Cloudow:一种基于用户层虚拟化的软件即服务模式运行系统

Cloudow:A SaaS runtime system based on the user-level virtualization technology

"软件即服务(SaaS)"是一种通过网络发布与使用软件的新模式,在很大程度上消除了用户购买、维护与升级应用程序的需要,被认为是软件未来的主流应用模式之一.本文提出了一种新的支持现有Windows桌面软件的SaaS模式并实现了其原型系统Cloudow:用户可以在任意的联网兼容计算机上按需运行现有的Windows软件(无需安装),且软件的个性化配置可以被保留以便下次使用时恢复.Cloudow使用用户层虚拟化技术解决了软件无需安装便能运行的问题,并通过用户层文件系统设计实现了软件在网络环境下的透明使用.与现有的基于远程虚拟机计算或者基于Web应用的SaaS模式相比,Cloudow能够直接支持现有软件的服务端存储/客户端运行模式,无需修改代码,较好地兼顾了软件兼容性与性能.同时,为尽可能降低Internet环境所带来的远程数据访问延迟,Cloudow大量采用了元数据/数据/文件预取与缓存策略,显著提高了实际部署中的应用性能;测试表明,因为采用了这些优化策略,对于很多常用的Windows桌面应用而言,在Cloudow下额外运行时间开销平均为12%到20%.

SaaS is a promising mode for software delivery and usage across the Internet,which eliminates the need of users to purchase,maintain and upgrade software to a large extent.This paper proposes a new SaaS mode for legacy Windows software and its prototype,Cloudow.Cloudow enables ordinary users of Windows PC to use legacy desktop software from the Internet without installation,and the system supports to restore the user’s personal software configurations on another PC.User-level virtualization technology is employed to enable legacy software to run without installation.Moreover,an on-demand delivery method based on the user-space file system is adopted,so the user can launching the remote software just as launching the local counterpart. Compared with the existing SaaS modes（like the VM-based solution and the Web applications）,the legacy software can run on the client end directly while stored on the remote site,which gets good balance between compatibility and performance.Furthermore,aggressive pre-fetch mechanisms（including metadata/data/file pre-fetch）and caching technologies are employed to improve the IO access performance remarkably.The tests show that for much common software,the runtime overhead is about 12%–20%.