Device configuration for machines running in PR/SM mode

Defining devices to an LPAR

Typical IBM Z® and IBM® LinuxONE systems run numerous operating system instances in parallel and connect to a considerable number of storage, network, and other peripheral devices. In this environment, device access must be controlled.

• Workload isolation demands selective and controlled device access.
• Operating systems expend cycles, time, and memory to manage each device. For example, on Linux®, udev creates structures for each registered device.

Data centers with discrete host systems can use physical cabling between hosts and peripheral devices to manage device access. On IBM Z and IBM LinuxONE systems with their logical partitions (LPARs), much of this cabling would need to be within the hardware system itself.

Instead of cables, a hardware configuration controls which LPAR has access to which I/O device. The hardware configuration is specified in an input/output configuration data set (IOCDS). In PR/SM mode, users run the Hardware Configuration Definition (HCD) program to create an IOCDS, which they can then activate on the machine to define LPARs and the I/O configuration. In Dynamic Partition Manager (DPM) mode, users instead create and manage partitions and I/O directly through the HMC user interfaces or APIs, so a separate HCD program is not required.

Controlling device availability on Linux

Use cio_ignore to create and maintain a list of devices to be ignored by Linux.

The hardware configuration already limits the I/O devices that are available to a Linux instance. The cio_ignore feature provides another control point on Linux for channel-attached CCW devices. With cio_ignore, you can create and maintain a list of channel-attached CCW devices to be ignored by Linux. For details about the command, see cio_ignore - Manage the I/O exclusion list.

Configuring devices in Linux