One of the goals for the 4.2 release is for
xl to have feature parity with
xm for the most important functions. But along the way, we’ve also been adding a number of improvements to the interface as well. One of the ways in which xl has changed and improved the interface is in passing through pci devices directly to VMs.
As you may know, Xen has for several years had the ability to “pass through” a pci device directly to a guest, allowing that guest to control the driver. This has several applications, including driver domains and increased performance for graphics or networking.
To pass through a device, you need to find out its BDF (Bus, Device, Function). A BDF now consists of three or four numbers in this format: