OS Development. Creating bootable iso from files.

Question

I'm studying OS development and I use brokenthorn resource but with a little bit different tool, namely, I use CentOS, NASM and Qemu as a test/dev environment. I've been facing some issues while creating bootable img file with secondary loader.

I've got two files: 1. bootloader.bin which is first stage loader. 2. stage2.bin which is secondary loader.

In order to create bootable img file I do the following:

• dd if=/dev/zero of=floppy.iso bs=1024 count=1440 -- Creating empty file
• mkfs.vfat -F 12 floppy.iso --Creating file system in the file
• dd if=../bin/bootloader.bin of=floppy.iso bs=512 count=1 conv=notrunc --Writing first loader to the boot sector
• sudo mount -o loop floppy.iso /mnt/floppy/ -- Try to mount file system to write secondary loader using previously create FAT-12 files system.

In the last step I'm getting the following error:

mount: /dev/loop0 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

Can you please help me to understand what I'm doing wrong and what other ways I can use to accomplish creating bootable img with file system on board. Thanks!

Answer 1

I once stumbled upon the similar problem and this answer may be of help to you.

However I would strongly recommend you switching to bootloader like Grub and spend time and effort developing the actual OS of yours. For that I would reccomend grub resque as it's simple to use and allows to to quickly create ISO that you can either burn or feed to virtual machine. Otherwise, you may just drown in all these minor things like enabling protected mode, loading your stages and so on.