quoted

Any reason to use __packed and alignement here?
This structure will be copied in a vring buffer right?

Using __packed together with an explicit alignment is a common pattern for defining 
communication packets. The goal is to ensure a stable and predictable layout across 
different architectures and compilers.

Being mostly a netdev person, i can say that the network Maintainers
actually refuses patches with __packed. If you have designed your
protocol correctly, defined your structure correctly, you should not
need them.

We do however accept things like

	BUILD_BUG_ON(sizeof(strcut foo) != 8);

just to make sure the compile is doing what you expect.

	Andrew