[messe]

> While it's true that writers need to be aware of buffering to make use of fancy syscalls, implementing that should be an option, but not a requirement.

Buffering is implemented and handled in the vtable struct itself, the writers (implentations of the interface) themselves don't actually have to know or care about it other than passing through the user-provided buffer when initializing the vtable.

If you don't want buffering, you can pass a zero-length buffer upon creation, and it'll get optimized out. This optimization doesn't require devirtualization because the buffering happens before any virtual function calls.