From ec57de02c7ef512438f5a01ce7805a21388aa244 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Wed, 30 Apr 2025 11:33:38 +0200
Subject: [PATCH] socket: open IPv6 socket by default if IPv4 is disabled

When no remote and local address is specified, and IPv4 is disabled by
the -6 option, open an IPv6 socket. This is used by the Linux-specific
timestamping configuration and socket option checking. It enables
operation on a system that has no support for IPv4 sockets.
---
 socket.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/socket.c b/socket.c
index 78e54fa..d08b865 100644
--- a/socket.c
+++ b/socket.c
@@ -212,13 +212,25 @@ get_reusable_socket(int type, IPSockAddr *spec)
 
 /* ================================================== */
 
+static int
+get_default_inet_domain(void)
+{
+#ifdef FEAT_IPV6
+  if (!ip4_enabled && ip6_enabled)
+    return AF_INET6;
+#endif
+  return AF_INET;
+}
+
+/* ================================================== */
+
 #if defined(SOCK_CLOEXEC) || defined(SOCK_NONBLOCK)
 static int
 check_socket_flag(int sock_flag, int fd_flag, int fs_flag)
 {
   int sock_fd, fd_flags, fs_flags;
 
-  sock_fd = socket(AF_INET, SOCK_DGRAM | sock_flag, 0);
+  sock_fd = socket(get_default_inet_domain(), SOCK_DGRAM | sock_flag, 0);
   if (sock_fd < 0)
     return 0;
 
@@ -526,7 +538,7 @@ open_ip_socket(IPSockAddr *remote_addr, IPSockAddr *local_addr, const char *ifac
   else if (remote_addr)
     family = remote_addr->ip_addr.family;
   else
-    family = IPADDR_INET4;
+    family = !ip4_enabled && ip6_enabled ? IPADDR_INET6 : IPADDR_INET4;
 
   switch (family) {
     case IPADDR_INET4: