to avoid that? I want something like

KUNIT_EXPECT_WARNING(test, <call some function>)

so I can test error cases.

[David Gow]

That sounds sensible, though there is a potential pitfall. If
kunit_skip() is called directly from overlay code, might introduce a
dependency on kunit.ko from the DT overlay, which we might not want.
The solution there is either to have a kunit wrapper function (so the
call is already in kunit.ko), or to have a hook to skip the current
test (which probably makes sense to do anyway, but I think the wrapper
is the better option).

Hmm... I'd've thought that shouldn't be a problem: kunit.py should
ignore most messages during a test, unless it can't find a valid
result line. What does the raw KTAP output look like? (You can get it
from kunit.py by passing the --raw_output option).

That being said, a KUNIT_EXPECT_LOG_MESSAGE() or similar is something
we've wanted for a while. I think that the KASAN folks have been
working on something similar using console tracepoints:
https://lore.kernel.org/all/ebf96ea600050f00ed567e80505ae8f24...@google.com/

Cheers,
-- David

[Frank Rowand]

DT unittests already have a similar concept. A test can report that a
kernel warning (or any other specific text) either (1) must occur for the
test to pass or (2) must _not_ occur for the test to pass. The check
for the kernel warning is done by the test output parsing program
scripts/dtc/of_unittest_expect.

The reporting by a test of an expected error in drivers/of/unittest.c
is done by EXPECT_BEGIN() and EXPECT_END(). These have been in
unittest for a long time.

The reporting by a test of a not expected to occur error is done
by EXPECT_NOT_BEGIN() and EXPECT_NOT_END(). These are added to
unittest in linux 6.3-rc1.

I discussed this concept in one of the early TAP / KTAP discussion
threads and expect to start a discussion thread on this specific
topic in the KTAP Specification V2 context. I expect the discussion
to result in a different implementation than what DT unittests are
using (bike shedding likely to ensue) but whatever is agreed to
should be easy for DT to switch to.

[Frank Rowand]

The link to the early KTAP discussion on this concept is:

https://lore.kernel.org/all/d38bf9f9-8a39-87a6...@gmail.com/T/#u

> threads and expect to start a discussion thread on this specific
> topic in the KTAP Specification V2 context. I expect the discussion
> to result in a different implementation than what DT unittests are
> using (bike shedding likely to ensue) but whatever is agreed to
> should be easy for DT to switch to.

The link to the KTAP Specification Version 2 process and progress is:

https://elinux.org/Test_Results_Format_Notes#KTAP_version_2

-Frank

[David Gow]

Thanks -- I'd totally forgotten about that!

I still personally would prefer a way of checking this from within the
kernel, as if we're just printing out "EXPECT: " lines, then it's not
possible to know if a test passes just from the raw results (and
things like statistics can't be updated without a separate tool like
kunit.py parsing the KTAP.

Indeed, my personal preference is that this log-based way of doing
expectations is probably best kept as a last resort. i.e.,
1. Try to add a hook to the code which prints the message, which can
then fail the test (or set a flag for the test to check later). This
probably needs some better KUnit-side helpers to be truly ergonomic,
but at least avoids too strict a dependency on the exact formatting of
the log messages.
2. If that doesn't work, use console tracepoints or similar to
implement an EXPECT_BEGIN() / EXPECT_END() or similar API entirely
within the kernel.
3. Only if we can't come up with a working way of doing the former
options, resort to adding "EXPECT:" lines and having a parser pick up
on this.

One of the downsides of doing "EXPECT" lines in KTAP is that it'll
suddenly be much more dependent on the exact layout of the tests, as
we'd need to be able to override a test result if an expectation fails
(at least, to maintain the KUnit structure). And overriding a result
which is already in the output seems really, really ugly.

There's a patch to the KASAN tests to move from doing option 1 to
option 2 above (in order to better support RCU, which didn't work with
the hook):
https://lore.kernel.org/all/ebf96ea600050f00ed567e80505ae8f24...@google.com/

> > threads and expect to start a discussion thread on this specific
> > topic in the KTAP Specification V2 context. I expect the discussion
> > to result in a different implementation than what DT unittests are
> > using (bike shedding likely to ensue) but whatever is agreed to
> > should be easy for DT to switch to.
>
> The link to the KTAP Specification Version 2 process and progress is:
>
> https://elinux.org/Test_Results_Format_Notes#KTAP_version_2
>

Thanks! We've got a few more KTAP ideas to air, so will hopefully send
those out soon!

Cheers,
-- David

[Frank Rowand]

Yes, I totally agree with that. If there is a reasonable way to
implement. But in the DT unittest world, I have not found a
reasonable way. Adding hooks is suggested below, but for DT
unittest _I_ (opinion) do not find that reasonable. I voice no
vote for kunit - that decision is up to the kunit crowd.

