关于sys/device和/dev的区别

sysfs introduction:

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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.

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|Internal 
           |External     |

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|KernelObjects      | Directories   |

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|ObjectAttributes    |Regular Files |

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|Object Relationships | Symbolic Links|

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

/sys/dev:

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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 file system representation of the device tree. It maps directly to the internal kernel device tree, which is a hierarchy of struct device.

udev:

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udev is a device management 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 informs the udevd daemon when certain events happen. The udevd daemon is configured torespond
to some events with actions. Always, it means adding/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 rules against the available

device attributes provided in sysfs

* If a match is found, one or more actions (e.g., create device node, 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)