Initial commit

An example on generic netlink communications between the kernel
and user-space processes.

Makefile

@@ -0,0 +1,28 @@
+
+PKG_CONFIG=$(shell dirname ${CROSS_COMPILE})/pkg-config
+NL_LIBNAME=libnl-genl-3.0
+
+NL_LIB_FLAGS=$(shell $(PKG_CONFIG) --cflags $(NL_LIBNAME))
+NL_LIBS_L=$(shell $(PKG_CONFIG) --libs-only-L $(NL_LIBNAME))
+NL_LIBS_l=$(shell $(PKG_CONFIG) --libs-only-l $(NL_LIBNAME))
+
+CC=${CROSS_COMPILE}gcc
+
+.PHONY:all
+all: genl_ex genl_ex.ko
+
+genl_ex: genl_ex.h genl_ex.c
+	$(CC) -Wextra -Wall -Werror -Wno-unused-parameter $(NL_LIB_FLAGS) $(NL_LIBS_L) $(NL_LIBS_l) genl_ex.c -o genl_ex
+
+genl_ex.ko:
+	$(MAKE) -C $(shell pwd)/kernel KERNEL_DIR=$(KERNEL_DIR) 
+
+.PHONY: install
+install:
+	$(MAKE) -C $(shell pwd)/kernel install
+
+.PHONY: clean
+clean:
+	rm -f *.o genl_ex
+	$(MAKE) -C $(shell pwd)/kernel KERNEL_DIR=$(KERNEL_DIR) clean
+

genl_ex.c

@@ -0,0 +1,239 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <netlink/msg.h>
+#include <netlink/attr.h>
+
+#include "genl_ex.h"
+
+static char message[GENL_TEST_ATTR_MSG_MAX];
+static int send_to_kernel;
+static unsigned int mcgroups;		/* Mask of groups */
+
+static void usage(char* name)
+{
+	printf("Usage: %s\n"
+		"	-h : this help message\n"
+		"	-l : listen on one or more groups, comma separated\n"
+		"	-m : the message to send, required with -s\n"
+		"	-s : send to kernel\n"
+		"NOTE: specify either l or s, not both\n",
+		name);
+}
+
+static void add_group(char* group)
+{
+	unsigned int grp = strtoul(group, NULL, 10);
+
+	if (grp > GENL_TEST_MCGRP_MAX-1) {
+		fprintf(stderr, "Invalid group number %u. Values allowed 0:%u\n",
+			grp, GENL_TEST_MCGRP_MAX-1);
+		exit(EXIT_FAILURE);
+	}
+
+	mcgroups |= 1 << (grp);
+}
+
+static void parse_cmd_line(int argc, char** argv)
+{
+	char* opt_val;
+
+	while (1) {
+		int opt = getopt(argc, argv, "hl:m:s");
+
+		if (opt == EOF)
+			break;
+
+		switch (opt) {
+		case 'h':
+			usage(argv[0]);
+			exit(EXIT_SUCCESS);
+
+		case 'l':
+			opt_val = strtok(optarg, ",");
+			add_group(opt_val); 
+			while ((opt_val = strtok(NULL, ",")))
+				add_group(opt_val); 
+
+			break;
+
+		case 'm':
+			strncpy(message, optarg, GENL_TEST_ATTR_MSG_MAX);
+			message[GENL_TEST_ATTR_MSG_MAX - 1] = '\0';
+			break;
+
+		case 's':
+			send_to_kernel = 1;
+			break;
+
+		default:
+			fprintf(stderr, "Unkown option %c !!\n", opt);
+			exit(EXIT_FAILURE);
+		}
+
+	}
+
+	/* sanity checks */
+	if (send_to_kernel && mcgroups)  {
+		fprintf(stderr, "I can either receive or send messages.\n\n");
+		usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}	
+	if (!send_to_kernel && !mcgroups)  {
+		fprintf(stderr, "Nothing to do!\n");
+		usage(argv[0]);
+		exit(EXIT_SUCCESS);
+	}
+	if (send_to_kernel && message[0]=='\0') {
+		fprintf(stderr, "What is the message you want to send?\n");
+		usage(argv[0]);
+		exit(EXIT_FAILURE);
+	}
+}
+static int send_msg_to_kernel(struct nl_sock *sock)
+{
+	struct nl_msg* msg;
+	int family_id, err = 0;
+
+	family_id = genl_ctrl_resolve(sock, GENL_TEST_FAMILY_NAME);
+	if(family_id < 0){
+		fprintf(stderr, "Unable to resolve family name!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	msg = nlmsg_alloc();
+	if (!msg) {
+		fprintf(stderr, "failed to allocate netlink message\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if(!genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, family_id, 0, 
+		NLM_F_REQUEST, GENL_TEST_C_MSG, 0)) {
+		fprintf(stderr, "failed to put nl hdr!\n");
+		err = -ENOMEM;
+		goto out;
+	}
+
+	err = nla_put_string(msg, GENL_TEST_ATTR_MSG, message);
+	if (err) {
+		fprintf(stderr, "failed to put nl string!\n");
+		goto out;
+	}
+
+	err = nl_send_auto(sock, msg);
+	if (err < 0) {
+		fprintf(stderr, "failed to send nl message!\n");
+	}
+
+out:
+	nlmsg_free(msg);
+	return err;
+}
+
+static int skip_seq_check(struct nl_msg *msg, void *arg)
+{
+	return NL_OK;
+}
+
+static int print_rx_msg(struct nl_msg *msg, void* arg)
+{
+	struct nlattr *attr[GENL_TEST_ATTR_MAX+1];
+
+	genlmsg_parse(nlmsg_hdr(msg), 0, attr, 
+			GENL_TEST_ATTR_MAX, genl_test_policy);
+
+	if (!attr[GENL_TEST_ATTR_MSG]) {
+		fprintf(stdout, "Kernel sent empty message!!\n");
+		return NL_OK;
+	}
+
+	fprintf(stdout, "Kernel says: %s \n", 
+		nla_get_string(attr[GENL_TEST_ATTR_MSG]));
+
+	return NL_OK;
+}
+
+static void prep_nl_sock(struct nl_sock** nlsock)
+{
+	int family_id, grp_id;
+	unsigned int bit = 0;
+
+	*nlsock = nl_socket_alloc();
+	if(!*nlsock) {
+		fprintf(stderr, "Unable to alloc nl socket!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* disable seq checks on multicast sockets */
+	nl_socket_disable_seq_check(*nlsock);
+	nl_socket_disable_auto_ack(*nlsock);
+
+	/* connect to genl */
+	if (genl_connect(*nlsock)) {
+		fprintf(stderr, "Unable to connect to genl!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	/* resolve the generic nl family id*/
+	family_id = genl_ctrl_resolve(*nlsock, GENL_TEST_FAMILY_NAME);
+	if(family_id < 0){
+		fprintf(stderr, "Unable to resolve family name!\n");
+		exit(EXIT_FAILURE);
+	}
+
+	if (!mcgroups)
+		return;
+
+	while (bit < sizeof(unsigned int)) {
+		if (!(mcgroups & (1 << bit)))
+			goto next;
+
+		grp_id = genl_ctrl_resolve_grp(*nlsock, GENL_TEST_FAMILY_NAME,
+				genl_test_mcgrp_names[bit]);
+
+		if (grp_id < 0)	{
+			fprintf(stderr, "Unable to resolve group name for %u!\n",
+				(1 << bit));
+			exit(EXIT_FAILURE);
+		}
+		if (nl_socket_add_membership(*nlsock, grp_id)) {
+			fprintf(stderr, "Unable to join group %u!\n", 
+				(1 << bit));
+			exit(EXIT_FAILURE);
+		}
+next:
+		bit++;
+	}
+}
+
+int main(int argc, char** argv)
+{
+	struct nl_sock* nlsock = NULL;
+	struct nl_cb *cb = NULL;
+	int ret;
+
+	parse_cmd_line(argc, argv);
+
+	prep_nl_sock(&nlsock);
+
+	if (send_to_kernel) {
+		ret = send_msg_to_kernel(nlsock);
+		exit(EXIT_SUCCESS);
+	}
+
+	/* prep the cb */
+	cb = nl_cb_alloc(NL_CB_DEFAULT);
+	nl_cb_set(cb, NL_CB_SEQ_CHECK, NL_CB_CUSTOM, skip_seq_check, NULL);
+	nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, print_rx_msg, NULL);
+	do {
+		ret = nl_recvmsgs(nlsock, cb);
+	} while (!ret);
+
+	nl_cb_put(cb);
+	return 0;
+}

