On Tue, 23 Apr 2019 01:41:57 -0400 Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > On Tue, Apr 23, 2019 at 09:21:00AM +0800, Alex Williamson wrote: > > On Mon, 22 Apr 2019 21:01:52 -0400 > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > On Mon, Apr 22, 2019 at 10:39:50PM +0800, Alex Williamson wrote: > > > > On Fri, 19 Apr 2019 04:35:04 -0400 > > > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > > > > > device version attribute in mdev sysfs is used by user space software > > > > > (e.g. libvirt) to query device compatibility for live migration of VFIO > > > > > mdev devices. This attribute is mandatory if a mdev device supports live > > > > > migration. > > > > > > > > The Subject: doesn't quite match what's being proposed here. > > > > > > > > > It consists of two parts: common part and vendor proprietary part. > > > > > common part: 32 bit. lower 16 bits is vendor id and higher 16 bits > > > > > identifies device type. e.g., for pci device, it is > > > > > "pci vendor id" | (VFIO_DEVICE_FLAGS_PCI << 16). > > > > > > > > What purpose does this serve? If it's intended as some sort of > > > > namespace feature, shouldn't we first assume that we can only support > > > > migration to devices of the same type? Therefore each type would > > > > already have its own namespace. Also that would make the trailing bit > > > > of the version string listed below in the example redundant. A vendor > > > > is still welcome to include this in their version string if they wish, > > > > but I think the string should be entirely vendor defined. > > > > > > > hi Alex, > > > This common part is a kind of namespace. > > > Because if version string is entirely defined by vendors, I'm worried about > > > if there is a case that one vendor's version string happens to deceive and > > > interfere with another vendor's version checking? > > > e.g. > > > vendor A has a version string like: vendor id + device id + mdev type > > > vendor B has a version string like: device id + vendor id + mdev type > > > but vendor A's vendor id is 0x8086, device id is 0x1217 > > > vendor B's vendor id is 0x1217, device id is 0x8086. > > > > > > In this corner case, the two vendors may regard the two device is > > > migratable but actually they are not. > > > > > > That's the reason for this common part that serve as a kind of namespace > > > that all vendors will comply with to avoid overlap. > > > > If we assume that migration can only occur between matching mdev types, > > this is redundant, each type already has their own namespace. > > > hi Alex, > do you mean user space software like libvirt needs to first check whether > mdev type is matching and then check whether version is matching? > > if user space software only checks version for migration, it means vendor > driver has to include mdev type in their vendor proprietary part string, > right? Can't userspace simply check for the driver in use and only then check the version attribute? > Another thing is that could there be any future mdev parent driver that > applies to all mdev devices, just like vfio-pci? like Yi's vfio-pci-mdev > driver (https://lkml.org/lkml/2019/3/13/114)? Hm, I think that the vfio-pci-mdev driver then needs to expose information regarding compatibility (and not the core). -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
