本文探讨了sysfs和udev的内部工作机制，解释了/sys/dev和/sys/devices的区别，并详细介绍了如何通过sysfs查找设备和udev的工作流程。
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, 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
---------------------------------------
|KernelObjects
---------------------------------------
|ObjectAttributes
---------------------------------------
|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
Device: 5h/5d
Access: (0660/brw-rw----)
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)
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, 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
---------------------------------------
|KernelObjects
---------------------------------------
|ObjectAttributes
---------------------------------------
|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
Device: 5h/5d
Access: (0660/brw-rw----)
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)
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