Initial handshake: allow exchanging RDMA parameters

Before starting a RDMA communication between two nodes, local
informations must be exchanged. The proposed example uses UDP
for that purpose.

Makefile

+HEADERS = udp.h
+CFLAGS = -Wall -O3
+
+udp_send: udp_send.c
+	gcc $(CFLAGS) -o $@ $?
+
+udp_recv: udp_recv.c
+	gcc $(CFLAGS) -o $@ $?
+
+all: udp_send udp_recv
+

README.md

+# RDMA minimal working example
+
+Minimal working example for RDMA with multiple slaves: one machine serves a portion of memory and the others can read it.
+

udp_rdma.h

+struct udp_query_parameters {
+	uint8_t requested;
+};
+
+#define REQ_LID 0x1
+#define REQ_QPN 0x2
+#define REQ_ADDR 0x4
+#define REQ_SIZE 0x8
+#define REQ_KEY 0x10
+
+struct udp_rdma_parameters {
+	uint16_t lid;
+	uint32_t qpn;
+	void *addr;
+	size_t size;
+	uint32_t key;
+};
+

udp_recv.c

+#include <netdb.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include "udp_rdma.h"
+
+int main(void) {
+	struct addrinfo server_hints;
+	struct addrinfo *server_infos;
+	struct sockaddr client_addr;
+
+	struct udp_query_parameters *rdma_req_params;
+	struct udp_rdma_parameters rdma_params;
+
+	socklen_t client_addr_size = sizeof(struct sockaddr_storage);
+	const size_t buffer_length = sizeof(struct udp_query_parameters);
+	int result, server_socket;
+	char receive_buffer[buffer_length];
+
+	// Set up bind address
+	memset(&server_hints, 0, sizeof(struct addrinfo));
+	server_hints.ai_family = AF_INET;
+	server_hints.ai_socktype = SOCK_DGRAM;
+	server_hints.ai_flags = AI_PASSIVE;
+
+	result = getaddrinfo(NULL, "7362", &server_hints, &server_infos);
+	if(result != 0) {
+		fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(result));
+		return 1;
+	}
+
+	// Create a socket an bind
+	// XXX: assumes first address in linked list is 0.0.0.0
+	server_socket = socket(server_infos->ai_family, server_infos->ai_socktype, server_infos->ai_protocol);
+	if(server_socket == -1) {
+		perror("socket error");
+		return 1;
+	}
+
+	result = bind(server_socket, server_infos->ai_addr, server_infos->ai_addrlen);
+	if(result == -1) {
+		perror("bind error");
+		return 1;
+	}
+
+	// Address info can be freed as soon as the socket in bound
+	freeaddrinfo(server_infos);
+
+	result = recvfrom(server_socket, receive_buffer, buffer_length, 0, &client_addr, &client_addr_size);
+	if(result == -1) {
+		perror("recvfrom error");
+		return 1;
+	}
+
+	rdma_req_params = (struct udp_query_parameters *) receive_buffer;
+	printf("Client requested: %d", rdma_req_params->requested);
+
+	// XXX: stop using dummy data and take account of capabilities
+	rdma_params.lid = 0x1234;
+	rdma_params.qpn = 0x12345678;
+	rdma_params.addr = (void *) receive_buffer;
+	rdma_params.size = buffer_length;
+	rdma_params.key = 0x87654321;
+
+	result = sendto(server_socket, (void *) &rdma_params, sizeof(struct udp_rdma_parameters), MSG_CONFIRM, &client_addr, client_addr_size);
+	if(result == -1) {
+		perror("sendto error");
+		return 1;
+	}
+
+	close(server_socket);
+
+	return 0;
+}
+

udp_send.c

+#include <netdb.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+#include "udp_rdma.h"
+
+int main(void) {
+	struct addrinfo server_hints;
+	struct addrinfo *server_infos;
+
+	struct udp_query_parameters rdma_req_params;
+	struct udp_rdma_parameters *rdma_params;
+
+	const size_t buffer_length = sizeof(struct udp_rdma_parameters);
+	int result, server_socket;
+	char receive_buffer[buffer_length];
+
+	// Set up remote address
+	memset(&server_hints, 0, sizeof(struct addrinfo));
+	server_hints.ai_family = AF_INET;
+	server_hints.ai_socktype = SOCK_DGRAM;
+
+	result = getaddrinfo("192.168.16.10", "7362", &server_hints, &server_infos);
+	if(result != 0) {
+		fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(result));
+		return 1;
+	}
+
+	// Create a socket
+	// XXX: assumes first address in linked list is 0.0.0.0
+	server_socket = socket(server_infos->ai_family, server_infos->ai_socktype, server_infos->ai_protocol);
+	if(server_socket == -1) {
+		perror("socket error");
+		return 1;
+	}
+
+	// Create and send a query with full capabilities
+	rdma_req_params.requested = REQ_LID | REQ_QPN | REQ_ADDR | REQ_SIZE | REQ_KEY;
+	result = sendto(server_socket, (void *) &rdma_req_params, sizeof(struct udp_query_parameters), 0, server_infos->ai_addr, server_infos->ai_addrlen);
+	if(result == -1) {
+		perror("sendto error");
+		return 1;
+	}
+
+	// Wait for informations from the server
+	result = recvfrom(server_socket, receive_buffer, buffer_length, 0, server_infos->ai_addr, &server_infos->ai_addrlen);
+	if(result == -1) {
+		perror("recvfrom error");
+		return 1;
+	}
+
+	rdma_params = (struct udp_rdma_parameters *) receive_buffer;
+	printf("Client LID: %d", rdma_params->lid);
+
+	close(server_socket);
+	freeaddrinfo(server_infos);
+
+	return 0;
+}
+