1 files changed, 159 insertions, 0 deletions
diff --git a/lib/libgenl.c b/lib/libgenl.c
new file mode 100644
index 0000000..fca07f9
--- /dev/null
+++ b/lib/libgenl.c
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * libgenl.c	GENL library
+ */
+
+#include <errno.h>
+#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, 1024, GENL_ID_CTRL, 0, 0, CTRL_CMD_GETFAMILY,
+		     NLM_F_REQUEST);
+	struct nlmsghdr *answer;
+	int fnum;
+
+	addattr_l(&req.n, sizeof(req), CTRL_ATTR_FAMILY_NAME,
+		  family, strlen(family) + 1);
+
+	if (rtnl_talk(grth, &req.n, &answer) < 0) {
+		fprintf(stderr, "Error talking to the kernel\n");
+		return -2;
+	}
+
+	fnum = genl_parse_getfamily(answer);
+	free(answer);
+
+	return fnum;
+}
+
+static int genl_parse_grps(struct rtattr *attr, const char *name, unsigned int *id)
+{
+	const struct rtattr *pos;
+
+	rtattr_for_each_nested(pos, attr) {
+		struct rtattr *tb[CTRL_ATTR_MCAST_GRP_MAX + 1];
+
+		parse_rtattr_nested(tb, CTRL_ATTR_MCAST_GRP_MAX, pos);
+
+		if (tb[CTRL_ATTR_MCAST_GRP_NAME] && tb[CTRL_ATTR_MCAST_GRP_ID]) {
+			if (strcmp(name, rta_getattr_str(tb[CTRL_ATTR_MCAST_GRP_NAME])) == 0) {
+				*id = rta_getattr_u32(tb[CTRL_ATTR_MCAST_GRP_ID]);
+				return 0;
+			}
+		}
+	}
+
+	errno = ENOENT;
+	return -1;
+}
+
+int genl_add_mcast_grp(struct rtnl_handle *grth, __u16 fnum, const char *group)
+{
+	GENL_REQUEST(req, 1024, GENL_ID_CTRL, 0, 0, CTRL_CMD_GETFAMILY,
+		     NLM_F_REQUEST);
+	struct rtattr *tb[CTRL_ATTR_MAX + 1];
+	struct nlmsghdr *answer = NULL;
+	struct genlmsghdr *ghdr;
+	struct rtattr *attrs;
+	int len, ret = -1;
+	unsigned int id;
+
+	addattr16(&req.n, sizeof(req), CTRL_ATTR_FAMILY_ID, fnum);
+
+	if (rtnl_talk(grth, &req.n, &answer) < 0) {
+		fprintf(stderr, "Error talking to the kernel\n");
+		return -2;
+	}
+
+	ghdr = NLMSG_DATA(answer);
+	len = answer->nlmsg_len;
+
+	if (answer->nlmsg_type != GENL_ID_CTRL) {
+		errno = EINVAL;
+		goto err_free;
+	}
+
+	len -= NLMSG_LENGTH(GENL_HDRLEN);
+	if (len < 0) {
+		errno = EINVAL;
+		goto err_free;
+	}
+
+	attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN);
+	parse_rtattr(tb, CTRL_ATTR_MAX, attrs, len);
+
+	if (tb[CTRL_ATTR_MCAST_GROUPS] == NULL) {
+		errno = ENOENT;
+		fprintf(stderr, "Missing mcast groups TLV\n");
+		goto err_free;
+	}
+
+	if (genl_parse_grps(tb[CTRL_ATTR_MCAST_GROUPS], group, &id) < 0)
+		goto err_free;
+
+	ret = rtnl_add_nl_group(grth, id);
+
+err_free:
+	free(answer);
+	return ret;
+}
+
+int genl_init_handle(struct rtnl_handle *grth, const char *family,
+		     int *genl_family)
+{
+	if (*genl_family >= 0)
+		return 0;
+
+	if (rtnl_open_byproto(grth, 0, NETLINK_GENERIC) < 0) {
+		fprintf(stderr, "Cannot open generic netlink socket\n");
+		return -1;
+	}
+
+	*genl_family = genl_resolve_family(grth, family);
+	if (*genl_family < 0)
+		return -1;
+
+	return 0;
+}