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分类: LINUX
2014-09-05 10:11:22
一直没有认真看过sysfs的文档,所以一直就迷迷糊糊的不知道/sys/dev和/sys/devices到底啥关系,另外对于udev也是一知半解。懒啊...
终于遇到了问题,不得不看看文档,总结了下:
sysfs introduction:
----------------------------
sysfs is a mechanism for representing kernel objects, their attributes, and their relationships
with each other.
It provides two components: a kernel programming interface for exporting these items via sysfs, and a user interface to view and manipulate these items that maps back to the kernel objects which they represent.
The table below shows the mapping between internel (kernel) constructs and their external
(userspace) sysfs mappings.
---------------------------------------
|Internal | External |
---------------------------------------
|Kernel Objects | Directories |
---------------------------------------
|Object Attributes | Regular Files |
---------------------------------------
|Object Relationships | Symbolic Links|
---------------------------------------
(Reference: )
/sys/dev:
------------------
Contains two directories char/ and block/. Inside these two directories there are symlinks named
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 special file
Device: 5h/5d Inode: 5484 Links: 1 Device type: 8,1
Access: (0660/brw-rw----) Uid: ( 0/ root) Gid: ( 6/ disk)
Access: 2011-08-24 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 maps directly to the internal kernel device tree, which is a hierarchy of struct device.
udev:
-----------------------------
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 to respond 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)