We're discussing anything that can do open(), read, write(), provides files and directories. Do you understand that virtual filesystems do not have problems with inode counts?

Dupping a directory means a) hw state is saved on open(), in which case you're holding it unnecessary because read() simply may not happen b) hw state is saved on first read(). OK, what to do with parallel dumpers? How to determine when transaction starts and ends? What to do if dumper process is sigkilled?

ioctl(HW_GET_STATE) doesn't have these problems, kernel knows how to kill process inside itself.

Try to save /sys/class/net/lo/* coherently and write down all assumptions which you did.