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Date: Tue, 26 Mar 2019 09:35:20 -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 Tue, 26 Mar 2019 12:37:37 +0000 "Liu, Yi L" <yi.l.liu@...el.com> wrote: > > From: Alex Williamson [mailto:alex.williamson@...hat.com] > > Sent: Tuesday, March 26, 2019 2:17 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 Sat, 23 Mar 2019 11:06:44 +0000 > > "Liu, Yi L" <yi.l.liu@...el.com> wrote: > > > Hi Alex, > > [...] > > > > > > > I tried to get a common file which includes the definitions of the module > > > options and the common interfaces and get it linked separately with each > > > module. It works well when linked separately by config the > > > CONFIG_VFIO_PCI=m and CONFIG_VFIO_PCI_MDEV=m in kernel > > > configuration file. CONFIG_VFIO_PCI_MDEV is a new Kconfig macro > > > for the mdev wrapped version driver. However, if building the vfio-pci > > > and the mdev wrapped version into kernel image (config the > > > CONFIG_VFIO_PCI=y and CONFIG_VFIO_PCI_MDEV=y), then the symbols > > > defined in the common file will be shared thus doesn't allow dissimilar > > > user settings. > > > > > > Per my understanding, I think we expect to allow simultaneous usage of > > > the two drivers. So I think the way above doesn't meet our expectation. > > > > I agree. They should be related in implementation only, from a user > > perspective they should be entirely separate. > > > > > I considered a possible proposal as below. May listen to your opinion > > > on it before heading to cook. Also, better idea is welcomed. :-) > > > > > > - get a common file includes interfaces which are common and have > > > input parameters to differentiate the calling from vfio-pci and the > > > wrapped version. e.g. vfio_pci_rw(). may call it as vfio_pci_common.c. > > > > > > - get another common file includes the definitions of the module options, > > > and the functions which referred the options. Define all of them as static. > > > may call it as common.c > > > > > > - get vfio_pci.c which includes the module_init/exit interfaces and driver > > > registration operations of vfio-pci.ko. This file should include the common.c > > > above to have same module options with the mdev wrapped version. > > > > > > - get vfio_pci_mdev.c which includes the module_init/exit interfaces and > > > driver registration operations of vfio-pci-mdev.ko. It should also include > > > the common.c above to have same module options with vfio-pci.ko. > > > > > > - Makefile: > > > vfio-pci-y := vfio_pci.o vfio_pci_common.o vfio_pci_intrs.o vfio_pci_rdwr.o > > vfio_pci_config.o > > > vfio-pci-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o > > > vfio-pci-$(CONFIG_VFIO_PCI_NVLINK2) += vfio_pci_nvlink2.o > > > > > > vfio-pci-mdev-y := vfio_pci_mdev.o vfio_pci_common.o vfio_pci_intrs.o > > vfio_pci_rdwr.o vfio_pci_config.o > > > vfio-pci-mdev-$(CONFIG_VFIO_PCI_IGD) += vfio_pci_igd.o > > > vfio-pci-mdev-$(CONFIG_VFIO_PCI_NVLINK2) += vfio_pci_nvlink2.o > > > > > > obj-$(CONFIG_VFIO_PCI) += vfio-pci.o > > > obj-$(CONFIG_VFIO_PCI_MDEV) += vfio-pci-mdev.o > > > > Each module needs it's own module_init/exit and will register its own > > struct pci_driver, which gives us separate control of the probe and > > Agreed. > > > remove callbacks. I think we want the drivers to have the same module > > parameters initially, but we don't necessarily want to require it for > > any future options, so we can duplicate the parameter declarations. > > Then to support the shared code, I think we can easily push nointxmask, > > disable_vga, and disable_idle_d3 into bools on the struct > > vfio_pci_device, which would be allocated and set by each module's > > probe function before calling the shared probe function. > > sounds good to me. > > > vfio_fill_ids() could take a pointer to the array to keep them separate > > between modules. > > Agreed. > > > I think that just leaves the config permission bits, > > vfio_pci_{un}init_perm_bits(). Could we use a simple atomic reference > > counter on those to potentially share them so they get initialized by > > the first caller and freed by the last user, at least in the case of > > both drivers being compiled statically into the kernel? Thanks, > > Sure, I can add it. The two modules will still share the cap_perms and > ecap_perms config bits when built statically in kernel. However, I think > such share is reasonable. I'll check if any other similar bits in other files. > > > Alex > > Thanks for the suggestions, Alex. Let me prepare another RFC. Thank Yi, I appreciate your work on this. Also, I wonder if we might want to reconsider placing this driver in samples, the Makefile might be a little bit ugly with paths back to drivers/vfio/pci, but I don't think we run into the same barriers as you did with previous approaches. Placing it in samples would at least alleviate any confusion that this isn't a vfio-pci replacement, but more of an mdev wrapper proof of concept. Thanks, Alex
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