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

[Thomas Monjalon <thomas@monjalon.net>]

28/10/2021 13:32, Ferruh Yigit:
> On 10/28/2021 12:11 PM, Xia, Chenbo wrote:
> >> -----Original Message-----
> >> From: Burakov, Anatoly <anatoly.burakov@intel.com>
> >> Sent: Thursday, October 28, 2021 6:30 PM
> >> To: Xia, Chenbo <chenbo.xia@intel.com>; dev@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.