On Mon, 29 Aug 2016, Greg KH wrote: > > >> I have since compiled 4.8.0_rc1. And just as you guys suggested a part > > >> of problem is solved. The minor number now definitely goes up to 512 > > >> before giving no more free serial devices. But it still doesn't reuse > > >> the minors after disconnecting. > > >> > > >> In my code I'm calling modbus_close and modbus_free which in turn call > > >> close() and free() on the file descriptor. Shouldn't this make the > > >> minor reusable? Yes, it should. > > >> >From what i understand minor numbers are allocated and freed by the > > >> driver. So how does the driver know to release the minor number after > > >> the file descriptor is closed? > > > > > > The USB serial driver core code handles this for you automatically after > > > the last reference goes away. Are you sure that userspace is properly > > > releasing the device properly? > > > > > > thanks, > > > > > > greg k-h > > > > >From my understanding it is, but let me double check. If i compile the > > kernel with some print statements in usb-serial.c, will i get the > > output in stdout? > > You can use dynamic debugging on the usb_serial.ko kernel module to see > the open/close messages in the kernel log, along with when minors are > allocated. Read about how to turn that on in the Documentation/ > directory (search for dynamic debugging). The command is: echo module usbserial =p >/sys/kernel/debug/dynamic_debug/control (note that you need to mount a debugfs filesystem on /sys/kernel/debug first). > > In the userspace is it sufficient to just call close() on the file > > descriptor in /dev ? > > Yes. > > > Is it possible that udev has already replaced /dev/ttyUSBx with > > /dev/ttyUSBx+1 by the time the program calls close() on it? > > Yes, if it is open. And udev does not create the device node, the > kernel is doing so. > > If your program/device does the following: > - userspace open ttyUSB0 > - device disconnect > - device connect (ttyUSB1) > - userspace close ttyUSB0 > - kernel removes ttyUSB0 > > that could be what is happening here, you are racing and loosing :( But even in this case, the kernel would re-use the old minor numbers once the ttyUSB files had been closed. 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
