Re: [REGRESSION] changes to driver_override parsing broke DPDK script

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 09/08/2022 22:21, Bjorn Helgaas wrote:
> [+cc regressions list]
> 
> 23d99baf9d72 appeared in v5.19-rc1.
> 
> On Tue, Aug 09, 2022 at 11:29:43AM -0700, Stephen Hemminger wrote:
>> This commit broke the driver override script in DPDK.
>> This is an API/ABI breakage, please revert or fix the commit.
>>
>> Report of problem:
>> http://mails.dpdk.org/archives/dev/2022-August/247794.html

Thanks for the report. I'll take a look.

>>
>>
>> commit 23d99baf9d729ca30b2fb6798a7b403a37bfb800
>> Author: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>> Date:   Tue Apr 19 13:34:28 2022 +0200
>>
>>     PCI: Use driver_set_override() instead of open-coding
>>     
>>     Use a helper to set driver_override to the reduce amount of duplicated
>>     code.  Make the driver_override field const char, because it is not
>>     modified by the core and it matches other subsystems.
>>     
>>     Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
>>     Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>>     Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>>     Link: https://lore.kernel.org/r/20220419113435.246203-6-krzysztof.kozlowski@linaro.org
>>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>
>>
>> The script is sending single nul character to remove override
>> and that no longer works.

The sysfs API clearly states:
"and
 may be cleared with an empty string (echo > driver_override)."
Documentation/ABI/testing/sysfs-bus-pci

Sending other data and expecting the same result is not conforming to
API. Therefore we have usual example of some undocumented behavior which
user-space started relying on and instead using API, user-space expect
that undocumented behavior to be back.

Yay! I wonder what is the point to even describe the ABI if user-space
can simply ignore it?

Best regards,
Krzysztof