The files in /dev are actual devices files which UDEV creates at run time. The directory /sys/class is exported by the kernel at run time, exposing the hierarchy of the hardware through sysfs.

/dev下的文件是真实的设备,由UDEV在运行时创建。
/sys/class 则是由kernel在运行时导出的,目的是通过文件系统暴露出硬件的层级关系。