iproute2: add libgenl files

Create libgenl.h and libgenl.c. They will contain
common code for GENL users such as ipl2tp, tcp_metrics, etc.

Somewhat simplified by Stephen Hemminger
Signed-off-by: Julian Anastasov <ja@ssi.bg>

include/libgenl.h

+#ifndef __LIBGENL_H__
+#define __LIBGENL_H__
+
+#include "libnetlink.h"
+
+#define GENL_REQUEST(_req, _hdrsiz, _bufsiz)				\
+struct {								\
+	struct nlmsghdr		n;					\
+	struct genlmsghdr	g;					\
+	char			buf[NLMSG_ALIGN(_hdrsiz) + (_bufsiz)];	\
+} _req
+
+#define GENL_INITIALIZER(_family, _hdrsiz, _ver, _cmd, _flags)		\
+	{								\
+		.n = {							\
+			.nlmsg_type = (_family),			\
+			.nlmsg_flags = (_flags),			\
+			.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN + (_hdrsiz)), \
+		},							\
+		.g = {							\
+			.cmd = (_cmd),					\
+			.version = (_ver),				\
+		},							\
+	}
+
+extern int genl_resolve_family(struct rtnl_handle *grth, const char *family);
+
+#endif /* __LIBGENL_H__ */

lib/Makefile

@@ -2,7 +2,7 @@ CFLAGS += -fPIC
 
 UTILOBJ=utils.o rt_names.o ll_types.o ll_proto.o ll_addr.o inet_proto.o
 
-NLOBJ=ll_map.o libnetlink.o
+NLOBJ=libgenl.o ll_map.o libnetlink.o
 
 all: libnetlink.a libutil.a
 

lib/libgenl.c

+/*
+ * libgenl.c	GENL library
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/genetlink.h>
+#include "libgenl.h"
+
+static int genl_parse_getfamily(struct nlmsghdr *nlh)
+{
+	struct rtattr *tb[CTRL_ATTR_MAX + 1];
+	struct genlmsghdr *ghdr = NLMSG_DATA(nlh);
+	int len = nlh->nlmsg_len;
+	struct rtattr *attrs;
+
+	if (nlh->nlmsg_type != GENL_ID_CTRL) {
+		fprintf(stderr, "Not a controller message, nlmsg_len=%d "
+			"nlmsg_type=0x%x\n", nlh->nlmsg_len, nlh->nlmsg_type);
+		return -1;
+	}
+
+	len -= NLMSG_LENGTH(GENL_HDRLEN);
+
+	if (len < 0) {
+		fprintf(stderr, "wrong controller message len %d\n", len);
+		return -1;
+	}
+
+	if (ghdr->cmd != CTRL_CMD_NEWFAMILY) {
+		fprintf(stderr, "Unknown controller command %d\n", ghdr->cmd);
+		return -1;
+	}
+
+	attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN);
+	parse_rtattr(tb, CTRL_ATTR_MAX, attrs, len);
+
+	if (tb[CTRL_ATTR_FAMILY_ID] == NULL) {
+		fprintf(stderr, "Missing family id TLV\n");
+		return -1;
+	}
+
+	return rta_getattr_u16(tb[CTRL_ATTR_FAMILY_ID]);
+}
+
+int genl_resolve_family(struct rtnl_handle *grth, const char *family)
+{
+	GENL_REQUEST(req, 0, 1024)
+		= GENL_INITIALIZER(GENL_ID_CTRL, 0,
+				   0, CTRL_CMD_GETFAMILY, NLM_F_REQUEST);
+
+	addattr_l(&req.n, 1024, CTRL_ATTR_FAMILY_NAME,
+		  family, strlen(family) + 1);
+
+	if (rtnl_talk(grth, &req.n, 0, 0, &req.n) < 0) {
+		fprintf(stderr, "Error talking to the kernel\n");
+		return -2;
+	}
+
+	return genl_parse_getfamily(&req.n);
+}
+