Allow to allocate cache manager with custom refill socket

Cache managers use two sockets: one for cache refill operation,
and another one for notifications.

In order to simulate NETLINK events by reading data from files,
we need to be able to overwrite callbacks for both sockets.

This new function allows us to set up refill socket any way we want.
It does have requirement that the refill socket be blocking.

include/netlink/cache.h

@@ -146,6 +146,10 @@ struct nl_cache_mngr;
 extern int			nl_cache_mngr_alloc(struct nl_sock *,
 						    int, int,
 						    struct nl_cache_mngr **);
+extern int			nl_cache_mngr_alloc_ex(struct nl_sock *,
+							struct nl_sock *,
+						    int, int,
+						    struct nl_cache_mngr **);
 extern int			nl_cache_mngr_add(struct nl_cache_mngr *,
 						  const char *,
 						  change_func_t,

lib/cache_mngr.c

@@ -148,6 +148,33 @@ static int event_input(struct nl_msg *msg, void *arg)
  */
 int nl_cache_mngr_alloc(struct nl_sock *sk, int protocol, int flags,
 			struct nl_cache_mngr **result)
+{
+	struct nl_sock *sk_blocking = nl_socket_alloc();
+	int err;
+
+	if (!sk_blocking) {
+		return -NLE_NOMEM;
+	}
+	if ((err = nl_connect(sk_blocking, protocol)) < 0) {
+			nl_socket_free(sk_blocking);
+			return err;
+	}
+	return nl_cache_mngr_alloc_ex(sk, sk_blocking, protocol, flags, result);
+}
+
+/**
+ * Allocate new cache manager, with custom callback on refill socket
+ * @arg sk		Netlink socket or NULL to auto allocate
+ * @arg sk_blocking		Blocking Netlink socket for cache refills
+ * @arg protocol	Netlink protocol this manager is used for
+ * @arg flags		Flags (\c NL_AUTO_PROVIDE)
+ * @arg result		Result pointer
+ *
+ * Same as \f nl_cache_mngr_alloc, but sets custom refill socket
+ * Note: ownership of the sk_blocking passes to the cache manager
+ */
+int nl_cache_mngr_alloc_ex(struct nl_sock *sk, struct nl_sock *sk_blocking, int protocol, int flags,
+			struct nl_cache_mngr **result)
 {
 	struct nl_cache_mngr *mngr;
 	int err = -NLE_NOMEM;
@@ -156,10 +183,18 @@ int nl_cache_mngr_alloc(struct nl_sock *sk, int protocol, int flags,
 	if (flags & NL_ALLOCATED_SOCK)
 		BUG();
 
+	if(!sk_blocking) {
+		BUG();
+	}
+
 	mngr = calloc(1, sizeof(*mngr));
-	if (!mngr)
+	if (!mngr) {
+		// No manager yet, to free it in case of error
+		nl_socket_free(sk_blocking);
 		return -NLE_NOMEM;
+	}
 
+	mngr->cm_sync_sock = sk_blocking;
 	if (!sk) {
 		if (!(sk = nl_socket_alloc()))
 			goto errout;
@@ -185,23 +220,13 @@ int nl_cache_mngr_alloc(struct nl_sock *sk, int protocol, int flags,
 	if ((err = nl_socket_set_nonblocking(mngr->cm_sock)) < 0)
 		goto errout;
 
-	/* Create and allocate socket for sync cache fills */
-	mngr->cm_sync_sock = nl_socket_alloc();
-	if (!mngr->cm_sync_sock) {
-		err = -NLE_NOMEM;
-		goto errout;
-	}
-	if ((err = nl_connect(mngr->cm_sync_sock, protocol)) < 0)
-		goto errout_free_sync_sock;
 
 	NL_DBG(1, "Allocated cache manager %p, protocol %d, %d caches\n",
 	       mngr, protocol, mngr->cm_nassocs);
 
 	*result = mngr;
 	return 0;
 
-errout_free_sync_sock:
-	nl_socket_free(mngr->cm_sync_sock);
 errout:
 	nl_cache_mngr_free(mngr);
 	return err;

libnl-3.sym

@@ -79,6 +79,7 @@ global:
 	nl_cache_mngr_add;
 	nl_cache_mngr_add_cache;
 	nl_cache_mngr_alloc;
+	nl_cache_mngr_alloc_ex;
 	nl_cache_mngr_data_ready;
 	nl_cache_mngr_free;
 	nl_cache_mngr_get_fd;