Intel ZT 4901 manual Switchover API, Switchover Scenarios and Theory of Operation

Redundant Host API

This function can be used to enumerate devices nested below physical slots if a PCI-PCI bridge occupies the physical slot. To get information about all devices at the next nesting level, this function should be called with the physical slot number and slot path to the immediate parent bridge. This slot path is taken from the slot information structure for the immediate parent. To enumerate devices immediately nested below the bridge in the physical slot, the caller should pass the slot path from the slot information structure obtained via RhGetPhysicalSlotInformation.

The returned information is represented by the array of structures of variable length. Each structure describes one device located immediately below the parent PCI-PCI bridge. The total length of the array is returned in the location pointed by pActualSize. If some of the information structures identify corresponding devices as PCI-PCI bridges, the caller can go deeper and enumerate the PCI devices below that bridge using this function.

6.2.5Switchover API

6.2.5.1Switchover Scenarios and Theory of Operation

6.2.5.1.1Fully Cooperative Switchover

In the cooperative switchover scenario, before giving up control over a domain, the owning host first prepares the PCI devices on this domain for switchover by gracefully shutting down operation on them and stopping the device drivers working with these devices. This operation is called software disconnection. This step is taken to ensure that the PCI devices appear to the new owner in a known state and that no transactions in progress are lost.

The exact meaning of software disconnection depends on the devices in the domain and their drivers. For device drivers that are not switchover-aware, software disconnection means shutdown of the corresponding devices and removal of all their software representations (device objects and so forth). Switchover-aware drivers may use “warmer” methods of preparation for switchover, keeping the device active to some degree during the switchover but preventing it from doing any damage to the new owning host immediately after the switchover (for example, preventing outstanding DMA transactions from this device to the host during the switchover).

Cooperative switchover can be initiated either by the owning host (in which case it voluntarily gives up control of this domain), or by the new owner of the domain, or by some third-party host. In the last two cases, an inter-host communication channel is used to request the owning host to initiate software disconnection. In all cases, software disconnection is initiated by calling the RhPrepareForSwitchover function.

Once started, software disconnection can be rejected by software (if, for example, a PCI device in the domain performs an important operation that cannot be interrupted). Software disconnection can also be left pending for a long time (for example, awaiting completion of an important transaction). The function RhPrepareForSwitchover is asynchronous and does not wait for completion of software disconnection. The current software connection state, associated with the domain, can be used to track the progress of the software disconnection operation.

The initial software connection state of the domain is INACTIVE. For a domain in the normal state, the software connection state is CONNECTED. When software disconnection is initiated for a domain, the corresponding state becomes DISCONNECTING and stays DISCONNECTING while software disconnection is pending for the domain. When software disconnection completes successfully, the state goes to DISCONNECTED. If software disconnection is terminated unsuccessfully, the state goes back to CONNECTED.

High Availability Software for the Intel® NetStructureTM ZT 4901 Technical Product Specification 61