Abstract: An apparatus and method provide a protocol for communicating between an operating system that owns a shared resource and other operating systems that use the shared resource so that the operating systems that use the shared resource will not crash if the operating system that owns the shared resource is restarted. Messages are defined that allow handshaking between operating systems so that operating systems that share a resource will realize the resource will be unavailable for some period of time, and that allow resuming the sharing of the resource once the operating system that owns the shared resource is restarted.

Abstract: A memory tag mechanism creates a logical memory tag of a first length that corresponds to an I/O address of a second length. The memory tag is “logical” because it does not represent physical memory. When an I/O adapter device driver that expects an address of the first length is invoked, the memory tag is passed. When the I/O adapter device driver makes a call to the partition manager to convert the address of the first length (i.e., memory tag) to an I/O address of the second length, the partition manager detects that the passed address is a memory tag instead of a real address, and returns the corresponding I/O address. In this manner existing device drivers that expect addresses of the first length may be used for redirected DMA, which allows performing DMA operations directly from a shared I/O adapter in a hosting partition to memory in a hosted partition.