linux-kernel - Re: [RFC v2 1/2] vfio/pci: export common symbols in vfio-pci

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Date:   Wed, 20 Mar 2019 13:22:02 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe.brucker@....com" <jean-philippe.brucker@....com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 1/2] vfio/pci: export common symbols in vfio-pci

On Wed, 20 Mar 2019 11:49:37 +0000
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> > From: Alex Williamson [mailto:alex.williamson@...hat.com]
> > Sent: Wednesday, March 20, 2019 2:14 AM
> > To: Liu, Yi L <yi.l.liu@...el.com>
> > Subject: Re: [RFC v2 1/2] vfio/pci: export common symbols in vfio-pci
> > 
> > On Tue, 12 Mar 2019 16:18:22 +0800
> > "Liu, Yi L" <yi.l.liu@...el.com> wrote:
> >   
> > > This patch exports the following symbols from vfio-pci driver
> > > for vfio-pci alike driver. e.g. vfio-pci-mdev driver
> > >
> > > *) vfio_pci_set_vga_decode();
> > > *) vfio_pci_release();
> > > *) vfio_pci_open();
> > > *) vfio_pci_register_dev_region();
> > > *) vfio_pci_ioctl();
> > > *) vfio_pci_rw();
> > > *) vfio_pci_mmap();
> > > *) vfio_pci_request();
> > > *) vfio_pci_probe_misc();
> > > *) vfio_pci_remove_misc();
> > > *) vfio_err_handlers;
> > > *) vfio_pci_reflck_attach();
> > > *) vfio_pci_reflck_put();  
> > 
> > Exporting all these symbols scares me a bit.  They're GPL and we don't
> > guarantee a kernel ABI, but I don't really want to support arbitrary
> > use cases either.  What if we re-factored the shared bits into a common
> > file and just linked them together?  Thanks,  
> 
> Hi, Alex,
> 
> Before refactor the code, I'd like to check with you on the module
> parameters for the two modules. The existing vfio-pci driver has
> some module parameters. e.g. ids, nointxmask, disable_idle_d3.
> For future usage and maintain, I think it is better to let the two
> drivers have same parameters. However, I'm not 100% on whether
> we want to allow user load vfio-pci.ko and vfio-pci-mdev.ko with
> different parameter value? e.g. load vfio-pci.ko with nointxmask=false
> while load vfio-pci-mdev.ko with nointxmask=true. How about your
> opinion on it?

Hi Yi,

I agree that it makes sense to retain the module options for the mdev
wrapped version, but I expect we should also allow dissimilar user
settings.  If those lived in the common code that gets linked separately
with each module, that should work fine, I think.  We can worry about
refactoring for future driver that might not want those options later.
Thanks,

Alex