migration: New QAPI type 'MigrateAddress'

This patch introduces well defined MigrateAddress struct
and its related child objects.

The existing argument of 'migrate' and 'migrate-incoming' QAPI
- 'uri' is of type string. The current implementation follows
double encoding scheme for fetching migration parameters like
'uri' and this is not an ideal design.

Motive for intoducing struct level design is to prevent double
encoding of QAPI arguments, as Qemu should be able to directly
use the QAPI arguments without any level of encoding.

Note: this commit only adds the type, and actual uses comes
in later commits.

Fabiano fixed for "file" transport.

Suggested-by: Aravind Retnakaran <aravind.retnakaran@nutanix.com>
Signed-off-by: Het Gala <het.gala@nutanix.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231023182053.8711-2-farosas@suse.de>
Message-Id: <20231023182053.8711-3-farosas@suse.de>

qapi/migration.json

@@ -1584,6 +1584,63 @@
 ##
 { 'command': 'migrate-continue', 'data': {'state': 'MigrationStatus'} }
 
+##
+# @MigrationAddressType:
+#
+# The migration stream transport mechanisms.
+#
+# @socket: Migrate via socket.
+#
+# @exec: Direct the migration stream to another process.
+#
+# @rdma: Migrate via RDMA.
+#
+# @file: Direct the migration stream to a file.
+#
+# Since 8.2
+##
+{ 'enum': 'MigrationAddressType',
+  'data': [ 'socket', 'exec', 'rdma', 'file' ] }
+
+##
+# @FileMigrationArgs:
+#
+# @filename: The file to receive the migration stream
+#
+# @offset: The file offset where the migration stream will start
+#
+# Since 8.2
+##
+{ 'struct': 'FileMigrationArgs',
+  'data': { 'filename': 'str',
+            'offset': 'uint64' } }
+
+##
+# @MigrationExecCommand:
+#
+# @args: command (list head) and arguments to execute.
+#
+# Since 8.2
+##
+{ 'struct': 'MigrationExecCommand',
+  'data': {'args': [ 'str' ] } }
+
+##
+# @MigrationAddress:
+#
+# Migration endpoint configuration.
+#
+# Since 8.2
+##
+{ 'union': 'MigrationAddress',
+  'base': { 'transport' : 'MigrationAddressType'},
+  'discriminator': 'transport',
+  'data': {
+    'socket': 'SocketAddress',
+    'exec': 'MigrationExecCommand',
+    'rdma': 'InetSocketAddress',
+    'file': 'FileMigrationArgs' } }
+
 ##
 # @migrate:
 #