passthroughfs example does not truncate a file if it is already opened

[pmvr]

For example, if there exists a nonempty file in the mounted directory which is opened (for example) for reading and then again (by a different process) for read/write with the truncate flag, i.e.
os.open(FILENAME, os.O_RDWR | os.O_TRUNC)
it is not truncated.

This is because the inode exists in self._inode_fd_map and os.open with the new flags is not executed by the open method.

[Nikratio]

Thanks for the report! It's difficult to get the right balance between this example being fully correct, and it being simple enough to serve as an introduction. So I'm not sure if it's better to fix this, or to add it to the list of "known bugs" at the top of the file.

[pmvr]

I agree.
I did not propose a fix, because I am afraid that there a some more refined scenarios that would fail.
And instead of just passing through every file open/create request to os.open, which could be an easy fix, it is nice to see and learn from the idea to manage open file handles internally.
Kind regards, Matthias