linux-kernel - RE: [PATCH v4 11/12] samples: add vfio-mdev-pci driver

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Date:   Sat, 18 Jan 2020 14:23:45 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Cornelia Huck <cohuck@...hat.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: RE: [PATCH v4 11/12] samples: add vfio-mdev-pci driver

> From: Cornelia Huck [mailto:cohuck@...hat.com]
> Sent: Friday, January 17, 2020 1:40 AM
> To: Liu, Yi L <yi.l.liu@...el.com>
> Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver
> 
> On Thu, 16 Jan 2020 13:23:28 +0000
> "Liu, Yi L" <yi.l.liu@...el.com> wrote:
> 
> > > From: Cornelia Huck [mailto:cohuck@...hat.com]
> > > Sent: Wednesday, January 15, 2020 8:30 PM
> > > To: Liu, Yi L <yi.l.liu@...el.com>
> > > Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver
> > >
> > > On Tue,  7 Jan 2020 20:01:48 +0800
> > > Liu Yi L <yi.l.liu@...el.com> wrote:
> 
> > > > diff --git a/samples/Kconfig b/samples/Kconfig index
> > > > 9d236c3..50d207c 100644
> > > > --- a/samples/Kconfig
> > > > +++ b/samples/Kconfig
> > > > @@ -190,5 +190,15 @@ config SAMPLE_INTEL_MEI
> > > >  	help
> > > >  	  Build a sample program to work with mei device.
> > > >
> > > > +config SAMPLE_VFIO_MDEV_PCI
> > > > +	tristate "Sample driver for wrapping PCI device as a mdev"
> > > > +	select VFIO_PCI_COMMON
> > > > +	select VFIO_PCI
> > >
> > > Why does this still need to select VFIO_PCI? Shouldn't all needed
> > > infrastructure rather be covered by VFIO_PCI_COMMON already?
> >
> > VFIO_PCI_COMMON is supposed to be the dependency of both VFIO_PCI and
> > SAMPLE_VFIO_MDEV_PCI. However, the source code of VFIO_PCI_COMMON are
> > under drivers/vfio/pci which is compiled per the configuration of VFIO_PCI.
> > Besides of letting SAMPLE_VFIO_MDEV_PCI select VFIO_PCI, I can also
> > add a line in drivers/vfio/Makefile to make the source code under
> > drivers/vfio/pci to be compiled when either VFIO_PCI or
> > VFIO_PCI_COMMON are configed. But I'm afraid it is a bit ugly. So I
> > choose to let SAMPLE_VFIO_MDEV_PCI select VFIO_PCI. If you have other
> > idea, I would be pleased to know it. :-)
> 
> Shouldn't building drivers/vfio/pci/ for CONFIG_VFIO_PCI_COMMON already be
> enough (the Makefile changes look fine to me)? Or am I missing something obvious?

The problem is in the drivers/vfio/Makefile. If CONFIG_VFIO_PCI is not
selected then the pci/ directory is not compiled. Even CONFIG_VFIO_PCI=M,
it will throw error if SAMPLE_VFIO_MDEV_PCI=y. So I let SAMPLE_VFIO_MDEV_PCI
select CONFIG_VFIO_PCI all the same. I'm not sure if this is good. Or maybe
there is better way to ensure pci/ is compiled.

# SPDX-License-Identifier: GPL-2.0
vfio_virqfd-y := virqfd.o

obj-$(CONFIG_VFIO) += vfio.o
obj-$(CONFIG_VFIO_VIRQFD) += vfio_virqfd.o
obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
obj-$(CONFIG_VFIO_SPAPR_EEH) += vfio_spapr_eeh.o
obj-$(CONFIG_VFIO_PCI) += pci/
obj-$(CONFIG_VFIO_PLATFORM) += platform/
obj-$(CONFIG_VFIO_MDEV) += mdev/

Thanks,
Yi Liu