BUG/MEDIUM: namespace: close open namespaces during soft shutdown

When doing a soft shutdown, we won't be making new connections anymore so
there's no point in keeping the namespace file descriptors open anymore.

Keeping these open effectively makes it impossible to properly clean up
namespaces which are no longer used in the new configuration until all
previously opened connections are closed in the old worker process.

This change introduces a cleanup function that is called during soft shutdown
that closes all namespace file descriptors by iterating over the namespace
ebtree.

(cherry picked from commit 710d987cd62ab0779418f14aa2168dc10ef6bac7)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/namespace.c b/src/namespace.c
index 8a2e5a7..d1d8a47 100644
--- a/src/namespace.c
+++ b/src/namespace.c
@@ -15,6 +15,7 @@
 #include <common/hash.h>
 #include <common/errors.h>
 #include <proto/log.h>
+#include <proto/signal.h>
 #include <types/global.h>
 
 /* Opens the namespace <ns_name> and returns the FD or -1 in case of error
@@ -39,6 +40,24 @@
 
 static struct eb_root namespace_tree_root = EB_ROOT;
 
+static void netns_sig_stop(struct sig_handler *sh)
+{
+	struct ebpt_node *node, *next;
+	struct netns_entry *entry;
+
+	/* close namespace file descriptors and remove registered namespaces from the
+	 * tree when stopping */
+	node = ebpt_first(&namespace_tree_root);
+	while (node) {
+		next = ebpt_next(node);
+		ebpt_delete(node);
+		entry = container_of(node, struct netns_entry, node);
+		free(entry->node.key);
+		close(entry->fd);
+		node = next;
+	}
+}
+
 int netns_init(void)
 {
 	int err_code = 0;
@@ -55,6 +74,8 @@
 		}
 	}
 
+	signal_register_fct(0, netns_sig_stop, 0);
+
 	return err_code;
 }