M-VIA Design

M-VIA Architecture

The VI Architecture Specification describes VIA as being composed of three main components: the VI Provider Library (VIPL); the VI Kernel Agent; and VI NICs. M-VIA further abstracts the Kernel Agent into the M-VIA Kernel Agent and one or more M-VIA Device Drivers. A VI Kernel Agent for specific hardware is realized by the combination of the M-VIA Kernel Agent and the M-VIA Device Driver for the hardware.

M-VIA Kernel Agent

The M-VIA Kernel Agent performs privileged operations on behalf the VI Provider Library and assists M-VIA Device Drivers with operations requiring operating system support.

The M-VIA Kernel Agent is divided into the following device independent functional components:

M-VIA Device Drivers

An M-VIA Device Driver is an abstraction of a VI NIC, and registers itself with the M-VIA Kernel Agent. The device informs the Kernel Agent of its capabilities, such as whether it supports VIA directly in hardware, its native MTU size, the maximum number of VIA descriptors that can be queued for transmission, etc. The device also registers device specific functions to be used by the modular managers of the Kernel Agent layer. The developer of the M-VIA Device Driver has the option of overriding any and all of the default functionality provided by the M-VIA Kernel Agent layer. For example, if a device which provides native VIA hardware support uses its own mechanism for registering memory, it may completely replace the Registered Memory Manager with an implementation of its own. The ability to override all of the default functionality of the M-VIA Kernel Agent layer should allow any natively supported or software emulated VIA device to be supported by M-VIA. However, it is conceivable that a device with native hardware support for VIA which deviates from the recommendations in the VI Architecture Specification would not be supported.

Device Classes

Many commodity network interfaces can be logically grouped into common categories such as Ethernet, ATM, FDDI, etc. In order to promote wire level interoperability and rapid development through code reuse, Modular VIA employs the use of Device Classes. M-VIA uses slightly finer-grained classes than network types, such as the EtherRing category mentioned above. Device Classes enable common routines for a class of network interfaces to be shared by KAD implementations. Such routines include operations like the construction and interpretation of media specific VIA headers and mechanisms for enabling VIA to co-exist with traditional networking protocols, i.e. TCP/IP. While Device Classes are not explicitly supported by the M-VIA Device Driver layer, the Device Driver layer is designed to facilitate the use of such classes. Macros are used for communication between a KAD implementation and a device class, and these are integrated into a single loadable kernel module.

VI Provider Library

M-VIA contains a single VI Provider Library, which is interoperable with native hardware and software VIA devices developed within the Modular VIA framework. M-VIA Kernel Agent Drivers specify whether ioctl system calls or fast traps are used by the VI Provider Library to call time-sensitive VI Kernel Agent services. M-VIA Device Drivers also specify weather the VIA Doorbell mechanism is supported directly in hardware as a true memory mapped doorbell or should be emulated with a fast trap.

M-VIA 1.0. Fri, 17 Sep 1999 09:13:43 -0700.
Copyright (C) 1998,1999 Berkeley Lab.