[dpdk-dev] [PATCH v1 1/2] vfio: make API return values consistent

[Burakov, Anatoly]

On 28-Oct-21 3:53 PM, Thomas Monjalon wrote:
> 28/10/2021 13:32, Ferruh Yigit:
>> On 10/28/2021 12:11 PM, Xia, Chenbo wrote:
>>>> -----Original Message-----
>>>> From: Burakov, Anatoly <anatoly.burakov at intel.com>
>>>> Sent: Thursday, October 28, 2021 6:30 PM
>>>> To: Xia, Chenbo <chenbo.xia at intel.com>; dev at dpdk.org
>>>> Subject: Re: [dpdk-dev] [PATCH v1 1/2] vfio: make API return values consistent
>>>>
>>>> Hi Chenbo,
>>>>
>>>>> And do we need backport? As 'return -1' does not align with the API doxygen.
>>>>>
>>>>> Thanks,
>>>>> Chenbo
>>>>>
>>>> Maybe it's the FreeBSD implementation that needs to be adjusted then,
>>>> because none of those functions are valid on FreeBSD, and the
>>>> documentation for VFIO functions explicitly mentions that on FreeBSD,
>>>> they should return an error. I went with adjusting Linux implementation
>>>> to minimize the amount of changes we have to make (and only change code
>>>> path that no one uses in the first place), but maybe that was a wrong
>>>> decision.
>>>>
>>>> I'm not sure if changing the API return value to match what was
>>>> documented counts as an API change, so maybe backport to stable is not
>>>> advised here.
>>>
>>> It's not a API change. My point is whether VFIO is present, users just use
>>> the API to check if vfio support is there. In a kernel version that does not
>>> support VFIO, he uses 'if(rte_vfio_is_enabled(XXX))' to check as the doxygen
>>> says its return value should be 1 as true or 0 as false. He will get true (-1)
>>> but VFIO is not there. That's why I think it's a bug and should be backported.
>>>
>>> But I think we can first discuss if we should drop the dummy implementation
>>> as DPDK requires Linux kernel version >= 4.4 now so VFIO is always present.
>>> I think it depends on by saying 'DPDK requires kernel version >= 4.4'. It's
>>> a real _requirement_ or only a recommendation?
>>>
>>> Ferruh, David & Thomas, What do you think?
>>>
>>
>> My understanding is, it is a requirement. DPDK does not guarantee support for
>> kernels < 4.4.
> 
> Do we have a kernel version check at runtime?
> I think we should add a warning if running too old kernel.
> 

Perhaps we should (there's a `uname()` call, should be fairly 
straightforward to implement), but obviously this would be outside the 
scope for this patchset.

-- 
Thanks,
Anatoly