Generic Netlink multicast groups support

I have a patch against commit d378220c96
extending libnl with a facility to receive generic netlink messages sent
to multicast groups.

Essentially it add one new function genl_ctrl_resolve_grp which
prototype looks like this
int genl_ctrl_resolve_grp(struct nl_sock *sk, const char *family_name,
        const char *grp_name)
It resolves  the family name and the group name to group id. Then
the returned id can be used in nl_socket_add_membership to subscribe
to multicast messages.

Besides that it adds two more functions

uint32_t nl_socket_get_peer_groups(struct nl_sock *sk)
void nl_socket_set_peer_groups(struct nl_sock *sk, uint32_t groups)

allowing to modify the socket peer groups field. So it's possible to
multicast messages from the user space using the legacy interface.
Looks like there is no way (or I was not able to find one?) to modify
the netlink socket destination group from the user space, when the
group id is greater then 32.

include/linux/genetlink.h

@@ -1,6 +1,7 @@
 #ifndef __LINUX_GENERIC_NETLINK_H
 #define __LINUX_GENERIC_NETLINK_H
 
+#include <linux/types.h>
 #include <linux/netlink.h>
 
 #define GENL_NAMSIZ	16	/* length of family name */
@@ -39,6 +40,9 @@ enum {
 	CTRL_CMD_NEWOPS,
 	CTRL_CMD_DELOPS,
 	CTRL_CMD_GETOPS,
+	CTRL_CMD_NEWMCAST_GRP,
+	CTRL_CMD_DELMCAST_GRP,
+	CTRL_CMD_GETMCAST_GRP, /* unused */
 	__CTRL_CMD_MAX,
 };
 
@@ -52,6 +56,7 @@ enum {
 	CTRL_ATTR_HDRSIZE,
 	CTRL_ATTR_MAXATTR,
 	CTRL_ATTR_OPS,
+	CTRL_ATTR_MCAST_GROUPS,
 	__CTRL_ATTR_MAX,
 };
 
@@ -66,4 +71,13 @@ enum {
 
 #define CTRL_ATTR_OP_MAX (__CTRL_ATTR_OP_MAX - 1)
 
+enum {
+	CTRL_ATTR_MCAST_GRP_UNSPEC,
+	CTRL_ATTR_MCAST_GRP_NAME,
+	CTRL_ATTR_MCAST_GRP_ID,
+	__CTRL_ATTR_MCAST_GRP_MAX,
+};
+
+#define CTRL_ATTR_MCAST_GRP_MAX (__CTRL_ATTR_MCAST_GRP_MAX - 1)
+
 #endif	/* __LINUX_GENERIC_NETLINK_H */

include/netlink-types.h

@@ -702,6 +702,13 @@ struct genl_family_op
 	struct nl_list_head	o_list;
 };
 
+struct genl_family_grp {
+        struct genl_family      *family;        /* private */
+        struct nl_list_head     list;           /* private */
+        char                    name[GENL_NAMSIZ];
+        u_int32_t               id;
+};
+
 struct genl_family
 {
 	NLHDR_COMMON
@@ -713,6 +720,7 @@ struct genl_family
 	uint32_t		gf_maxattr;
 
 	struct nl_list_head	gf_ops;
+	struct nl_list_head	gf_mc_grps;
 };
 
 union nfnl_ct_proto

include/netlink/genl/ctrl.h

@@ -29,6 +29,9 @@ extern struct genl_family *	genl_ctrl_search_by_name(struct nl_cache *,
 							 const char *);
 extern int			genl_ctrl_resolve(struct nl_sock *,
 						  const char *);
+extern int 			genl_ctrl_resolve_grp(struct nl_sock *sk,
+						      const char *family,
+						      const char *grp);
 
 #ifdef __cplusplus
 }

include/netlink/genl/family.h

@@ -42,6 +42,9 @@ extern void			genl_family_set_maxattr(struct genl_family *,
 
 extern int			genl_family_add_op(struct genl_family *,
 						   int, int);
+extern int 			genl_family_add_grp(struct genl_family *,
+					uint32_t , const char *);
+
 
