copyin+copyout in one step ?

[Zaphod Beeblebrox]

On Mon, May 27, 2013 at 7:38 PM, Luigi Rizzo <rizzo at iet.unipi.it> wrote:

>
> say a process P1 wants to use the kernel to copy the content of a
> buffer SRC (in its user address space) to a buffer DST (in the
> address space of another process P2), and assume that P1 issues the
> request to the kernel when P2 has already told the kernel where the
> data should go:
>

Urm... Isn't the use of shared memory the more obvious way to transfer data
between processes?  Am I missing some nuance?