Introduce event-loop-base abstract class

Introduce the 'event-loop-base' abstract class, it'll hold the
properties common to all event loops and provide the necessary hooks for
their creation and maintenance. Then have iothread inherit from it.

EventLoopBaseClass is defined as user creatable and provides a hook for
its children to attach themselves to the user creatable class 'complete'
function. It also provides an update_params() callback to propagate
property changes onto its children.

The new 'event-loop-base' class will live in the root directory. It is
built on its own using the 'link_whole' option (there are no direct
function dependencies between the class and its children, it all happens
trough 'constructor' magic). And also imposes new compilation
dependencies:

    qom <- event-loop-base <- blockdev (iothread.c)

And in subsequent patches:

    qom <- event-loop-base <- qemuutil (util/main-loop.c)

All this forced some amount of reordering in meson.build:

 - Moved qom build definition before qemuutil. Doing it the other way
   around (i.e. moving qemuutil after qom) isn't possible as a lot of
   core libraries that live in between the two depend on it.

 - Process the 'hw' subdir earlier, as it introduces files into the
   'qom' source set.

No functional changes intended.

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20220425075723.20019-2-nsaenzju@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/qapi/qom.json b/qapi/qom.json
index eeb5395ff3..a2439533c5 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -500,6 +500,20 @@
             '*grab-toggle': 'GrabToggleKeys' } }
 
 ##
+# @EventLoopBaseProperties:
+#
+# Common properties for event loops
+#
+# @aio-max-batch: maximum number of requests in a batch for the AIO engine,
+#                 0 means that the engine will use its default.
+#                 (default: 0)
+#
+# Since: 7.1
+##
+{ 'struct': 'EventLoopBaseProperties',
+  'data': { '*aio-max-batch': 'int' } }
+
+##
 # @IothreadProperties:
 #
 # Properties for iothread objects.
@@ -516,17 +530,15 @@
 #               algorithm detects it is spending too long polling without
 #               encountering events. 0 selects a default behaviour (default: 0)
 #
-# @aio-max-batch: maximum number of requests in a batch for the AIO engine,
-#                 0 means that the engine will use its default
-#                 (default:0, since 6.1)
+# The @aio-max-batch option is available since 6.1.
 #
 # Since: 2.0
 ##
 { 'struct': 'IothreadProperties',
+  'base': 'EventLoopBaseProperties',
   'data': { '*poll-max-ns': 'int',
             '*poll-grow': 'int',
-            '*poll-shrink': 'int',
-            '*aio-max-batch': 'int' } }
+            '*poll-shrink': 'int' } }
 
 ##
 # @MemoryBackendProperties: