1. grub/grub2 -> https://www.dedoimedo.com/computers/grub-2.html
It is a readable essay, plain words with detail examples, especially for those who want to have several OS in his host.
2. QEMU internal -> http://blog.vmsplice.net/2016/01/qemu-internals-how-guest-physical-ram.html
Actually, there are other good blogs except QEMU, like GIT, Kernel, Linux and so on.
3.How to write a .spec for rpm build: http://ftp.rpm.org/max-rpm/s1-rpm-build-creating-spec-file.html