[coreboot] cbfstool and initrd.cpio.xz

[Trammell Hudson]

I was having a problem with adding compressed initrd images to my Linux 
payload with cbfstool.  What I noticed is that if I build my initrd.cpio 
file and compress/link it into the bzImage via the Linux kernel's 
.config file, the kernel starts up just fine and executes out of the 
initrd.  Likewise, if I have the coreboot .config bundle the bzImage and 
an uncompressed initrd.cpio, then it also works, but produces an image 
much too large for a real system.  However, trying to have cbfstool 
bundle initrd.cpio.xz would cause the kernel to panic.

Digging through the Linux kernel build scripts, I found that 
linux/scripts/gen_initramfs_list.sh passes in some extra options to 
compress the initrd.cpio file before linking it in.  These options are 
necessary for the kernel to be able to decompress the xz file:

        xz \
                --check=crc32 \
                --lzma2=dict=1MiB \
                --extreme \
                < "$<" \
                > "$@"

-- 
Trammell