/dev，設(shè)備文件存儲目錄，應(yīng)用程序通過對這些文件的讀寫和控制，可以訪問實際的設(shè)備；

/sys/devices目錄，按照設(shè)備掛接的總線類型，組織成層次結(jié)構(gòu)，保存了系統(tǒng)所有的設(shè)備；是文件系統(tǒng)管理設(shè)備的最重要的目錄結(jié)構(gòu)；

這是內(nèi)核設(shè)備按總線類型分層放置的目錄結(jié)構(gòu)， devices 中的所有設(shè)備都是連接于某種總線之下，在這里的每一種具體總線之下可以

找到每一個具體設(shè)備的符號鏈接，它也是構(gòu)成 Linux 統(tǒng)一設(shè)備模型的一部分；

/sys/dev下有兩個子目錄，block和char，存放的是塊設(shè)備和字符設(shè)備的主次號碼，形式為(major:minor)，它指向/sys/devices目錄下的

設(shè)備。

一直沒有認真看過sysfs的文檔，所以一直就迷迷糊糊的不知道/sys/dev和/sys/devices到底啥關(guān)系，另外對于udev也是一知半解。懶啊...

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終于遇到了問題，不得不看看文檔，總結(jié)了下：

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sysfsintroduction:

----------------------------

sysfs is amechanism for representing kernel objects, their attributes, and theirrelationships

with each other.

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It provides twocomponents: a kernel programming interface for exporting these items via sysfs,and a user interface to view and manipulate these items that maps back to thekernel objects which they represent.

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The table belowshows the mapping between internel (kernel) constructs and their external

(userspace) sysfsmappings.

---------------------------------------

|Internal???????????? | External????? |

---------------------------------------

|KernelObjects?????? | Directories?? |

---------------------------------------

|ObjectAttributes??? | Regular Files |

---------------------------------------

|ObjectRelationships | Symbolic Links|

---------------------------------------

(Reference:http://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf)

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/sys/dev:

------------------

Contains twodirectories char/ and block/. Inside these two directories there are symlinksnamed <major>:<minor>. These symlinks point to the sysfs directoryfor the given device. /sys/dev provides a quick way to lookup the sysfsinterface for a device from the result of a stat(2) operation.

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Example:

root@AuxLinux:/sys#ls -l dev/block/8:1

lrwxrwxrwx 1 rootroot 0 2011-08-26 10:13 dev/block/8:1 ->../../devices/pci0000:00/0000:00:10.0/host2/target2:0:0/2:0:0:0/block/sda/sda1

root@AuxLinux:/sys#stat /dev/sda1

? File: `/dev/sda1'

? Size: 0?????????????? Blocks: 0????????? IO Block: 4096?? block special file

Device: 5h/5d?? Inode: 5484??????? Links: 1???? Device type: 8,1

Access:(0660/brw-rw----)? Uid: (??? 0/???root)?? Gid: (??? 6/???disk)

Access: 2011-08-2418:25:02.902025252 +0800

Modify: 2011-08-1815:14:17.281472005 +0800

Change: 2011-08-1815:14:17.281472005 +0800

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/sys/devices:

----------------------------

Contains afilesystem representation of the device tree. It maps directly to the internalkernel device tree, which is a hierarchy of struct device.

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udev:

-----------------------------

udev is a devicemanagement framework that replaced the devfs facility in the Linux 2.6 kernel.It is composed of some kernel services and the udevd daemon. The kernel informsthe udevd daemon when certain events happen. The udevd daemon is configured torespond to some events with actions. Always, it means adding/removing devicefile under /dev dynamically.

總結(jié)

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