[U-Boot] user-space ===>> U-Boot ====>> user-space ?

Hi Is there a simple way to send data from a Linux user-space program to U-Boot? How about from U-Boot up to a user-space program?

The data may change often enough that using fw_printenv and fw_setenv might wear out the NAND storage area for the environment.

The use-case is to have two kernel images, two root file systems, and to let a user-space application specify which to use and then force a reboot. The system will not lose power during this reboot.

This seems like a common enough problem. Has anyone solved it before?