Hi, Since last December me and Oliver are trying to fix a number of problems in usb-serial.c. Most of them happen when devices are plugged and unplugged and files are opened and closed in various orders.
usb-serial.c registers new tty ports by calling device_register from usb_serial_probe routine, which is called when a supported USB device is plugged. Typically, the first such device is registered as ttyUSB0 and ttyUSB1. If another device is plugged at the same time, then it will be registered as ttyUSB2-ttyUSB3, etc. When device is unplugged and all files opened to it's ports are closed, then destroy_serial function is called, which calls device_unregister on each port (like ttyUSB0 and ttyUSB1). When the device is re-plugged, then it will get the same ttyUSB0 and ttyUSB1 again. Unfortunately, it is possible (and common) for a device to be un-plugged and re-plugged while an application still holds file ttyUSB0 opened. Here two solutions are possible: 1. Keep port range (ttyUSB0 and ttyUSB1 in this case) reserved until all files are closed. This is what the current code attempts to do. But this means that if the same device is re-plugged, it will be registered as ttyUSB2,ttyUSB3, even if it is the only connected device. I had seen applications (in embedded solutions), which had ttyUSB0 hardcoded because they expected only single USB peripheral at a time. Such applications will be broken by this approach. 2. Unregister ports in usb_serial_disconnect (by calling device_del). Mark such ports as dead, so all further calls to serial_* routines on these ports will fail (this was already implemented by Oliver's and my patches). Allow newly plugged devices to reuse the same ttyUSB0-ttyUSB1 range. Allow applications to open files to this new device. Allow applications to keep open files to long disappeared devices as long as they want - they will not interfere with new devices and newly opened files. Please, vote on #1 or #2. This is Oliver's opinion: " It seems to me that if we cannot guarantee that the devices are identical, we must make sure they have different numbers. Consider the case of a multithreaded program opening the same device multiple times. However, this is not a question I alone should decide. Please ask the full list. " Thank you John ____________________________________________________________________________________ TV dinner still cooling? Check out "Tonight's Picks" on Yahoo! TV. http://tv.yahoo.com/ ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
