1. /*
* if a resource is "BUSY", it's not a hardware resource
* but a driver mapping of such a resource; we don't want
* to warn for those; some drivers legitimately map only
* partial hardware resources. (example: vesafb)
*/
if (p->flags & IORESOURCE_BUSY)
所以pci resource 分为硬件资源 猜想就是映射的是物理地址， 软件资源应该就是映射的是物理内存，带到后面验证吧。
2.这里使用了读写锁， 没有深入，大概是可以很多读的互斥写操作的锁，据说是初始一个很大的信号量a，然后读操作-1， check是否是大于0， 写操作-a，check是否等于0来实现互斥。
3.假设我要对某外设的IO资源进行保护。防止用户空间訪问。能够将其resource的flags置位exclusive就可以。？？
4.0x10000 65536 各端口， 但是在64位机器中，端口资源会更多，所以不会再resource中限制，具体情况在acpi中
/*
* The legacy I/O space defined by the ia64 architecture supports only 65536 ports, but
* large machines may have multiple other I/O spaces so we can't place any a priori limit
* on IO_SPACE_LIMIT. These additional spaces are described in ACPI.
*/
5.e820 :ttp://blog.csdn.net/chenyu105/article/details/49892265