I have a Lenovo Thinkpad T540p with Windows 10 (to play some games) so I wanted to dual boot it with DragonFly BSD!
I found the following post to chainload DragonFly BSD with GRUB2.
So first a little background. DragonFly BSD comes with a simple installer that works very well if your disk has an MBR partition table, or takes up the entire disk. The kernel is GPT compatible but the bootloader is not (inspection of the boot1 source code reveals it is exclusively MBR based). This need not be a problem if DragonFly is your only system, or you’re happy with MBR and DragonFly’s boot0 bootloader.
The case here is diferent but the bootloader of DFBSD kills the windows loader.
First install Windows 10 then install DragonFly BSD take note of the slice you installed DFBSD, DON’T install boot0 ou bootblocks in the instaler, instead after it finished the installation drop to a shell by going to Live CD Utilities and execute the following command
disklabel64 -B da0s5 (change da0s5 for your slice) to install the bootblocks that will be chainloaded by the Windows Boot Manager.
Install EasyBCD then go to Add Entry, choose Linux/BSD create your entry and point to your partition:
Now you have the following entry in the boot list:
After this when booting windows you will have a menu to choose your operation system. Please note that when chosing DragonFly BSD it will reboot and in next startup load it!
If you have any doubts or questions ping me on freenode #freebsd or efnet #dragonflybsd, nick dKade.