 #ifdef __cplusplus
 }

include/netlink/genl/genl.h

@@ -21,7 +21,6 @@ extern "C" {
 #endif
 
 extern int		genl_connect(struct nl_sock *);
-
 extern int		genl_send_simple(struct nl_sock *, int, int,
 					 int, int);
 

include/netlink/socket.h

@@ -37,7 +37,8 @@ extern void		nl_join_groups(struct nl_sock *, int);
 extern uint32_t		nl_socket_get_peer_port(struct nl_sock *);
 extern void		nl_socket_set_peer_port(struct nl_sock *,
 							uint32_t);
-
+extern uint32_t 	nl_socket_get_peer_groups(struct nl_sock *sk);
+extern void 		nl_socket_set_peer_groups(struct nl_sock *sk, uint32_t groups);
 extern struct nl_cb *	nl_socket_get_cb(struct nl_sock *);
 extern void		nl_socket_set_cb(struct nl_sock *,
 						 struct nl_cb *);

lib/genl/ctrl.c

@@ -45,6 +45,7 @@ static struct nla_policy ctrl_policy[CTRL_ATTR_MAX+1] = {
 	[CTRL_ATTR_HDRSIZE]	= { .type = NLA_U32 },
 	[CTRL_ATTR_MAXATTR]	= { .type = NLA_U32 },
 	[CTRL_ATTR_OPS]		= { .type = NLA_NESTED },
+	[CTRL_ATTR_MCAST_GROUPS] = { .type = NLA_NESTED },
 };
 
 static struct nla_policy family_op_policy[CTRL_ATTR_OP_MAX+1] = {
@@ -52,6 +53,11 @@ static struct nla_policy family_op_policy[CTRL_ATTR_OP_MAX+1] = {
 	[CTRL_ATTR_OP_FLAGS]	= { .type = NLA_U32 },
 };
 
+static struct nla_policy family_grp_policy[CTRL_ATTR_MCAST_GRP_MAX+1] = {
+	[CTRL_ATTR_MCAST_GRP_NAME] = { .type = NLA_STRING },
+	[CTRL_ATTR_MCAST_GRP_ID]   = { .type = NLA_U32 },
+};
+
 static int ctrl_msg_parser(struct nl_cache_ops *ops, struct genl_cmd *cmd,
 			   struct genl_info *info, void *arg)
 {
@@ -126,6 +132,40 @@ static int ctrl_msg_parser(struct nl_cache_ops *ops, struct genl_cmd *cmd,
 
 		}
 	}
+	
+	if (info->attrs[CTRL_ATTR_MCAST_GROUPS]) {
+		struct nlattr *nla, *nla_grps;
+		int remaining;
+
+		nla_grps = info->attrs[CTRL_ATTR_MCAST_GROUPS];
+		nla_for_each_nested(nla, nla_grps, remaining) {
+			struct nlattr *tb[CTRL_ATTR_MCAST_GRP_MAX+1];
+			int id;
+			const char * name;
+
+			err = nla_parse_nested(tb, CTRL_ATTR_MCAST_GRP_MAX, nla,
+					       family_grp_policy);
+			if (err < 0)
+				goto errout;
+
+			if (tb[CTRL_ATTR_MCAST_GRP_ID] == NULL) {
+				err = -NLE_MISSING_ATTR;
+				goto errout;
+			}
+			id = nla_get_u32(tb[CTRL_ATTR_MCAST_GRP_ID]);
+
+			if (tb[CTRL_ATTR_MCAST_GRP_NAME] == NULL) {
+				err = -NLE_MISSING_ATTR;
+				goto errout;
+			}
+			name = nla_get_string(tb[CTRL_ATTR_MCAST_GRP_NAME]);
+
+			err = genl_family_add_grp(family, id, name);
+			if (err < 0)
+				goto errout;
+		}
+
+	}
 
 	err = pp->pp_cb((struct nl_object *) family, pp);
 errout:
@@ -242,6 +282,44 @@ errout:
 	return err;
 }
 
+static int genl_ctrl_grp_by_name(const struct genl_family *family,
+				const char *grp_name)
+{
+	struct genl_family_grp *grp;
+
+	nl_list_for_each_entry(grp, &family->gf_mc_grps, list) {
+		if (!strcmp(grp->name, grp_name)) {
+			return grp->id;
+		}
+	}
+
+	return 0;
+}
+
+int genl_ctrl_resolve_grp(struct nl_sock *sk, const char *family_name,
+	const char *grp_name)
+{
+	struct nl_cache *cache;
+	struct genl_family *family;
+	int err;
+
+	if ((err = genl_ctrl_alloc_cache(sk, &cache)) < 0)
+		return err;
+
+	family = genl_ctrl_search_by_name(cache, family_name);
+	if (family == NULL) {
+		err = -NLE_OBJ_NOTFOUND;
+		goto errout;
+	}
+
+	err = genl_ctrl_grp_by_name(family, grp_name);
+	genl_family_put(family);
+errout:
+	nl_cache_free(cache);
+
+	return err;
+}
+
 /** @} */
 
