【Xen】什么是 Xen Hypervisor

What is Xen Hypervisor?

 

什么是Xen Hypervisor?

The Xen hypervisor is a layer of software running directly on computer hardware replacing the operating system thereby allowing the computer hardware to run multiple guest operating systems concurrently. Support for x86, x86-64, Itanium, Power PC, and ARM processors allow the Xen hypervisor to run on a wide variety of computing devices and currently supports Linux, NetBSD, FreeBSD, Solaris, Windows, and other common operating systems as guests running on the hypervisor.

Xen Hypervisor 是一套直接运行在计算机硬件之上的软件层，它代替操作系统，从而允许计算机硬件能同时运行多个客户操作系统。Xen Hypervisor 支持X86、X86-64、Itanium、Power PC和ARM处理器，使得它能广泛地应用在各种计算设备上，并且支持Linux、NetBSD、FreeBSD、Solaris、Windows和其它常用的操作系统作为它的客户操作系统在其上运行。

 

The Xen.org community develops and maintains the Xen hypervisor as a free solution licensed under the GNU General Public License.

 

Xen.org社区开发和维护Xen hypervisor，作为一个免费的解决方案，它基于GNU GPL版权。

 

A computer running the Xen hypervisor contains three components:
• Xen Hypervisor
• Domain 0, the Privileged Domain (Dom0) – Privileged guest running on the hypervisor with direct hardware access and guest management responsibilities
• Multiple DomainU, Unprivileged Domain Guests (DomU) – Unprivileged guests running on the hypervisor; they have no direct access to hardware (e.g. memory, disk, etc.)

 

一个运行Xen hypervisor的计算机系统包含三个组件：

• Xen hypervisor自身

• 0域，特权域 -- 在Xen hypervisor上运行的特权用户，负责管理其它客户操作系统，并且能直接访问硬件资源

• 多个U域，非特权域用户 -- 在Xen hypervisor上运行的非特权用户，不能直接访问硬件资源

 

The Xen hypervisor runs directly on the hardware and becomes the interface for all hardware requests such as CPU, I/O, and disk for the guest operating systems.  By separating the guests from the hardware, the Xen hypervisor is able to run multiple operating systems securely and independently.

Xen hypervisor直接运行在硬件层之上，并且为所有硬件请求的提供接口功能，例如客户操作系统的CPU请求，I/O请求，磁盘请求等。通过分离客户操作系统和硬件层，Xen hypervisor能同时安全并独立地运行多个操作系统。

 

The Domain 0 Guest referred to as Dom0 is launched by the Xen hypervisor during initial system start-up and can run any operating system except Windows.  The Dom0 has unique privileges to access the Xen hypervisor that is not allocated to any other Domain Guests. These privileges allow it to manage all aspects of Domain Guests such as starting, stopping, I/O requests, etc. A system administrator can log into Dom0 and manage the entire computer system.

 

被称为Dom0的0域用户，是被Xen hypervisor在系统引导过程中启动的，它能运行出了Windows以外的任何操作系统。Dom0被赋予独一无二的权限去访问Xen hypervisor，这是其它域用户所没有的。这些权限允许它去管理域用户的方方面面，包括启动，停止，I/O请求等。系统管理员可以登录到Dom0去管理这个计算机系统。

 
The Domain Guests referred to as DomUs are launched and controlled by the Dom0 and
independently operate on the system. These guests are either run with a special modified operating system referred to as paravirtualizion or un-modified operating systems leveraging special virtualization hardware (Intel VT and AMD-V)  referred to as hardware virtual machine (HVM).  Note – Microsoft Windows requires a HVM Guest environment.

 

DomU有Dom0启动并控制，然后独立地运行在系统中。这些用户可以以特定的修改过的操作系统的方式运行（常被称为准虚拟化），也可以借助特殊的虚拟化硬件运行完全没有修改过的操作系统，这种特殊的虚拟硬件常被称为硬件虚拟机，使用了Intel VT或AMD-V的技术。注意，Windows操作系统需要硬件虚拟机客户环境。

 

• Paravirtualization   
A term used to describe a virtualization technique that allows the operating system to be aware that it is running on a hypervisor instead of base hardware. The operating system must be modified to accommodate the unique situation of running on a hypervisor instead of basic hardware.

 

• 准虚拟化

用来描述一种虚拟化技术的术语，这种虚拟化技术要求当客户操作系统运行在hypervisor 上时，要进行修改以适应hypervisor对系统要求。

• Hardware Virtual Machine (HVM)   
A term used to describe an operating system that is running in a virtualized environment unchanged and unaware that it is not running directly on the hardware. Special hardware is required to allow this, thus the term HVM.

 

• 硬件虚拟机

操作系统运行在虚拟环境中，无须修改和关心它是否直接运行在硬件之上。