There are several options for using a second image filesystem:
You can have a readable flash/PROM device that's directly accessible
and has a unique memory address (e.g. flash at 0xD0000000).
Note:
You can't use this flash device for an image filesystem
and a flash filesystem (devf-*) at the same time.
After booting the kernel, you can dynamically map contiguous RAM
(mmap_device_memory()).
Get the physical pointer to this memory, copy an image filesystem to it,
and then mount the ifs.
At boot time (in startup code), copy an area of flash that contains
a prebuilt image filesystem in to a known area of reserved memory.
Mount the second IFS after the kernel has booted.
In this technical note, we'll use the third option.