Kernel: Implement virtio-blk driver.

[nichtverstehen]

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[ADKaster]

These definitions look very similar to those from the Linux UAPI.

https://elixir.bootlin.com/linux/v6.9/source/include/uapi/linux/virtio_blk.h
https://github.com/qemu/qemu/blob/9360070196789cc8b9404b2efaf319384e64b107/include/standard-headers/linux/virtio_blk.h

Which is fine because the header explicit says it's licensed as BSD 3-clause so that other projects can implement drivers, but those headers are third-party and need their license intact if we are going to goink them.

Can you:

1. Move these definitions into a Defintions.h with the license comment header reproduced in full
2. Add an exception for that file in our check-license-headers linter script
3. Change the struct names to follow our style? (i.e. PascalCase rather than snake_case)

[spholz]

Those definitions look like they probably are just from the virtio spec.
I'm not sure under what license the spec code snippets are though.

[nichtverstehen]

Thanks for the review!

The definitions are in fact not copied from any other project. I didn't look at the Linux kernel implementation at all and did not copy QEMU definitions (although did look at them).

The definitions come directly from the spec here:
https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-2740002
Added a reference to the spec.

I am not 100% sure that we don't need to add the copyright notice of the spec authors (belonging to OASIS Open). But neither QEMU not Linux kernel reference OASIS copyright. So I guess, that's fine?..

Now about the names. I strived to keep modifications to the definitions from the spec to the minimum. I felt like it would be unnecessarily confusing if we change the naming style compared to the spec. Note, that the "non-compliant names" are localised to the VirtIO namespace.

However vaguely remember having the same discussion in #19757 and I ended up updating to PascalCase. So did the same here.

[ADKaster]

Glad to see more work on VirtIO devices! Hopefully using these guys makes it more pleasant to work with QEMU on non-x86 systems soon ™️