libbpf: Support shared umems between queues and devices

Add support for shared umems between hardware queues and devices to
the AF_XDP part of libbpf. This so that zero-copy can be achieved in
applications that want to send and receive packets between HW queues
on one device or between different devices/netdevs.

In order to create sockets that share a umem between hardware queues
and devices, a new function has been added called
xsk_socket__create_shared(). It takes the same arguments as
xsk_socket_create() plus references to a fill ring and a completion
ring. So for every socket that share a umem, you need to have one more
set of fill and completion rings. This in order to maintain the
single-producer single-consumer semantics of the rings.

You can create all the sockets via the new xsk_socket__create_shared()
call, or create the first one with xsk_socket__create() and the rest
with xsk_socket__create_shared(). Both methods work.

Signed-off-by: Magnus Karlsson <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Björn Töpel <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: magnus-karlsson

tools/lib/bpf/libbpf.map

@@ -306,4 +306,5 @@ LIBBPF_0.2.0 {
 		perf_buffer__buffer_fd;
 		perf_buffer__epoll_fd;
 		perf_buffer__consume_buffer;
+		xsk_socket__create_shared;
 } LIBBPF_0.1.0;