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From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Thread-Topic: [dpdk-dev] [PATCH] vfio: don't silently drop VFIO support
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Date: Wed, 22 Apr 2015 08:59:51 +0000
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Subject: Re: [dpdk-dev] [PATCH] vfio: don't silently drop VFIO support
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Hi Stephen,

> > Hi Stephen,
> >
> > > The VFIO_PRESENT #define was a landmine and we hit it.
> > > The DPDK has a config system and it should be used rather than
> > > silently dropping a feature during build only to have it fail at run =
time.
> > >
> > > If VFIO is configured, and the kernel headers are not present the
> > > build should fail. Rather than leaving developers puzzling why the
> > > build system (with old kernel headers) produced non functioning DPDK
> > > and their system (with new kernel headers) produced correctly working
> DPDK.
> > >
> > > As a matter of policy, really no code should be looking at
> > > <linux/version.h> except for kernel drivers with compat files.
> >
> > In theory, I agree with you. In practice however, this change will
> unconditionally break builds on pre-VFIO kernels (<3.6).
>=20
> If someone is building with an older kernel, then they should change the
> config.
>=20

Well, it's not like this is immediately obvious to anyone building DPDK. Wi=
th your patch, the "out-of-the-box" experience is no longer there, since on=
e now has to figure out why it's not building, go edit config files, et al,=
 which is easy for you and me, but may not be easy for someone dealing with=
 DPDK for the first time.

I agree that both situations aren't ideal, it just seems to me that not bui=
lding VFIO by default is better in that sense (EAL will show a warning mess=
age saying that VFIO isn't enabled, but the code will actually compile). Of=
 course, the best of both worlds would be something like a configure script=
.

Thanks,
Anatoly