[coreboot] using overlayfs to have several coreboot dev envs

[Trammell Hudson]

On Sun, Nov 13, 2016 at 03:34:49PM -0500, Charlotte Plusplus wrote:
> With the cross compiling tool chain, coreboot takes 1G. If you are a bit
> short on space, or if you want to save writes to your SSD, instead of
> having multiple copies of the coreboot source folder, I have found out
> overlayfs is very practical. [...]

An alternative is to use the "external build" option if you're building
for multiple targets with different .config files for each.  It isn't
quite as simple as the Linux kernel's kbuild O= syntax, but works
fairly well.

I have three main builds that I'm alternating between (x230, chell and qemu)
so I've created three directories and have a .config for each stored in
a top-level config directory.  From the coreboot directory I can modify
the configs and build them independently:

	make obj=./x230 DOTCONFIG=./config/x230 menuconfig
	make obj=./x230 DOTCONFIG=./config/x230 -j 8

The builds will share the same cross build tree, so the actual build
output is only 64M per configuration.

Also note that any paths to external files like bzImage and initrd in
each buld's .config are relative to the coreboot tree, not the output
directory.

-- 
Trammell