在我的 linux 机器上（uname -a Linux gate 3.2.0-0.bpo.2-amd64 #1 SMP Fri Jun 29 20:42:29 UTC 2012 x86_64 GNU/Linux）我有 USB 调制解调器 WeTelecom WM-D300有“zeroCD”选项。ZeroCD USB id 为 22de:6803，调制解调器设备的 USB id 为 22de:6801。我已经为它创建了 usb_modeswitch 规则并测试了这个规则运行良好：
Aug 11 23:03:14 gate kernel: [ 609.832373] usb 1-1: usbfs: process 6081 (usb_modeswitch) did not claim interface 0 before use
Aug 11 23:03:14 gate kernel: [ 609.949352] usb 1-1: USB disconnect, device number 2
Aug 11 23:03:15 gate kernel: [ 610.596344] usb 1-1: new high-speed USB device number 5 using ehci_hcd
Aug 11 23:03:15 gate kernel: [ 610.759964] usb 1-1: New USB device found, idVendor=22de, idProduct=6801
Aug 11 23:03:15 gate kernel: [ 610.759978] usb 1-1: New USB device strings: Mfr=3, Product=2, SerialNumber=0
Aug 11 23:03:15 gate kernel: [ 610.759987] usb 1-1: Product: Wetelecom Mobile Products
Aug 11 23:03:15 gate kernel: [ 610.759994] usb 1-1: Manufacturer: WeTelecom Incorporated
Aug 11 23:03:16 gate kernel: [ 611.820404] option 1-1:1.0: GSM modem (1-port) converter detected
Aug 11 23:03:16 gate kernel: [ 611.820760] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB3
Aug 11 23:03:16 gate kernel: [ 611.820876] option 1-1:1.1: GSM modem (1-port) converter detected
Aug 11 23:03:16 gate kernel: [ 611.821095] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB4
Aug 11 23:03:16 gate kernel: [ 611.821204] option 1-1:1.2: GSM modem (1-port) converter detected
Aug 11 23:03:16 gate kernel: [ 611.821418] usb 1-1: GSM modem (1-port) converter now attached to ttyUSB5
所以，我做了一个小的 udev 配置来允许这个设备的自动热插拔：
ACTION!="add|change", GOTO="modem_rules_end"
SUBSYSTEM!="usb", GOTO="modem_rules_end"
LABEL="modem_rules_begin"
# WeTelecom WM-D300
ATTRS{idVendor}=="22de", ATTRS{idProduct}=="6803", RUN+="usb_modeswitch '%b/%k'"
LABEL="modem_rules_end"
它不工作。重新连接调制解调器后，它变得完全不可用。usb-devices 显示它具有 usbfs 驱动程序，并且 usb_modeswitch 即使从命令行也无法切换它。udev 也无法切换，但重新启动后它工作得很好 - 直到下一次物理重新连接。这是我插入调制解调器时的 udev 日志：
Aug 11 22:42:11 gate logger: usb_modeswitch: using overriding config file /etc/usb_modeswitch.d/22de:6803; make sure this is intended
Aug 11 22:42:11 gate logger: usb_modeswitch: please report any new or corrected settings; otherwise, check for outdated files
Aug 11 22:42:11 gate logger: usb_modeswitch: using overriding config file /etc/usb_modeswitch.d/22de:6803; make sure this is intended
Aug 11 22:42:11 gate logger: usb_modeswitch: please report any new or corrected settings; otherwise, check for outdated files
Aug 11 22:42:11 gate usb_modeswitch: switching device 22de:6803 on 001/006
Aug 11 22:42:11 gate usb_modeswitch: switching device 22de:6803 on 001/006
Aug 11 22:42:11 gate kernel: [ 1495.864235] usb 1-1: usbfs: process 8485 (usb_modeswitch) did not claim interface 0 before use
Aug 11 22:42:11 gate kernel: [ 1495.864309] usb 1-1: usbfs: process 8485 (usb_modeswitch) did not claim interface 0 before use
Aug 11 22:42:16 gate logger: usb_modeswitch: switched to 22de:6803 on 001/006
Aug 11 22:42:19 gate logger: usb_modeswitch: switched to 22de:6803 on 001/006
所以，我的问题是：为什么以及如何？为什么它从命令行工作以及如何通过 udev 使其工作？请帮忙。提前谢谢！