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AIX Version 4.3 Kernel Extensions and Device Support Programming Concepts

Device Configuration Manager Overview

The Configuration Manager is a rule-driven program that automatically configures devices in the system during system boot and run time. When the Configuration Manager is invoked, it reads rules from the Configuration Rules object class and performs the indicated actions.

Devices in the system are organized in clusters of tree structures known as nodes. Each tree is a logical subsystem by itself. For example, the system node consists of all the physical devices in the system. The top of the node is the system device. Below the bus and connected to it are the adapters. The bottom of the hierarchy contains devices to which no other devices are connected. Most pseudo-devices, including low -function terminal ( HFT LFT ) and pseudo-terminal (pty) devices, are organized as separate tree structures or nodes.

Devices Graph

The Devices Graph: Examples of Connectivity and Dependence diagram provides an example of the connections and dependencies of devices in the system. "Understanding Device Dependencies and Child Devices" provides more information.

Configuration Rules

Each rule in the Configuration Rules (Config_Rules) object class specifies a program name that the Configuration Manager must execute. These programs are typically the configuration programs for the devices at the top of the nodes. When these programs are invoked, the names of the next lower-level devices that need to be configured are returned.

If the -m (mask) flag is not used, the cfgmgr command executes all of the rules for the specified phase. When a mask is specified, the cfgmgr command applies the mask to each rule for the phase. If the mask specified with the -m flag matches the boot_mask field from the configuration rules, the rule is executed. Otherwise, the cfgmgr command does not execute the rule. In this way, phase 1 of the boot process can be tailored for a particular type of boot (for example, DISK_BOOT).

The Configuration Manager configures the next lower-level devices by invoking the configuration methods for those devices. In turn, those configuration methods return a list of to-be-configured device names. The process is repeated until no more device names are returned. As a result, all devices in the same node are configured in transverse order. There are three different types of rules:

The system boot process is divided into two phases. In each phase, the Configuration Manager is invoked. During phase 1, the Configuration Manager is called with a -f flag, which specifies that phase = 1 rules are to be executed. This results in the configuration of base devices into the system, so that the root file system can be used. During phase 2, the Configuration Manager is called with a -s flag, which specifies that phase = 2 rules are to be executed. This results in the configuration of the rest of the devices into the system.

"Understanding System Boot Processing" in AIX Version 4.3 System Management Guide: Operating System and Devices contains diagrams that illustrate the separate step of system boot processing.

The Configuration Manager invokes the programs in the order specified by the sequence value in the rule. In general, the lower the sequence number within a given phase, the higher the priority. Thus, a rule with a 2 sequence number is executed before a rule with a sequence number of 5. An exception is made for 0 sequence numbers, which indicate a don't-care condition. Any rule with a sequence number of 0 is executed last. The Configuration Rules (Config_Rules) object class provides an example of this process.

If device names are returned from the program invoked, the Configuration Manager finishes traversing the node tree before it invokes the next program. Note that some program names may not be associated with any devices, but they must be included to configure the system.

Invoking the Configuration Manager

During system boot time, the Configuration Manager is run in two phases. In phase 1, it configures the base devices needed to successfully start the system. These devices include the root volume group, which permits the configuration database to be read in from the root file system.

In phase 2, the Configuration Manager configures the remaining devices using the configuration database from the root file system. During this phase, different rules are used, depending on the key switch position on the front panel. If the key is in service position, the rules for service mode are used. Otherwise, the phase 2 rules are used.

The Configuration Manager can also be invoked during run time to configure all the detectable devices that may have been turned off at system boot or added after the system boot. In this case, the Configuration Manager uses the phase 2 rules.

Related Information

Device Configuration Database Overview.

Configuration Rules Object Class.

Basic Device Configuration Procedures Overview.

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