On Fri, 10 Sep 2021 10:38:50 -0300 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Fri, Sep 10, 2021 at 01:10:46PM +0100, Christoph Hellwig wrote: > > On Thu, Sep 09, 2021 at 04:38:45PM -0300, Jason Gunthorpe wrote: > > > Every driver just emits a static string, simply feed it through the ops > > > and provide a standard sysfs show function. > > > > Looks sensible. But can you make the attribute optional and add a > > comment marking it deprecated? Because it really is completely useless. > > We don't version userspace APIs, userspae has to discover new features > > individually by e.g. finding new sysfs files or just trying new ioctls. > > To be honest I have no idea what side effects that would have.. > > device code search tells me libvirt reads it and stuffs it into some > XML > > Something called mdevctl touches it, feeds it into some JSON and > other stuff.. > > qemu has some VFIO_DEVICE_API_* constants but it is all dead code > > I agree it shouldn't have been there in the first place > > Cornelia? Alex? Any thoughts? It's not a version, it's a means for userspace to determine the basic API for an mdev device without needing to go through the process of creating a container, adding the group, setting an IOMMU type, opening the device before being able to call VFIO_DEVICE_GET_INFO to determine the API. For example, it wouldn't make sense for libvirt to attach a vfio-ccw device to a PCIe root port in a VM. It's a means to say this mdev device is a vfio-pci or that mdev device is a vfio-ccw. If it were optional, then management tools would have no basic idea how to attach the device to a VM without gaining access to the device themselves. Thanks, Alex