 static struct genl_cmd genl_cmds[] = {

lib/genl/family.c

@@ -39,12 +39,14 @@ static void family_constructor(struct nl_object *c)
 	struct genl_family *family = (struct genl_family *) c;
 
 	nl_init_list_head(&family->gf_ops);
+	nl_init_list_head(&family->gf_mc_grps);
 }
 
 static void family_free_data(struct nl_object *c)
 {
 	struct genl_family *family = (struct genl_family *) c;
 	struct genl_family_op *ops, *tmp;
+	struct genl_family_grp *grp, *t_grp;
 
 	if (family == NULL)
 		return;
@@ -53,6 +55,12 @@ static void family_free_data(struct nl_object *c)
 		nl_list_del(&ops->o_list);
 		free(ops);
 	}
+
+	nl_list_for_each_entry_safe(grp, t_grp, &family->gf_mc_grps, list) {
+		nl_list_del(&grp->list);
+		free(grp);
+	}
+
 }
 
 static int family_clone(struct nl_object *_dst, struct nl_object *_src)
@@ -60,6 +68,7 @@ static int family_clone(struct nl_object *_dst, struct nl_object *_src)
 	struct genl_family *dst = nl_object_priv(_dst);
 	struct genl_family *src = nl_object_priv(_src);
 	struct genl_family_op *ops;
+	struct genl_family_grp *grp;
 	int err;
 
 	nl_list_for_each_entry(ops, &src->gf_ops, o_list) {
@@ -67,6 +76,13 @@ static int family_clone(struct nl_object *_dst, struct nl_object *_src)
 		if (err < 0)
 			return err;
 	}
+
+	nl_list_for_each_entry(grp, &src->gf_mc_grps, list) {
+		err = genl_family_add_grp(dst, grp->id, grp->name);
+		if (err < 0)
+			return err;
+	}
+
 	
 	return 0;
 }
@@ -93,6 +109,7 @@ static char *ops_flags2str(int flags, char *buf, size_t len)
 
 static void family_dump_details(struct nl_object *obj, struct nl_dump_params *p)
 {
+	struct genl_family_grp *grp;
 	struct genl_family *family = (struct genl_family *) obj;
 
 	family_dump_line(obj, p);
@@ -118,6 +135,11 @@ static void family_dump_details(struct nl_object *obj, struct nl_dump_params *p)
 			nl_dump(p, "\n");
 		}
 	}
+
+	nl_list_for_each_entry(grp, &family->gf_mc_grps, list) {
+		nl_dump_line(p, "      grp %s (0x%02x)\n", grp->name, grp->id);
+	}
+
 }
 
 static void family_dump_stats(struct nl_object *obj, struct nl_dump_params *p)
@@ -255,6 +277,23 @@ int genl_family_add_op(struct genl_family *family, int id, int flags)
 	return 0;
 }
 
+int genl_family_add_grp(struct genl_family *family, uint32_t id,
+	       		const char *name)
+{
+	struct genl_family_grp *grp;  
+
+	grp = calloc(1, sizeof(*grp));
+	if (grp == NULL)
+		return -NLE_NOMEM;
+
+	grp->id = id;
+	strncpy(grp->name, name, GENL_NAMSIZ - 1);
+
+	nl_list_add_tail(&grp->list, &family->gf_mc_grps);
+
+	return 0;
+}
+
 /** @} */
 
 /** @cond SKIP */

lib/nl.c

@@ -387,7 +387,7 @@ errout:
  * Receives a netlink message, allocates a buffer in \c *buf and
  * stores the message content. The peer's netlink address is stored
  * in \c *nla. The caller is responsible for freeing the buffer allocated
- * in \c *buf if a positive value is returned.  Interruped system calls
+ * in \c *buf if a positive value is returned.  Interrupted system calls
  * are handled by repeating the read. The input buffer size is determined
  * by peeking before the actual read is done.
  *

lib/socket.c

@@ -398,6 +398,18 @@ void nl_socket_set_peer_port(struct nl_sock *sk, uint32_t port)
 	sk->s_peer.nl_pid = port;
 }
 
+uint32_t nl_socket_get_peer_groups(struct nl_sock *sk)
+{
+	return sk->s_peer.nl_groups;
+}
+
+void nl_socket_set_peer_groups(struct nl_sock *sk, uint32_t groups)
+{
+	sk->s_peer.nl_groups = groups;
+}
+
+
+
 /** @} */
 
 /**