/sys/dev 和/sys/devices 和udev的关系

sysfs introduction:
----------------------------
sysfs is a mechanism for representing kernel objects, theirattributes, and their relationships
with each other.

It provides two components: a kernel programming interface forexporting these items via sysfs, and a user interface to view andmanipulate these items that maps back to the kernel objects whichthey represent.

The table below shows the mapping between internel (kernel)constructs and their external
(userspace) sysfs mappings.
---------------------------------------
|Internal                        |External          |
---------------------------------------
|KernelObjects            | Directories     |
---------------------------------------
|ObjectAttributes       |Regular Files |
---------------------------------------
|Object Relationships | Symbolic Links|
---------------------------------------
(Reference:http://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf)

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

Example:
root@AuxLinux:/sys# ls -l dev/block/ 8:1
lrwxrwxrwx 1 root root 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 specialfile
Device: 5h/5d     Inode:5484              Links:1        Devicetype: 8,1
Access: (0660/brw-rw----)   Uid:(      0/      root)     Gid:(      6/      disk)
Access: 2011-08-24 18:25:02.902025252 +0800
Modify: 2011-08-18 15:14:17.281472005 +0800
Change: 2011-08-18 15:14:17.281472005 +0800

/sys/devices:
----------------------------
Contains a filesystem representation of the device tree. It mapsdirectly to the internal kernel device tree, which is a hierarchyof struct device.

udev:
-----------------------------
udev is a device management framework that replaced the devfsfacility in the Linux 2.6 kernel. It is composed of some kernelservices and the udevd daemon. The kernel informs the udevd daemonwhen certain events happen. The udevd daemon is configured torespond to some events with actions. Always, it meansadding/removing device file under /dev dynamically.

* When the kernel detects that a device has been added or removed,a uevent is sent to
the udevd daemon through a netlink socket
* When udevd receives the uevent, it matches its configured rulesagainst the available
device attributes provided in sysfs
* If a match is found, one or more actions (e.g., create devicenode, remove device node,
install firmware, etc.) are taken

(Usage Reference:http://www.ibm.com/developerworks/cn/linux/l-cn-udev/index.html?ca=drs-cn-0304)

转载：http://blog.csdn.net/xuesen_lin/article/details/6946719