>
> Indeed, my personal preference is that this log-based way of doing
> expectations is probably best kept as a last resort. i.e.,
> 1. Try to add a hook to the code which prints the message, which can
> then fail the test (or set a flag for the test to check later). This
> probably needs some better KUnit-side helpers to be truly ergonomic,
> but at least avoids too strict a dependency on the exact formatting of
> the log messages.

I'm not a fan of hooks. I see them as a maintenance burden, dependent
upon the source version of the object being tested, yet another
thing that can go wrong, and adds complexity to creating a test
environment and running the test. Again, this just a personal
opinion, and I'm not voting for or against this for kunit.

> 2. If that doesn't work, use console tracepoints or similar to
> implement an EXPECT_BEGIN() / EXPECT_END() or similar API entirely
> within the kernel.

Isn't this just another hook? So same opinion.

> 3. Only if we can't come up with a working way of doing the former
> options, resort to adding "EXPECT:" lines and having a parser pick up
> on this.

Again, don't let my opinion affect the voting between 1, 2, 3, or other
for kunit.

>
> One of the downsides of doing "EXPECT" lines in KTAP is that it'll
> suddenly be much more dependent on the exact layout of the tests, as
> we'd need to be able to override a test result if an expectation fails
> (at least, to maintain the KUnit structure). And overriding a result
> which is already in the output seems really, really ugly.

I don't understand "dependent on the exact layout of the tests".
If you are saying that the test result parser has to figure out
which test result to override, that has not been an issue in
the cases that I use EXPECTs in DT unittest. The EXPECT begin and
EXPECT end have always immediately surrounded a single test, so
when the parser processes the EXPECT end, only the most recent
test result could be overridden. This has worked because the
kernel warning and error messages have been from kernel action
that happens synchronously with the test. If the test prods the
kernel in a way that results in the kernel performing an
asynchronous activity (eg in another thread), then it becomes
more complex to structure the EXPECT end -- I would imagine that the
test would have to block on the asynchronous activity just before
reporting the normal KTAP status result for the test (and the
EXPECT end would normally be just after reporting the KTAP
status result for the test).

I agree with overriding being ugly. For the DT unittest results
parser, the EXPECT summary results are reported separately from
the individual test summary results. The parser also flags the
EXPECT failure in line with the normal individual test result
lines.

I see both parsing results as valid, and as a policy choice for
each test parser.

>
> There's a patch to the KASAN tests to move from doing option 1 to
> option 2 above (in order to better support RCU, which didn't work with
> the hook):
> https://lore.kernel.org/all/ebf96ea600050f00ed567e80505ae8f24...@google.com/
>
>
>>> threads and expect to start a discussion thread on this specific
>>> topic in the KTAP Specification V2 context. I expect the discussion
>>> to result in a different implementation than what DT unittests are
>>> using (bike shedding likely to ensue) but whatever is agreed to
>>> should be easy for DT to switch to.
>>
>> The link to the KTAP Specification Version 2 process and progress is:
>>
>> https://elinux.org/Test_Results_Format_Notes#KTAP_version_2
>>
>
> Thanks! We've got a few more KTAP ideas to air, so will hopefully send
> those out soon!

Glad to hear, I'm hoping that process starts progressing a bit.

-Frank

[Frank Rowand]

Adding one more thought here so I don't forget it before the topic picks
up again in the KTAP version 2 world...

The test parser could generate an artificial subtest test case status line
or normal test case status line to report the result of the EXPECT. This
also is ugly because it is creating a new requirement on the parser vs the
expectations in the KTAP plan line (the plan line could include the EXPECT
in the number of tests count, but then the raw KTAP test output would be
missing the artificial EXPECT test result). No need to hash out details
here, just a thought...

-Frank

[David Gow]

I definitely agree that they've got their problems, and aren't the
right solution for every test.

That being said, I think a few of those problems also apply to
expecting individual error lines, which are basically doing the same
thing, just less explicitly (though with the advantage of serving
another real-world purpose).

> >> 2. If that doesn't work, use console tracepoints or similar to
> >> implement an EXPECT_BEGIN() / EXPECT_END() or similar API entirely
> >> within the kernel.
> >
> > Isn't this just another hook? So same opinion.
> >

I see what you mean. I guess the distinction I was trying to draw was
between a specific hook, implemented as such explicitly on both sides,
and a generic mechanism for console-message-based expectations.

So the difference is that, once the EXPECT_BEGIN()/EXPECT_END() macros
have been implemented this way, the uses of them should look the same.