genl_ex.h

@@ -0,0 +1,59 @@
+
+#ifndef GENL_TEST_H
+#define GENL_TEST_H
+
+#include <linux/netlink.h>
+
+#ifndef __KERNEL__
+#include <netlink/genl/genl.h>
+#include <netlink/genl/family.h>
+#include <netlink/genl/ctrl.h>
+#endif
+
+#define GENL_TEST_FAMILY_NAME		"genl_test"
+#define GENL_TEST_MCGRP0_NAME		"genl_mcgrp0"
+#define GENL_TEST_MCGRP1_NAME		"genl_mcgrp1"
+#define GENL_TEST_MCGRP2_NAME		"genl_mcgrp2"
+
+#define GENL_TEST_ATTR_MSG_MAX		256
+#define GENL_TEST_HELLO_INTERVAL	5000
+
+enum {
+	GENL_TEST_C_UNSPEC,		/* Must NOT use element 0 */
+	GENL_TEST_C_MSG,
+};
+
+enum genl_test_multicast_groups {
+	GENL_TEST_MCGRP0,
+	GENL_TEST_MCGRP1,
+	GENL_TEST_MCGRP2,
+};
+#define GENL_TEST_MCGRP_MAX		3
+
+static char* genl_test_mcgrp_names[GENL_TEST_MCGRP_MAX] = {
+	GENL_TEST_MCGRP0_NAME,
+	GENL_TEST_MCGRP1_NAME,
+	GENL_TEST_MCGRP2_NAME,
+};
+
+enum genl_test_attrs {
+	GENL_TEST_ATTR_UNSPEC,		/* Must NOT use element 0 */
+
+	GENL_TEST_ATTR_MSG,
+
+	__GENL_TEST_ATTR__MAX,
+};
+#define GENL_TEST_ATTR_MAX (__GENL_TEST_ATTR__MAX - 1)
+
+static struct nla_policy genl_test_policy[GENL_TEST_ATTR_MAX+1] = {
+	[GENL_TEST_ATTR_MSG] = {
+		.type = NLA_STRING,
+#ifdef __KERNEL__
+		.len = GENL_TEST_ATTR_MSG_MAX
+#else
+		.maxlen = GENL_TEST_ATTR_MSG_MAX
+#endif
+	},
+};
+
+#endif