Kdbus meets linux-kernel

> So, it's the sender's decision whether to zero-copy, instead of the kernel's?

The sender needs to provide data in a way suitable for zero-copy. For kdbus, this means it has to be in a memfd. Whether the kernel passes this data around via the fd, or whether it inlines it into the receiver's buffer, is *not* controlled by the sender. So far, kdbus always passes data the same way it received it, though.