Check if USB device is idling, LINUX

Question

I've got a quick question, but I can't find an answer. Is it possible in linux (or in python) to see if an external usb pen drive is idling? I need to know this for a python script I'm writing. I need to rename a folder on an external usb pen drive as soon as nothing is writing to it.

edit: I know there is lsof command to list open files. 'lsof /theDir' only works half. It works OK when the process copying to the USB is still running. But when the process stops, lsof shows nothing. But the OS is still writing to the USB from its buffer.

Answer 1

You can check if all I/O has been processed by having a look at /sys/block/<dev>/stat. The ninth column contains the number of I/Os currently in flight. Check https://www.kernel.org/doc/Documentation/block/stat.txt
Once this numner is zero the device should be idle.

To force all buffers to be written immediately you could execute sync and wait until it returns.

Nevertheless be aware that you have a race condition here if you are not controlling the writing - after you decided that the device is idle some other process could start writing to it.