为什么Xen这么难

    最为直接的一个原因是在OS上加上一层抽象，多一层抽象就多了一坨恶心的东西。个人资质不够，相关资料少也可以做为理由。另外有Dom 0和Dom U之分，还有用户态和guest OS的交互，都让人发晕。
    自身曾花很长时间弄懂了一个xenstore的问题,曾到xen-devel发过帖子
[Xen-devel] question about relationship between /var/lib/xenstored/tdb and xenstore_domain_interface
Date: Sun, 23 Oct 2011 17:13:41 +0800
Hi, when I read following link, , then I browsed some Xen 3.1 code. A question puzzles me. As we know "The physical xenstore resides in one file: /var/lib/xenstored/tdb. " , but drives(frontend/backend) visit Xenstore by Xenbus. The data structure manipulated by Xenbus is xenstore_domain_interface, not tdb. while tdb file is visited by Xenstored daemon. I cann't figure out the relationship between tdb and xenstore_domain_interface. For example, if Xenbus sends a XS_DIRECTORY query message , where does the reply message come from? 回贴并没有给我直接答案，我还跑到qq群问过，后来过年这个问题就放下了。我发出过这样的感叹：
VM,why are you so virtual to me?

上周我把ACM训练的事情放一下重回XEN时，我又想到了这个问题，终于解决了，然后一鼓作气整理几个xen的文档。

“二句三年得，一吟双泪流”。其实，贾岛应该高兴才对，这种体验不是什么人都会有。