Bark woof bark. So cute!
If you want the mmapi dev package pre-installed on the rootfs, that’s more complicated. Using SDKM for that is the easiest way (if it does that). Alternatively, you can use a chroot script to enter the rootfs and install the package from the online apt repos as you would with a live system. You’ll need to make a slight change to the apt sources first. To do all that:
First sudo apt install qemu-user-static on your Ubuntu desktop machine.
Second, edit <SOC> out of Linux_for_Tegra/rootfs/etc/apt/sources.list.d/nvidia-l4t-apt-source.list so it looks like this for Nano:
deb https://repo.download.nvidia.com/jetson/common r32.4 main
deb https://repo.download.nvidia.com/jetson/t210 r32.4 main
Third, download and run the above linked script to enter the rootfs as shown in the linked post. From within the chroot, run apt-get update (no sudo) and then if that works, install the multimedia api samples as you usually would. Just type exit when you’re done to unmount the special filesystems. You can install other packages if you wish (even third party, or your own). sudo is not needed since you’re already root and may cause odd warnings if it is used.
I have not specifically tested it with flash.sh, or nvmassflashgen, however they should work as expected with the modified rootfs. You can check the full docs here, which is where the above thread’s instructions are derived from. The chroot technique is borrowed from Nvidia’s scripts (it’s how the debian packages are installed, which you can also do).