While modifying the SCH-i909 ROM, I extracted the firmware and found weird .rfs files instead of the usual .img files. What is this?

Google unfortunately had no answer. Moreover, I could NOT, for the life of me, figure out how to create an .rfs file for the new firmware. Until I discovered this tutorial on XDA.

Step 1: Create a temporary directory.

mkdir temp

Step 2: Mount the .rfs file itself.

sudo mount -o loop <filename>.rfs temp/

Step 3: Profit.

I still haven’t managed out how to create these .rfs files, but this is a good workaround.

To unmount after changes have been made, issue:

sudo umount temp/