On Tue, 6 Feb 2018 17:20:08 +0200 Ran Shalit <ransha...@gmail.com> wrote:
> On Tue, Feb 6, 2018 at 4:56 PM, Alex Williamson > <alex.william...@redhat.com> wrote: > > On Tue, 6 Feb 2018 16:24:06 +0200 > > Ran Shalit <ransha...@gmail.com> wrote: > > > >> Hello, > >> > >> I need to write vfio userspace driver for pci express. > >> I've been searching for some examples of using vfio, but did not find any, > >> Is there a git/examples of userspace application using vfio ? > > > > git://git.qemu.org/qemu.git > > git://dpdk.org/dpdk > > https://github.com/andre-richter/rVFIO > > https://github.com/MicronSSD/unvme > > https://github.com/awilliam/tests > > Thank you. > I am trying to understand how to use it with dma. > I've been checking now the links, but did not find yet in the above > example how to both map DMA memory and read/write from that memory. > I see that the above test git contains tests which map/unmap DMA, but > not reading/writing from that dma memory afterwards (there is a > seperate test which read/write from memory but without dma). > Is that correct or did I miss something ? Is there any example which > shows how to both map and then read/write ? Initiating DMA is device specific, you need to understand the programming model of the device for that. The vfio DMA ioctls only map the buffers through the IOMMU to allow that DMA, they don't control the device. The unit tests in the last link doesn't have any device specific code, they're only performing the mapping without actually initiating device DMA. The QEMU examples also mostly configure DMA but rely on native drivers within the guest VM to program the device to initiate DMA. The rVFIO project is also just a wrapper to make vfio more accessible to scripting languages, so I don't expect actual device driver code there. DPDK and the NVME driver should have actual driver code for the device though. In fact there's also an NVME project within QEMU that makes use of vfio that might have driver code. The simple logic though is that the DMA map ioctl takes a user provided virtual buffer and maps it through the IOMMU at the user provided IOVA (I/O virtual address). It's up to the user to make the device perform DMA using that IOVA. Note that the IOMMU address width is typically less than the user virtual address space, so identity mapping the IOVA to the virtual address is not a good strategy. > Another question, just to be sure I'm on the right direction. I wanted > to write pci express userspace driver (using real device, and not > related to virtualization). Is vfio a proper solution for this kind of > thing ? Yes, that's exactly what DPDK does. > I ask because there are no plenty of examples as I first expected, and > I try to understand why there are no many, (probably license issues ?) vfio is of course part of the kernel and GPL, but userspace drivers are not necessarily under the same license, so it is possible that the drivers themselves are more private. DPDK supports several NICs and I'd guess the NVME driver handles the standard NVME programming model and could therefore support devices from many vendors. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
