Re: [dpdk-dev] [PATCH v8 2/3] build: use Python pmdinfogen

["Kinsella, Ray" <mdr@ashroe.eu>]

On 23/01/2021 11:38, Thomas Monjalon wrote:
> 22/01/2021 23:24, Dmitry Kozlyuk:
>> On Fri, 22 Jan 2021 21:57:15 +0100, Thomas Monjalon wrote:
>>> 22/01/2021 21:31, Dmitry Kozlyuk:
>>>> On Wed, 20 Jan 2021 11:24:21 +0100, Thomas Monjalon wrote:  
>>>>> 20/01/2021 08:23, Dmitry Kozlyuk:  
>>>>>> On Wed, 20 Jan 2021 01:05:59 +0100, Thomas Monjalon wrote:    
>>>>>>> This is now the right timeframe to introduce this change
>>>>>>> with the new Python module dependency.
>>>>>>> Unfortunately, the ABI check is returning an issue:
>>>>>>>
>>>>>>> 'const char mlx5_common_pci_pmd_info[62]' was changed
>>>>>>> to 'const char mlx5_common_pci_pmd_info[60]' at rte_common_mlx5.pmd.c    
>>>>>>
>>>>>> Will investigate and fix ASAP.  
>>>>
>>>> Now that I think of it: strings like this change every time new PCI IDs are
>>>> added to a PMD, but AFAIK adding PCI IDs is not considered an ABI breakage,
>>>> is it? One example is 28c9a7d7b48e ("net/mlx5: add ConnectX-6 Lx device ID")
>>>> added 2020-07-08, i.e. clearly outside of ABI change window.  
>>>
>>> You're right.
>>>
>>>> "xxx_pmd_info" changes are due to JSON formatting (new is more canonical),
>>>> which can be worked around easily, if the above is wrong.  
>>>
>>> If the new format is better, please keep it.
>>> What we need is an exception for the pmdinfo symbols
>>> in the file devtools/libabigail.abignore.
>>> You can probably use a regex for these symbols.
>>
>> This would allow real breakages to pass ABI check, abidiff doesn't analyze
>> variable content and it's not easy to compare. Maybe later a script can be
>> added that checks lines with RTE_DEVICE_IN in patches. There are at most 32 of
>> 5494 relevant commits between 19.11 and 20.11, though.
>>
>> To verify there are no meaningful changes I ensured empty diff between
>> results of the following command for "main" and the branch:
>>
>> 	find build/drivers -name '*.so' -exec usertools/dpdk-pmdinfo.py
> 
> For now we cannot do such check as part of the ABI checker.
> And we cannot merge this patch if the ABI check fails.
> I think the only solution is to allow any change in the pmdinfo variables.
> 

So my 2c on this is that this is an acceptable work-around for the v21 (DPDK v20.11) ABI.
However we are going to end up carrying this rule in libabigail.ignore indefinitely.

Would it make sense to just fix the size of _pmd_info to some reasonably large value - 
say 128 bytes, to allow us to drop the rule in the DPDK 21.11 v22 release?

Ray K