On Fri, 20 Apr 2012, Greg KH wrote: > > Make the question precise. > > I assme there are two usb ports in my notebook at left and right separately. > > When I plug mouse into > > left usb port, I get 2-1.1:1.0 > > right usb port, I get 2-1.2:1.0 > > > > I want to know whether it is right that no matter how many times I reboot the machine, > > Not always. > > > the test result above will be the same.And if it will be the same, then why it will be the same. > > You got lucky :) > > USB ports on a hub are all enumerated the same, but the root hubs > aren't, and sometimes hubs on the same bus are not as well. > > But usually, things do come up in the same way all the time, so > depending on your use case, you can rely on this, but it is recommended > that you look for something else a bit more unique, like a serial number > on a device (if it is present), if you wish to uniquely identify a > device all the time. In this particular case, it is guaranteed that the left USB port will always be numbered as X-1.1:1.0 and the right port as X-1.2:1.0, where the number X may change from one boot to another. But the -1.1:1.0 and -1.2:1.0 parts will always be the same. This is because X is the bus number, which is allowed to change. The -1.1:1.0 and -1.2:1.0 values are port, configuration, and interface numbers. They will never change, because they come from the hardware. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
