sockets: add ability to disable DNS resolution for InetSocketAddress

Add a 'numeric' flag to the InetSocketAddress struct to allow the
caller to indicate that DNS should be skipped for the host/port
fields. This is useful if the caller knows the address is already
numeric and wants to guarantee no (potentially blocking) DNS
lookups are attempted.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

qapi-schema.json

@@ -3983,6 +3983,10 @@
 #
 # @port: port part of the address, or lowest port if @to is present
 #
+# @numeric: #optional true if the host/port are guaranteed to be numeric,
+#           false if name resolution should be attempted. Defaults to false.
+#           (Since 2.9)
+#
 # @to: highest port to try
 #
 # @ipv4: whether to accept IPv4 addresses, default try both IPv4 and IPv6
@@ -3997,6 +4001,7 @@
   'data': {
     'host': 'str',
     'port': 'str',
+    '*numeric':  'bool',
     '*to': 'uint16',
     '*ipv4': 'bool',
     '*ipv6': 'bool' } }

util/qemu-sockets.c

@@ -38,6 +38,10 @@
 # define AI_V4MAPPED 0
 #endif
 
+#ifndef AI_NUMERICSERV
+# define AI_NUMERICSERV 0
+#endif
+
 
 static int inet_getport(struct addrinfo *e)
 {
@@ -141,6 +145,9 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
 
     memset(&ai,0, sizeof(ai));
     ai.ai_flags = AI_PASSIVE;
+    if (saddr->has_numeric && saddr->numeric) {
+        ai.ai_flags |= AI_NUMERICHOST | AI_NUMERICSERV;
+    }
     ai.ai_family = inet_ai_family_from_address(saddr, &err);
     ai.ai_socktype = SOCK_STREAM;