[Samba] samba can sendfile, but why no receivefile?

[jason]

Hi all:

Samba can use sendfile to improve the performance of READ, but it does not
have receivefile to improve the performance of WRITE. What is the reason?

I just find linux kernel function:
int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
    sk_read_actor_t recv_actor)

which suppose is the conterpart of sendfile(). But it seems almost nobody
use it to do something.

Jason