zebra, lib: add an internal API to get relative default nsid in other ns

as remind, the netns identifiers are local to a namespace. that is to
say that for instance, a vrf <vrfx> will have a netns id value in one
netns, and have an other netns id value in one other netns.
There is a need for zebra daemon to collect some cross information, like
the LINK_NETNSID information from interfaces having link layer in an
other network namespace. For that, it is needed to have a global
overview instead of a relative overview per namespace.
The first brick of this change is an API that sticks to netlink API,
that uses NETNSA_TARGET_NSID. from a given vrf vrfX, and a new vrf
created vrfY, the API returns the value of nsID from vrfX, inside the
new vrf vrfY.
The brick also gets the ns id value of default namespace in each other
namespace. An additional value in ns.h is offered, that permits to
retrieve the default namespace context.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

include/linux/net_namespace.h

@@ -16,6 +16,7 @@ enum {
 	NETNSA_NSID,
 	NETNSA_PID,
 	NETNSA_FD,
+	NETNSA_TARGET_NSID,
 	__NETNSA_MAX,
 };
 

lib/netns_linux.c

@@ -590,3 +590,9 @@ ns_id_t ns_get_default_id(void)
 		return default_ns->ns_id;
 	return NS_DEFAULT_INTERNAL;
 }
+
+struct ns *ns_get_default(void)
+{
+	return default_ns;
+}
+

lib/ns.h

@@ -177,6 +177,7 @@ extern struct ns *ns_lookup_name(const char *name);
 extern int ns_enable(struct ns *ns, void (*func)(ns_id_t, void *));
 extern struct ns *ns_get_created(struct ns *ns, char *name, ns_id_t ns_id);
 extern void ns_disable(struct ns *ns);
+extern struct ns *ns_get_default(void);
 
 #ifdef __cplusplus
 }

zebra/zebra_netns_id.c

@@ -314,11 +314,101 @@ ns_id_t zebra_ns_id_get(const char *netnspath)
 	return return_nsid;
 }
 
+/* if nsid is not default one, get relative default ns for the new ns
+ * for instance, if default ns is 0 and a new ns "vrf1" id is 1,
+ * in  ns "vrf1", the default ns is not known. using GETNSID with
+ * two parameters: NETNS_NSID, and NETNS_TARGET_NSID will help
+ * in identifying that value
+ */
+ns_id_t zebra_ns_id_get_relative_value(ns_id_t ns_read, ns_id_t target_nsid)
+{
+	struct sockaddr_nl snl;
+	int sock, ret;
+	unsigned int seq;
+	ns_id_t return_nsid = NS_UNKNOWN;
+	char buf[NETLINK_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh;
+	struct rtgenmsg *rt;
+	int len;
+
+	if (ns_read == NS_UNKNOWN || target_nsid == NS_UNKNOWN)
+		return return_nsid;
+
+	/* netlink socket */
+	sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+	if (sock < 0) {
+		flog_err_sys(EC_LIB_SOCKET, "netlink( %u) socket() error: %s",
+			     sock, safe_strerror(errno));
+		return NS_UNKNOWN;
+	}
+	memset(&snl, 0, sizeof(snl));
+	snl.nl_family = AF_NETLINK;
+	snl.nl_groups = RTNLGRP_NSID;
+	snl.nl_pid = 0; /* AUTO PID */
+	ret = bind(sock, (struct sockaddr *)&snl, sizeof(snl));
+	if (ret < 0) {
+		flog_err_sys(EC_LIB_SOCKET,
+			     "netlink( %u) socket() bind error: %s", sock,
+			     safe_strerror(errno));
+		close(sock);
+		return NS_UNKNOWN;
+	}
+
+	/* message to send to netlink : GETNSID */
+	memset(buf, 0, NETLINK_SOCKET_BUFFER_SIZE);
+	nlh = initiate_nlh(buf, &seq, RTM_GETNSID);
+	rt = (struct rtgenmsg *)(buf + nlh->nlmsg_len);
+	nlh->nlmsg_len += NETLINK_ALIGN(sizeof(struct rtgenmsg));
+	rt->rtgen_family = AF_UNSPEC;
+
+	addattr32(nlh, NETLINK_SOCKET_BUFFER_SIZE, NETNSA_NSID, ns_read);
+	addattr32(nlh, NETLINK_SOCKET_BUFFER_SIZE, NETNSA_TARGET_NSID, target_nsid);
+
+	ret = send_receive(sock, nlh, seq, buf);
+	if (ret < 0) {
+		close(sock);
+		return NS_UNKNOWN;
+	}
+	nlh = (struct nlmsghdr *)buf;
+	len = ret;
+	ret = 0;
+	do {
+		if (nlh->nlmsg_type >= NLMSG_MIN_TYPE) {
+			return_nsid = extract_nsid(nlh, buf);
+			if (return_nsid != NS_UNKNOWN)
+				break;
+		} else if (nlh->nlmsg_type == NLMSG_ERROR) {
+			struct nlmsgerr *err =
+				(struct nlmsgerr
+				 *)((char *)nlh
+				    + NETLINK_ALIGN(sizeof(
+							   struct
+							   nlmsghdr)));
+			if (err->error < 0)
+				errno = -err->error;
+			else
+				errno = err->error;
+			break;
+		}
+		len = len - NETLINK_ALIGN(nlh->nlmsg_len);
+		nlh = (struct nlmsghdr *)((char *)nlh
+					  + NETLINK_ALIGN(
+							  nlh->nlmsg_len));
+	} while (len != 0 && ret == 0);
+
+	return return_nsid;
+}
+
 #else
 ns_id_t zebra_ns_id_get(const char *netnspath)
 {
 	return zebra_ns_id_get_fallback(netnspath);
 }
+
+ns_id_t zebra_ns_id_get_relative_value(ns_id_t ns_read, ns_id_t target_nsid)
+{
+	return NS_UNKNOWN;
+}
 #endif /* ! defined(HAVE_NETLINK) */
 
 #ifdef HAVE_NETNS

zebra/zebra_netns_id.h

@@ -26,6 +26,8 @@ extern "C" {
 
 extern ns_id_t zebra_ns_id_get(const char *netnspath);
 extern ns_id_t zebra_ns_id_get_default(void);
+extern ns_id_t zebra_ns_id_get_relative_value(ns_id_t ns_read,
+					      ns_id_t target_nsid);
 
 #ifdef __cplusplus
 }

zebra/zebra_netns_notify.c

@@ -72,7 +72,8 @@ static void zebra_ns_notify_create_context_from_entry_name(const char *name)
 	char *netnspath = ns_netns_pathname(NULL, name);
 	struct vrf *vrf;
 	int ret;
-	ns_id_t ns_id, ns_id_external;
+	ns_id_t ns_id, ns_id_external, ns_id_relative = NS_UNKNOWN;
+	struct ns *default_ns;
 
 	if (netnspath == NULL)
 		return;
@@ -82,6 +83,15 @@ static void zebra_ns_notify_create_context_from_entry_name(const char *name)
 	}
 	if (ns_id == NS_UNKNOWN)
 		return;
+	default_ns = ns_get_default();
+	if (default_ns && default_ns->internal_ns_id != ns_id) {
+		frr_with_privs(&zserv_privs) {
+			ns_id_relative =
+				zebra_ns_id_get_relative_value(
+							default_ns->internal_ns_id,
+							ns_id);
+		}
+	}
 	ns_id_external = ns_map_nsid_with_external(ns_id, true);
 	/* if VRF with NS ID already present */
 	vrf = vrf_lookup_by_id((vrf_id_t)ns_id_external);