《Linux内核修炼之道》精华分享与讨论（6）——分析内核源码如何入手？（上）
作者 佚名技术
来源 Linux系统
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发布时间 2012-04-23
| 选项.
15 config USB_DEVICEFS 16 bool "USB device filesystem" 17 depends on USB 18 ---help--- 19 If you say Y here (and to "/proc file system support" in the "File 20 systems" section, above), you will get a file /proc/bus/usb/devices 21 which lists the devices currently connected to your USB bus or 22 busses, and for every connected device a file named 23 "/proc/bus/usb/xxx/yyy", where xxx is the bus number and yyy the 24 device number; the latter files can be used by user space programs 25 to talk directly to the device. These files are "virtual", meaning 26 they are generated on the fly and not stored on the hard drive. 27 28 You may need to mount the usbfs file system to see the files, use 29 mount -t usbfs none /proc/bus/usb 30 31 For the format of the various /proc/bus/usb/ files, please read 32 <file:Documentation/usb/proc_usb_info.txt>. 33 34 Usbfs files can''t handle Access Control Lists (ACL), which are the 35 default way to grant access to USB devices for untrusted users of a 36 desktop system. The usbfs functionality is replaced by real 37 device-nodes managed by udev. These nodes live in /dev/bus/usb and 38 are used by libusb. 选项USB_DEVICEFS与usbfs文件系统有关.usbfs文件系统挂载在/proc/bus/usb目录,显示了当前连接的所有USB设备及总线的各种信息,每个连接的USB设备在其中都会有一个对应的文件进行描述.比如文件/proc/bus/usb/xxx/yyy,xxx表示总线的序号,yyy表示设备所在总线的地址.不过不能够依赖它们来稳定地访问设备,  同一设备两次连接对应的描述文件可能会不同,比如,第一次连接一个设备时,它可能是002/027,一段时间后再次连接,它可能就已经改变为002/048.
就好比好不容易你暗恋的mm今天见你的时候对你抛了个媚眼,你心花怒放,赶快去买了100块彩票庆祝,到第二天再见到她的时候,她对你说你是谁啊,你悲痛欲绝的刮开那100块彩票,上面清一色的谢谢你.
usbfs文件系统并不属于USB子系统实现的核心部分,与之相关的代码我们可以不必关注.
74 config USB_SUSPEND75 bool "USB selective suspend/resume and wakeup (EXPERIMENTAL)" 76 depends on USB && PM && EXPERIMENTAL 77 help 78 If you say Y here, you can use driver calls or the sysfs 79 "power/state" file to suspend or resume individual USB 80 peripherals. 81 82 Also, USB "remote wakeup" signaling is supported, whereby some 83 USB devices (like keyboards and network adapters) can wake up 84 their parent hub. That wakeup cascades up the USB tree, and 85 could wake the system from states like suspend-to-RAM. 86 87 If you are unsure about this, say N here. 这一项是有关USB设备的挂起和恢复.开发USB的人都是节电节能的好孩子,  协议里就规定了,所有的设备都 支持挂起状态,就是说为了达到节电的目的,当设备在指定的时间内,如果没有发生总线传输,就要进入挂起 |
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