On 09/21/2016 12:51 PM, Alex Williamson wrote: > On Wed, 21 Sep 2016 11:19:17 +0800 > Jike Song <jike.song@xxxxxxxxx> wrote: > >> On 09/21/2016 12:24 AM, Alex Williamson wrote: >>> On Tue, 20 Sep 2016 10:50:47 +0800 >>> Jike Song <jike.song@xxxxxxxxx> wrote: >> >> /* trim the quotations */ >> >>>> Even performing a lightweight sanity check, would require vfio-mdev >>>> to be able to decode the ppos into a particular region, that means >>>> information of all regions should be stored in the framework. I guess >>>> it is not your preferred way :) >>> >>> There's certainly a trade-off there, we don't support dynamic regions, >>> the user expects them to be stable and the mdev-core code can expect >>> that also. It might simplify the vendor drivers slightly if the core >>> could perform such a basic sanity test, but the cost to do so would be >>> that the core needs to have an understanding of the region layout of >>> the device. >> >> I agree with why the requirement is, but I am suspicious that, >> if we assume the regions are stable, try to encode/decode that within >> the mdev-core framework - instead of vendor drivers - that is because >> we want mdev to be API compatible with vfio-pci? >> >> Being API compatible with vfio-pci is (IMHO) the most beautiful thing >> in current mdev design, but is it necessary to make it mandatory? >> How about letting the underlining vendor drivers to decide whether >> it is API compatible with vfio-pci, or will have a different set of >> userspace API? > > Are you assuming that I'm suggesting using VFIO_PCI_OFFSET_TO_INDEX in > the mdev core? We've been through that, I've rejected it, that's not > at all what I'm describing. The vfio bus driver defines the region > layout, but once defined it is fixed for a given device instance. A > user does not need to call ioctl(VFIO_DEVICE_GET_REGION_INFO) prior to > every region access to make sure the region offsets haven't changed > dynamically. If it's fixed to the user than it's also fixed to the > mdev core for a given device instance, so nothing prevents the core > code from doing its own enumeration of the region offsets and sizes and > caching them into data structures. That has nothing whatsoever to do > with vfio-pci and makes no assumptions about the layout of regions > within device fd. Thanks, > I misunderstood that previously and I understand the whole idea now. Thanks for the kind explanation! :) -- Thanks, Jike -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
