Alan Stern wrote: > > Another way of thinking about it: Suppose an existing device entry was > not removed (or least made inaccessible) when you unplugged the device > -- the idea being that the existing entry could be reused if you > plugged the device back in. Then if you never did plug it back in, the > old entry would hang around indefinitely, using up resources for no > good reason. > > Alan Stern
How about thinking this way: Got a GPS hockey puck plugged into a hub. the ttyUSB0 is created, and the user program sees that there is a ttyUSB0. Application opens ttyUSB0. Application processes data from ttyUSB0. Everybody happy, till someone yanks the USB cord so that the connection is broken. Kernel sees I/O error. Application program sees I/O error. Application program has no idea what happened. 5 seconds later tries to reestablish communications with device ( still gets I/O error ). /dev/ttyUSB0 still alive because the application still has it opened. Now User realises that the cable was unplugged. plugs it back in. Now there is a ttyUSB1, and an effectively a dead ttyUSB0. Even though the user has plugged in the USB device, the application still reports error. Application does not know or understand that the USB device is now connected to ttyUSB1. After some arbitrary while, application thinks the device is dead ( or user has told application so, presuming that user has any idea as to what happened ). Application closes FD channel. Now /dev/ttyUSB0 disappears. User says to application - go open ttyUSB0. Its plugged back in. its the only USB device. ttyUSB0 is not to be found ( under this scenario ). I suppose one can ask about the resources allocated for a file that has been opened, and someone else deletes file. The application still sees the file, but the rest of the world does not. a new file, with same name can be created which wont affect the deleted, but still present file. Once the deleted file is closed, those resources will be returned to their respective pools. Garmin_GPS, the device handler for the hockey puck GPS device, knows that the newly plugged in USB device is inder its wings. Does garmin_gps know that the device has disconnected? It certainly knows when the USB device gets connected. I suppose we can play mix & match for some time with when and how USB devices get connected and assigned /dev/ names. But if you cannot get garmin_gps to reconnect to ttyUSB0 when the device is unplugged ( but not closed) then maybe the special dev should be erased, and the internal names erased. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
