To avoid the copy data is passed to and from the application in special buffers
described by a struct onload_zc_iovec. A message or datagram
can consist of multiple iovecs using a struct onload_zc_msg. A
single call to send can involve multiple messages using an array of struct onload_zc_mmsg.
Figure 1. Zero-Copy Data Buffers
/* A zc_iovec describes a single buffer */
struct onload_zc_iovec {
void* iov_base; /* Address within buffer */
size_t iov_len; /* Length of data */
onload_zc_handle buf; /* (opaque) buffer handle */
unsigned iov_flags; /* Not currently used */
};
/* A msg describes array of iovecs that make up datagram */
struct onload_zc_msg {
struct onload_zc_iovec* iov; /* Array of buffers */
struct msghdr msghdr; /* Message metadata */
};
/* An mmsg describes a message, the socket, and its result */
struct onload_zc_mmsg {
struct onload_zc_msg msg; /* Message */
int rc; /* Result of send operation */
int fd; /* socket to send on */
};