Device Classification

Sun Cluster introduces a new device classification scheme. These new classifications are based on the extended behavior of the devices in a Sun Cluster environment.

Enumerated Devices

ENUMERATED_DEV

Node Specific Devices

NODESPECIFIC_DEV

Global Devices

GLOBAL_DEV

Node Bound Devices

NODEBOUND_DEV

The ddi_create_minor_node(9F) routine has been enhanced to add the capability of reporting the additional device classification of the device minor nodes created by the device driver. The device node class is specified using the flag parameter. If the device class is not indicated, the default class for pseudo devices will be NODESPECIFIC_DEV and for physical devices will be ENUMERATED_DEV. These device classes do not effect the creation of the device node in a non-clustered environment; but they are required for device drivers intended for use in a clustered environment. The device categories are described in the following sections.

Enumerated Devices

Enumerated devices are physical devices with a one-to-one correspondence between a particular device node and a host where that device node is present. Examples of this category include various disk and tape devices, such as /dev/dsk/c0t0d0s0 and /dev/rmt/0l. Nearly all physical devices belong to this category. This is the default category for all non-pseudo devices.

Node Specific Devices

Node specific devices include devices that report particular information about the host where the device node is opened. An example of such a device is the /dev/kmem device. Opening this device gives access to host-specific information on the local host. Administrative pseudo device nodes used in configuring or gathering information about a particular device driver also fit this category. The Sun Cluster software ensures the creation of two user device nodes for each instance of a kernel device node in the cluster, so that the intended device node can be accessed both locally and remotely.

Global Devices

Global devices are node invariant pseudo devices such as /dev/ip. In principle, the open instance of a device, such as ip or tcp, does not depend on which host, in the cluster, the open occurs. A single copy of each device is in the kernel. All device I/O requests for this device class are performed locally and the device node can be accessed by a remote host within the cluster. This is the default behavior for all pseudo devices in the system.

Node Bound Devices

A node bound device is a pseudo device that maintains a cluster-wide state. This device should, in principle, be opened on one node only. Devices such as /dev/ticotsord belong to this class (see the ticotsord(7D) man page). Highly available devices with automatic fail-over also belong to this class. Only one pseudo node is present but all opens are directed to the same node, with the exception of HA devices, where the hosting node might change, transparent to the device user.