diff options
| -rw-r--r-- | introduction.tex | 66 |
1 files changed, 51 insertions, 15 deletions
diff --git a/introduction.tex b/introduction.tex index 0047af4..74454a2 100644 --- a/introduction.tex +++ b/introduction.tex @@ -1,30 +1,66 @@ \chapter{Introduction} -\section{Terminology} - -The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in \hyperref[intro:rfc2119]{[RFC2119]}. - +This document describes the specifications of the “virtio” family of +devices. These are devices are found in virtual environments, yet by +design they are not all that different from physical devices, and this +document treats them as such. This allows the guest to use standard +drivers and discovery mechanisms. + +The purpose of virtio and this specification is that virtual +environments and guests should have a straightforward, efficient, +standard and extensible mechanism for virtual devices, rather +than boutique per-environment or per-OS mechanisms. + + Straightforward: Virtio devices use normal bus mechanisms of + interrupts and DMA which should be familiar to any device driver + author. There is no exotic page-flipping or COW mechanism: it's just + a normal device. +\footnote{This lack of page-sharing implies that the implementation of the +device (e.g. the hypervisor or host) needs full access to the +guest memory. Communication with untrusted parties (i.e. +inter-guest communication) requires copying. +} + + Efficient: Virtio devices consist of rings of descriptors + for input and output, which are neatly separated to avoid cache + effects from both guest and device writing to the same cache + lines. + + Standard: Virtio makes no assumptions about the environment in which + it operates, beyond supporting the bus attaching the device. Virtio + devices are implemented over PCI and other buses, and earlier drafts + been implemented on other buses not included in this spec. +\footnote{The Linux implementation further separates the PCI virtio code +from the specific virtio drivers: these drivers are shared with +the non-PCI implementations (currently lguest and S/390). +} + + Extensible: Virtio PCI devices contain feature bits which are + acknowledged by the guest operating system during device setup. + This allows forwards and backwards compatibility: the device + offers all the features it knows about, and the driver + acknowledges those it understands and wishes to use. + +\section{Terminology}\label{Terminology} + +The key words "must", "must not", "required", "shall", "shall +not", "should", "should not", "recommended", "may", and +"optional" are to be interpreted as +described in \hyperref[intro:rfc2119]{[RFC2119]}. Note that for +reasons of style, these words are not capitalized in this +document. \section{Normative References} \begin{longtable}{l p{5in}} \phantomsection\label{intro:rfc2119}\textbf{[RFC2119]} & S. Bradner, Key words for use in RFCs to Indicate Requirement Levels, \newline\url{http://www.ietf.org/rfc/rfc2119.txt}, March 1997\\ + \phantomsection\label{intro:S390 PoP}\textbf{[S390 PoP]} & z/Architecture Principles of Operation, \newline IBM Publication SA22-7832\\ + \phantomsection\label{intro:S390 Common I/O}\textbf{[S390 Common I/O]} & ESA/390 Common I/O-Device and Self-Description, \newline IBM Publication SA22-7204\\ \end{longtable} \section{Non-Normative References} - - - \newpage -\section{Section} - - -\subsection{Second level heading} -\subsubsection{Third level heading} -\paragraph{Fourth level heading} -\subparagraph{Fifth level heading} - |