Assume raw format for image

[mrtwnklr]

This change fixes the following warning when starting a container:

WARNING: Image format was not specified for '/sdcard/filesystem.img' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.

[lukechilds]

Is it a good idea to hardcode to the raw format over letting QEMU do probing?

If someone has an image in a different format then it won't be able to boot if we hardcode to raw.

Or is raw pretty much ubiquitous for Pi images?

// CC @JamesReynolds

[JamesReynolds]

@lukechilds I have never seen a qcow2 or vmdk image of a raspberry pi disk, I'm sure that raw is ubiquitous. However, adding ".img" is fairly ubiquitous too, so making ".img" default to raw could be a reasonable compromise?

[lukechilds]

That's a good idea.

@mrtwnklr are you able to check for the .img extension first? If there is an .img extension specify the raw format, if no .img extension just let QEMU do it's probing.

[mrtwnklr]

Yes, that's a good idea.
But checking for the real extension (container-outside) of the volume mounted path is not possible. One could define an additional env var IS_RAW_IMAGE and use this in entrypoint.sh to prevent the warning.

[lukechilds]

Oh of course, .img is hardcoded in the entrypoint. In that case I don't think the check is necessary. By requiring a .img file I guess we are implicitly saying we expect the raw format.

[lukechilds]

@mrtwnklr are you able to just rebase this on top of the latest changes and then this is good to be merged. Thanks!

[mrtwnklr]

Ok, that's it.

[lukechilds]

Thanks @mrtwnklr!