Re: [PATCH RFC] kselftest: devices: Add test to detect missing devices

[Shuah Khan <skhan@linuxfoundation.org>]

On 8/1/24 13:15, Nícolas F. R. A. Prado wrote:
> On Wed, Jul 31, 2024 at 05:19:45PM -0600, Shuah Khan wrote:
>> On 7/24/24 15:40, Nícolas F. R. A. Prado wrote:
>>> Introduce a new test to identify regressions causing devices to go
>>> missing on the system.
>>>
>>> For each bus and class on the system the test checks the number of
>>> devices present against a reference file, which needs to have been
>>> generated by the program at a previous point on a known-good kernel, and
>>> if there are missing devices they are reported.
>>
>> Can you elaborate on how to generate reference file? It isn't clear.
> 
> Indeed, I'll make that information clearer in future versions.
> 
> The reference file is generated by passing the --generate-reference flag to the
> test:
> 
> ./exist.py --generate-reference
> 
> It will be printed as standard output.

How about adding an option to generate file taking filename?
Makes it easier to use.

> 
>>
>>>
>>> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
>>> ---
>>> Hi,
>>>
>>> Key points about this test:
>>> * Goal: Identify regressions causing devices to go missing on the system
>>> * Focus:
>>>     * Ease of maintenance: the reference file is generated programatically
>>>     * Minimum of false-positives: the script makes as few assumptions as possible
>>>       about the stability of device identifiers to ensure renames/refactors don't
>>>       trigger false-positives
>>> * How it works: For each bus and class on the system the test checks the number
>>>     of devices present against a reference file, which needs to have been
>>>     generated by the program at a previous point on a known-good kernel, and if
>>>     there are missing devices they are reported.
>>> * Comparison to other tests: It might be possible(*) to replace the discoverable
>>>     devices test [1] with this. The benefits of this test is that it's easier
>>>     to setup and maintain and has wider coverage of devices.
>>>
>>> Additional detail:
>>> * Having more devices on the running system than the reference does not cause a
>>>     failure, but a warning is printed in that case to suggest that the reference
>>>     be updated.
>>> * Missing devices are detected per bus/class based on the number of devices.
>>>     When the test fails, the known metadata for each of the expected and detected
>>>     devices is printed and some simple similitarity comparison is done to suggest
>>>     the devices that are the most likely to be missing.
>>> * The proposed place to store the generated reference files is the
>>>     'platform-test-parameters' repository in KernelCI [2].
>>
>> How would a user run this on their systems - do they need to access
>> this repository in KernelCI?
> 
> No, that repository would just be a place where people could find pre-generated
> reference files (which we'll be using when running this test in KernelCI), but
> anyone can always generate their own reference files and store them wherever
> they want.
> 

Thanks for the clarification. This might be good addition to the document.
I think this test could benefit from a README or howto

>>
>> This is what I see when I run the test on my system:
>>
>> make -C tools/testing/selftests/devices/exist/ run_tests
>> make: Entering directory '/linux/linux_6.11/tools/testing/selftests/devices/exist'
>> TAP version 13
>> 1..1
>> # timeout set to 45
>> # selftests: devices/exist: exist.py
>> # TAP version 13
>> # # No matching reference file found (tried './LENOVO,20XH005JUS.yaml')
> 
> First generate the reference file for your system like so:
> 
> tools/testing/selftests/devices/exist/exist.py --generate-reference > tools/testing/selftests/devices/exist/LENOVO,20XH005JUS.yaml
> 

Worked - I see

TAP version 13
# Using reference file: ./LENOVO,20XH005JUS.yaml
1..76

---
# Totals: pass:76 fail:0 xfail:0 xpass:0 skip:0 error:0


Things to improve:

- Have the script take a file instead of assuming that the reference file
   is in the current directory.
   e.g: exist.py -f reference_file

thanks,
-- Shuah