On Tue, Dec 06, 2022 at 03:15:41PM -0400, Jason Gunthorpe wrote: > What the kernel is doing is providing the abstraction to link the > controlling function to the VFIO device in a general way. > > We don't want to just punt this problem to user space and say 'good > luck finding the right cdev for migration control'. If the kernel > struggles to link them then userspace will not fare better on its own. Yes. But the right interface for that is to issue the userspace commands for anything that is not normal PCIe function level to the controlling funtion, and to discover the controlled functions based on the controlling functions. In other words: there should be absolutely no need to have any special kernel support for the controlled function. Instead the controlling function enumerates all the function it controls exports that to userspace and exposes the functionality to save state from and restore state to the controlled functions. > Especially, we do not want every VFIO device to have its own crazy way > for userspace to link the controlling/controlled functions > together. This is something the kernel has to abstract away. Yes. But the direction must go controlling to controlled, not the other way around.
