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 ChardevBackend to
an equivalent flat one.  Adds some boilerplate to the schema, which is
a bit ugly, but a lot easier to maintain than the simple union
feature.

Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210917143134.412106-8-armbru@redhat.com>
---
 qapi/char.json | 187 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 165 insertions(+), 22 deletions(-)

diff --git a/qapi/char.json b/qapi/char.json
index 9b18ee3305..cc1e455c87 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -407,39 +407,182 @@
   'base': 'ChardevCommon',
   'if': 'CONFIG_SPICE_PROTOCOL' }
 
+##
+# @ChardevBackendKind:
+#
+# @pipe: Since 1.5
+# @udp: Since 1.5
+# @mux: Since 1.5
+# @msmouse: Since 1.5
+# @wctablet: Since 2.9
+# @braille: Since 1.5
+# @testdev: Since 2.2
+# @stdio: Since 1.5
+# @console: Since 1.5
+# @spicevmc: Since 1.5
+# @spiceport: Since 1.5
+# @qemu-vdagent: Since 6.1
+# @vc: v1.5
+# @ringbuf: Since 1.6
+# @memory: Since 1.5
+#
+# Since: 1.4
+##
+{ 'enum': 'ChardevBackendKind',
+  'data': [ 'file',
+            'serial',
+            'parallel',
+            'pipe',
+            'socket',
+            'udp',
+            'pty',
+            'null',
+            'mux',
+            'msmouse',
+            'wctablet',
+            'braille',
+            'testdev',
+            'stdio',
+            'console',
+            { 'name': 'spicevmc', 'if': 'CONFIG_SPICE' },
+            { 'name': 'spiceport', 'if': 'CONFIG_SPICE' },
+            { 'name': 'qemu-vdagent', 'if': 'CONFIG_SPICE_PROTOCOL' },
+            'vc',
+            'ringbuf',
+            # next one is just for compatibility
+            'memory' ] }
+
+##
+# @ChardevFileWrapper:
+#
+# Since: 1.4
+##
+{ 'struct': 'ChardevFileWrapper',
+  'data': { 'data': 'ChardevFile' } }
+
+##
+# @ChardevHostdevWrapper:
+#
+# Since: 1.4
+##
+{ 'struct': 'ChardevHostdevWrapper',
+  'data': { 'data': 'ChardevHostdev' } }
+
+##
+# @ChardevSocketWrapper:
+#
+# Since: 1.4
+##
+{ 'struct': 'ChardevSocketWrapper',
+  'data': { 'data': 'ChardevSocket' } }
+
+##
+# @ChardevUdpWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevUdpWrapper',
+  'data': { 'data': 'ChardevUdp' } }
+
+##
+# @ChardevCommonWrapper:
+#
+# Since: 2.6
+##
+{ 'struct': 'ChardevCommonWrapper',
+  'data': { 'data': 'ChardevCommon' } }
+
+##
+# @ChardevMuxWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevMuxWrapper',
+  'data': { 'data': 'ChardevMux' } }
+
+##
+# @ChardevStdioWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevStdioWrapper',
+  'data': { 'data': 'ChardevStdio' } }
+
+##
+# @ChardevSpiceChannelWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevSpiceChannelWrapper',
+  'data': { 'data': 'ChardevSpiceChannel' } }
+
+##
+# @ChardevSpicePortWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevSpicePortWrapper',
+  'data': { 'data': 'ChardevSpicePort' } }
+
+##
+# @ChardevQemuVDAgentWrapper:
+#
+# Since: 6.1
+##
+{ 'struct': 'ChardevQemuVDAgentWrapper',
+  'data': { 'data': 'ChardevQemuVDAgent' } }
+
+##
+# @ChardevVCWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevVCWrapper',
+  'data': { 'data': 'ChardevVC' } }
+
+##
+# @ChardevRingbufWrapper:
+#
+# Since: 1.5
+##
+{ 'struct': 'ChardevRingbufWrapper',
+  'data': { 'data': 'ChardevRingbuf' } }
+
 ##
 # @ChardevBackend:
 #
 # Configuration info for the new chardev backend.
 #
-# Since: 1.4 (testdev since 2.2, wctablet since 2.9, vdagent since 6.1)
+# Since: 1.4
 ##
 { 'union': 'ChardevBackend',
-  'data': { 'file': 'ChardevFile',
-            'serial': 'ChardevHostdev',
-            'parallel': 'ChardevHostdev',
-            'pipe': 'ChardevHostdev',
-            'socket': 'ChardevSocket',
-            'udp': 'ChardevUdp',
-            'pty': 'ChardevCommon',
-            'null': 'ChardevCommon',
-            'mux': 'ChardevMux',
-            'msmouse': 'ChardevCommon',
-            'wctablet': 'ChardevCommon',
-            'braille': 'ChardevCommon',
-            'testdev': 'ChardevCommon',
-            'stdio': 'ChardevStdio',
-            'console': 'ChardevCommon',
-            'spicevmc': { 'type': 'ChardevSpiceChannel',
+  'base': { 'type': 'ChardevBackendKind' },
+  'discriminator': 'type',
+  'data': { 'file': 'ChardevFileWrapper',
+            'serial': 'ChardevHostdevWrapper',
+            'parallel': 'ChardevHostdevWrapper',
+            'pipe': 'ChardevHostdevWrapper',
+            'socket': 'ChardevSocketWrapper',
+            'udp': 'ChardevUdpWrapper',
+            'pty': 'ChardevCommonWrapper',
+            'null': 'ChardevCommonWrapper',
+            'mux': 'ChardevMuxWrapper',
+            'msmouse': 'ChardevCommonWrapper',
+            'wctablet': 'ChardevCommonWrapper',
+            'braille': 'ChardevCommonWrapper',
+            'testdev': 'ChardevCommonWrapper',
+            'stdio': 'ChardevStdioWrapper',
+            'console': 'ChardevCommonWrapper',
+            'spicevmc': { 'type': 'ChardevSpiceChannelWrapper',
                           'if': 'CONFIG_SPICE' },
-            'spiceport': { 'type': 'ChardevSpicePort',
+            'spiceport': { 'type': 'ChardevSpicePortWrapper',
                            'if': 'CONFIG_SPICE' },
-            'qemu-vdagent': { 'type': 'ChardevQemuVDAgent',
+            'qemu-vdagent': { 'type': 'ChardevQemuVDAgentWrapper',
                               'if': 'CONFIG_SPICE_PROTOCOL' },
-            'vc': 'ChardevVC',
-            'ringbuf': 'ChardevRingbuf',
+            'vc': 'ChardevVCWrapper',
+            'ringbuf': 'ChardevRingbufWrapper',
             # next one is just for compatibility
-            'memory': 'ChardevRingbuf' } }
+            'memory': 'ChardevRingbufWrapper' } }
 
 ##
 # @ChardevReturn:
-- 
2.31.1