qapi: Convert simple union SocketAddressLegacy to flat one

Simple unions predate flat unions.  Having both complicates the QAPI
schema language and the QAPI generator.  We haven't been using simple
unions in new code for a long time, because they are less flexible and
somewhat awkward on the wire.

To prepare for their removal, convert simple union SocketAddressLegacy
to an equivalent flat one, with existing enum SocketAddressType
replacing implicit enum type SocketAddressLegacyKind.  Adds some
boilerplate to the schema, which is a bit ugly, but a lot easier to
maintain than the simple union feature.

Cc: "Daniel P. Berrangé" <berrange@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210917143134.412106-9-armbru@redhat.com>

chardev/char-socket.c

@@ -1520,7 +1520,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     addr = g_new0(SocketAddressLegacy, 1);
     if (path) {
         UnixSocketAddress *q_unix;
-        addr->type = SOCKET_ADDRESS_LEGACY_KIND_UNIX;
+        addr->type = SOCKET_ADDRESS_TYPE_UNIX;
         q_unix = addr->u.q_unix.data = g_new0(UnixSocketAddress, 1);
         q_unix->path = g_strdup(path);
 #ifdef CONFIG_LINUX
@@ -1530,7 +1530,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
         q_unix->abstract = abstract;
 #endif
     } else if (host) {
-        addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
+        addr->type = SOCKET_ADDRESS_TYPE_INET;
         addr->u.inet.data = g_new(InetSocketAddress, 1);
         *addr->u.inet.data = (InetSocketAddress) {
             .host = g_strdup(host),
@@ -1543,7 +1543,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
             .ipv6 = qemu_opt_get_bool(opts, "ipv6", 0),
         };
     } else if (fd) {
-        addr->type = SOCKET_ADDRESS_LEGACY_KIND_FD;
+        addr->type = SOCKET_ADDRESS_TYPE_FD;
         addr->u.fd.data = g_new(String, 1);
         addr->u.fd.data->str = g_strdup(fd);
     } else {

chardev/char-udp.c

@@ -165,7 +165,7 @@ static void qemu_chr_parse_udp(QemuOpts *opts, ChardevBackend *backend,
     qemu_chr_parse_common(opts, qapi_ChardevUdp_base(udp));
 
     addr = g_new0(SocketAddressLegacy, 1);
-    addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
+    addr->type = SOCKET_ADDRESS_TYPE_INET;
     addr->u.inet.data = g_new(InetSocketAddress, 1);
     *addr->u.inet.data = (InetSocketAddress) {
         .host = g_strdup(host),
@@ -180,7 +180,7 @@ static void qemu_chr_parse_udp(QemuOpts *opts, ChardevBackend *backend,
     if (has_local) {
         udp->has_local = true;
         addr = g_new0(SocketAddressLegacy, 1);
-        addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
+        addr->type = SOCKET_ADDRESS_TYPE_INET;
         addr->u.inet.data = g_new(InetSocketAddress, 1);
         *addr->u.inet.data = (InetSocketAddress) {
             .host = g_strdup(localaddr),

qapi/sockets.json

@@ -110,6 +110,38 @@
     'cid': 'str',
     'port': 'str' } }
 
+##
+# @InetSocketAddressWrapper:
+#
+# Since: 1.3
+##
+{ 'struct': 'InetSocketAddressWrapper',
+  'data': { 'data': 'InetSocketAddress' } }
+
+##
+# @UnixSocketAddressWrapper:
+#
+# Since: 1.3
+##
+{ 'struct': 'UnixSocketAddressWrapper',
+  'data': { 'data': 'UnixSocketAddress' } }
+
+##
+# @VsockSocketAddressWrapper:
+#
+# Since: 2.8
+##
+{ 'struct': 'VsockSocketAddressWrapper',
+  'data': { 'data': 'VsockSocketAddress' } }
+
+##
+# @StringWrapper:
+#
+# Since: 1.3
+##
+{ 'struct': 'StringWrapper',
+  'data': { 'data': 'String' } }
+
 ##
 # @SocketAddressLegacy:
 #
@@ -117,18 +149,18 @@
 #
 # Note: This type is deprecated in favor of SocketAddress.  The
 #       difference between SocketAddressLegacy and SocketAddress is that the
-#       latter is a flat union rather than a simple union. Flat is nicer
-#       because it avoids nesting on the wire, i.e. that form has fewer {}.
-
+#       latter is has fewer {} on the wire.
 #
 # Since: 1.3
 ##
 { 'union': 'SocketAddressLegacy',
+  'base': { 'type': 'SocketAddressType' },
+  'discriminator': 'type',
   'data': {
-    'inet': 'InetSocketAddress',
-    'unix': 'UnixSocketAddress',
-    'vsock': 'VsockSocketAddress',
-    'fd': 'String' } }
+    'inet': 'InetSocketAddressWrapper',
+    'unix': 'UnixSocketAddressWrapper',
+    'vsock': 'VsockSocketAddressWrapper',
+    'fd': 'StringWrapper' } }
 