> >> 3. Only if we can't come up with a working way of doing the former
> >> options, resort to adding "EXPECT:" lines and having a parser pick up
> >> on this.
>
> Adding one more thought here so I don't forget it before the topic picks
> up again in the KTAP version 2 world...
>
> The test parser could generate an artificial subtest test case status line
> or normal test case status line to report the result of the EXPECT. This
> also is ugly because it is creating a new requirement on the parser vs the
> expectations in the KTAP plan line (the plan line could include the EXPECT
> in the number of tests count, but then the raw KTAP test output would be
> missing the artificial EXPECT test result). No need to hash out details
> here, just a thought...
>

Yeah, I think if we have this done at the parser level, our options
are either that or an override.

For KUnit, I think the override makes much more sense, as logically,
any expectation would be considered part of an existing test case.
Maybe we could treat an override as a "subtest" of the current test,
but injecting a test case anywhere else would go pretty seriously
against the KUnit model.

> -Frank
>
> >
> > Again, don't let my opinion affect the voting between 1, 2, 3, or other
> > for kunit.
> >
> >>
> >> One of the downsides of doing "EXPECT" lines in KTAP is that it'll
> >> suddenly be much more dependent on the exact layout of the tests, as
> >> we'd need to be able to override a test result if an expectation fails
> >> (at least, to maintain the KUnit structure). And overriding a result
> >> which is already in the output seems really, really ugly.
> >
> > I don't understand "dependent on the exact layout of the tests".
> > If you are saying that the test result parser has to figure out
> > which test result to override, that has not been an issue in
> > the cases that I use EXPECTs in DT unittest. The EXPECT begin and
> > EXPECT end have always immediately surrounded a single test, so
> > when the parser processes the EXPECT end, only the most recent
> > test result could be overridden. This has worked because the
> > kernel warning and error messages have been from kernel action
> > that happens synchronously with the test. If the test prods the
> > kernel in a way that results in the kernel performing an
> > asynchronous activity (eg in another thread), then it becomes
> > more complex to structure the EXPECT end -- I would imagine that the
> > test would have to block on the asynchronous activity just before
> > reporting the normal KTAP status result for the test (and the
> > EXPECT end would normally be just after reporting the KTAP
> > status result for the test).

Okay: I agree 100% with you there.

I think the difference I was thinking of is more whether expectations
are considered part of an existing test (which may need overriding),
or exist as their own separate test result (as you suggest in the
follow-up email above).

> >
> > I agree with overriding being ugly. For the DT unittest results
> > parser, the EXPECT summary results are reported separately from
> > the individual test summary results. The parser also flags the
> > EXPECT failure in line with the normal individual test result
> > lines.
> >
> > I see both parsing results as valid, and as a policy choice for
> > each test parser.
> >

I agree that each parser should have some leeway here, but do think we
want to make sure the results have some sensible, standardised
interpretation, so that we can use parsers interchangeably without
getting totally inconsistent results. That's the big advantage of
standardisation, after all.

My philosophical objection to overriding is that it's really confusing
to have an "ok" line in the results, indicating that a test has
passed, when the test has in fact failed (because the expectation
doesn't match). This gets worse when subtests are considered, and we
have these misleading results bubbled up to reported overall "suite"
results.

I guess one solution is to have an extra layer of parsing, which takes
raw kernel output, verifies the expectations, and then outputs
"processed KTAP", with all of the final results resolved. But that's
ugly in a way, too.

> >>
> >> There's a patch to the KASAN tests to move from doing option 1 to
> >> option 2 above (in order to better support RCU, which didn't work with
> >> the hook):
> >> https://lore.kernel.org/all/ebf96ea600050f00ed567e80505ae8f24...@google.com/
> >>
> >>
> >>>> threads and expect to start a discussion thread on this specific
> >>>> topic in the KTAP Specification V2 context. I expect the discussion
> >>>> to result in a different implementation than what DT unittests are
> >>>> using (bike shedding likely to ensue) but whatever is agreed to
> >>>> should be easy for DT to switch to.
> >>>
> >>> The link to the KTAP Specification Version 2 process and progress is:
> >>>
> >>> https://elinux.org/Test_Results_Format_Notes#KTAP_version_2
> >>>
> >>
> >> Thanks! We've got a few more KTAP ideas to air, so will hopefully send
> >> those out soon!
> >
> > Glad to hear, I'm hoping that process starts progressing a bit.
> >

Yeah. I'll shift further discussion of this to a KTAP proposal: I
don't want to derail this thread too much further.

We'll keep looking at fully in-kernel ways of achieving similar things
in the meantime.

Cheers,
-- David

[Stephen Boyd]

Quoting David Gow (2023-03-10 22:42:24)

> Hmm... I'd've thought that shouldn't be a problem: kunit.py should
> ignore most messages during a test, unless it can't find a valid
> result line. What does the raw KTAP output look like? (You can get it
> from kunit.py by passing the --raw_output option).
>

I rebased and retried on v6.3-rc1 and it isn't a problem. Maybe there
was some problem on v6.2?