Booting Linux minimally

I am trying to boot just linux itself. It’s mostly for the learning experience.
I got a small HDD with only one ext4 partition looking like this:

/bin/bash             
/dev/console
/boot/vmlinuz         
/boot/grub/grub.cfg
/boot/grub/i386-pc/*.mod

bash is version 3.0 statically linked, vmlinuz is version 3.16.2, and grub is version 2.00rc1. grub.cfg looks like this:

insmod linux
insmod search 
insmod ext2
insmod part_msdos
set timeout=5

menuentry 'Linux' {
    set the_root_uuid=a0225737-71c9-4d60-81e2-275dc078c3c1
    search --fs-uuid $the_root_uuid --set=root
    linux /boot/vmlinuz root=$root ro init=/bin/bash
}

when booting I get the following:

kernel panic: VFS could not open device root (hd0,msdos1), or unknown block(0,0) error -6

What am I missing?