 ##
 # @SocketAddressType:

tests/unit/test-yank.c

@@ -88,7 +88,7 @@ static void char_change_test(gconstpointer opaque)
             .type = CHARDEV_BACKEND_KIND_SOCKET,
             .u.socket.data = &(ChardevSocket) {
                 .addr = &(SocketAddressLegacy) {
-                    .type = SOCKET_ADDRESS_LEGACY_KIND_INET,
+                    .type = SOCKET_ADDRESS_TYPE_INET,
                     .u.inet.data = &addr->u.inet
                 },
                 .has_server = true,
@@ -102,7 +102,7 @@ static void char_change_test(gconstpointer opaque)
             .type = CHARDEV_BACKEND_KIND_UDP,
             .u.udp.data = &(ChardevUdp) {
                 .remote = &(SocketAddressLegacy) {
-                    .type = SOCKET_ADDRESS_LEGACY_KIND_UNIX,
+                    .type = SOCKET_ADDRESS_TYPE_UNIX,
                     .u.q_unix.data = &(UnixSocketAddress) {
                         .path = (char *)""
                     }
@@ -114,7 +114,7 @@ static void char_change_test(gconstpointer opaque)
             .type = CHARDEV_BACKEND_KIND_SOCKET,
             .u.socket.data = &(ChardevSocket) {
                 .addr = &(SocketAddressLegacy) {
-                    .type = SOCKET_ADDRESS_LEGACY_KIND_INET,
+                    .type = SOCKET_ADDRESS_TYPE_INET,
                     .u.inet.data = &(InetSocketAddress) {
                         .host = (char *)"127.0.0.1",
                         .port = (char *)"0"

util/qemu-sockets.c

@@ -1455,22 +1455,22 @@ SocketAddress *socket_address_flatten(SocketAddressLegacy *addr_legacy)
     addr = g_new(SocketAddress, 1);
 
     switch (addr_legacy->type) {
-    case SOCKET_ADDRESS_LEGACY_KIND_INET:
+    case SOCKET_ADDRESS_TYPE_INET:
         addr->type = SOCKET_ADDRESS_TYPE_INET;
         QAPI_CLONE_MEMBERS(InetSocketAddress, &addr->u.inet,
                            addr_legacy->u.inet.data);
         break;
-    case SOCKET_ADDRESS_LEGACY_KIND_UNIX:
+    case SOCKET_ADDRESS_TYPE_UNIX:
         addr->type = SOCKET_ADDRESS_TYPE_UNIX;
         QAPI_CLONE_MEMBERS(UnixSocketAddress, &addr->u.q_unix,
                            addr_legacy->u.q_unix.data);
         break;
-    case SOCKET_ADDRESS_LEGACY_KIND_VSOCK:
+    case SOCKET_ADDRESS_TYPE_VSOCK:
         addr->type = SOCKET_ADDRESS_TYPE_VSOCK;
         QAPI_CLONE_MEMBERS(VsockSocketAddress, &addr->u.vsock,
                            addr_legacy->u.vsock.data);
         break;
-    case SOCKET_ADDRESS_LEGACY_KIND_FD:
+    case SOCKET_ADDRESS_TYPE_FD:
         addr->type = SOCKET_ADDRESS_TYPE_FD;
         QAPI_CLONE_MEMBERS(String, &addr->u.fd, addr_legacy->u.fd.data);
         break;