Re: [PATCH v6 3/7] kunit: Add kunit wrappers for (root) device creation

[Matti Vaittinen <mazziesaccount@gmail.com>]

Hi David & Greg and thanks for working with this!

On 3/28/23 15:45, David Gow wrote:
> Thanks, Gred and Matti.
> 
> On Mon, 27 Mar 2023 at 20:38, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
>>
>> On Mon, Mar 27, 2023 at 03:20:06PM +0300, Matti Vaittinen wrote:
>>> On 3/27/23 15:01, Greg Kroah-Hartman wrote:
>>>> On Mon, Mar 27, 2023 at 02:34:02PM +0300, Matti Vaittinen wrote:
> 
> I'm happy to keep working on this, but would definitely appreciate
> your feedback.
> 
> I've put my work-in-progress code here:
> https://kunit.googlesource.com/linux/+/refs/heads/kunit/device-helpers%5E%21/#F0
> 
> It creates a "kunit" bus, and adds a few helpers to create both
> devices and drivers on that bus, and clean them up when the test
> exits. It seems to work on all of the tests which used
> root_device_register so far (except those -- only
> test_iio_find_closest_gain_low so far -- which create multiple devices
> with the same name, as the driver name won't be unique),

I wouldn't worry about it for as long as it's just because an iio-gts 
test does something silly. Those tests are currently only in my personal 
playground and changing those tests should be pretty trivial.

And right after saying that - the test_iio_find_closest_gain_low test does

a) register a 'test' device
b) perform test on devm_ API
c) unregister the 'test' device

d) register a 'test' device (same name as at step a)
e) perform test on devm_ API
f) unregister the 'test' device

My assumption is that the test device would be gone after step c) 
because there should be no references to it anywhere. Hence, I wonder 
why registering at step d) fails? (Or did I misunderstand something?)

> and the drm
> tests work fine when ported to it as well.
> 
> There's still a lot of cleanup to do and questions which need
> answering, including:
> - Working out how best to provide an owning module (it's currently
> just kunit, but probably should be the module which contains the
> actual tests)

Maybe there is something I am not seeing but how about wrapping the 
kunit_device_register() in a macro and getting the THIS_MODULE in 
caller's context?

> In any case, does this seem like the right way forward?

I am by no means an expert on this but this does look good to me. I 
would keep this as clean, lean and simple as possible in order to keep 
understanding / debugging the problems exposed by the tests as simple as 
possible. At some point someone is wondering why a test fails, and ends 
up looking through these helpers to ensure problem is no lurking 
there... Hence, I'd kept the code there in minimum - meaning, I might 
not add kunit class or even a driver until tests require that. (Even if 
it would not look as good in the sysfs - as far as I understand the 
kunit sysfs entries are a 'test feature' which should not be present in 
'production systems'. This is not an excuse to make things bad - but (in 
my opinion) this is a good reason to prioritize simplicity.

Anyways, thanks for the work!

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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