Date Added: Dec 2010
Para-virtualization presents a wide variety of issues to Operating Systems. One of these is presenting virtual devices to the para-virtualized operating system, as well as the device drivers which handle these devices. With the increase of virtualization in the Linux kernel, there has been an influx of unique drivers to handle all of these new virtual devices, and there are more devices on the way. The current state of Linux has four in-tree versions of a virtual network device (IBM pSeries Virtual Ethernet, IBM iSeries Virtual Ethernet, UML Virtual Network Device, and TUN/TAP) and numerous out-of-tree versions (one for Xen, VMware, 3leaf, and many others). Also, there are a similar number of block device drivers.