[PATCH v3 1/6] accel: Introduce 'query-accels' QMP command

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Introduce the 'query-accels' QMP command which returns a list
of built-in accelerator names.

- Accelerator is a QAPI enum of all existing accelerators,

- AcceleratorInfo is a QAPI structure providing accelerator
  specific information. Currently the common structure base
  provides the name of the accelerator, while the specific
  part is empty, but each accelerator can expand it.

- 'query-accels' QMP command returns a list of @AcceleratorInfo

For example on a KVM-only build we get:

    { "execute": "query-accels" }
    {
        "return": [
            {
                "name": "qtest"
            },
            {
                "name": "kvm"
            }
        ]
    }

Note that we can't make the enum values or union branches conditional
because of target-specific poisoning of accelerator definitions.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Since v2: @since 6.0 -> 6.1, added note (Eric)
Since v1: 'type' -> 'name' in comments
---
 qapi/machine.json | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 accel/accel-qmp.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 accel/meson.build |  2 +-
 3 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 accel/accel-qmp.c

diff --git a/qapi/machine.json b/qapi/machine.json
index 6e90d463fc9..4babc06f8b0 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1274,3 +1274,52 @@
 ##
 { 'event': 'MEM_UNPLUG_ERROR',
   'data': { 'device': 'str', 'msg': 'str' } }
+
+##
+# @Accelerator:
+#
+# An enumeration of accelerator names.
+#
+# Since: 6.1
+##
+{ 'enum': 'Accelerator',
+  'data': [ 'qtest', 'tcg', 'kvm', 'hax', 'hvf', 'whpx', 'xen' ] }
+
+##
+# @AcceleratorInfo:
+#
+# Accelerator information.
+#
+# @name: The accelerator name.
+#
+# Since: 6.1
+##
+{ 'union': 'AcceleratorInfo',
+  'base': {'name': 'Accelerator'},
+  'discriminator': 'name',
+  'data': { } }
+
+##
+# @query-accels:
+#
+# Get a list of AcceleratorInfo for all built-in accelerators.
+#
+# Returns: a list of @AcceleratorInfo describing each accelerator.
+#
+# Since: 6.1
+#
+# Example:
+#
+# -> { "execute": "query-accels" }
+# <- { "return": [
+#        {
+#            "name": "qtest"
+#        },
+#        {
+#            "name": "kvm"
+#        }
+#    ] }
+#
+##
+{ 'command': 'query-accels',
+  'returns': ['AcceleratorInfo'] }
diff --git a/accel/accel-qmp.c b/accel/accel-qmp.c
new file mode 100644
index 00000000000..426737b3f9a
--- /dev/null
+++ b/accel/accel-qmp.c
@@ -0,0 +1,49 @@
+/*
+ * QEMU accelerators, QMP commands
+ *
+ * Copyright (c) 2021 Red Hat Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/qapi-commands-machine.h"
+
+static const bool accel_builtin_list[ACCELERATOR__MAX] = {
+    [ACCELERATOR_QTEST] = true,
+#ifdef CONFIG_TCG
+    [ACCELERATOR_TCG] = true,
+#endif
+#ifdef CONFIG_KVM
+    [ACCELERATOR_KVM] = true,
+#endif
+#ifdef CONFIG_HAX
+    [ACCELERATOR_HAX] = true,
+#endif
+#ifdef CONFIG_HVF
+    [ACCELERATOR_HVF] = true,
+#endif
+#ifdef CONFIG_WHPX
+    [ACCELERATOR_WHPX] = true,
+#endif
+#ifdef CONFIG_XEN_BACKEND
+    [ACCELERATOR_XEN] = true,
+#endif
+};
+
+AcceleratorInfoList *qmp_query_accels(Error **errp)
+{
+    AcceleratorInfoList *list = NULL, **tail = &list;
+
+    for (Accelerator accel = 0; accel < ACCELERATOR__MAX; accel++) {
+        if (accel_builtin_list[accel]) {
+            AcceleratorInfo *info = g_new0(AcceleratorInfo, 1);
+
+            info->name = accel;
+
+            QAPI_LIST_APPEND(tail, info);
+        }
+    }
+
+    return list;
+}
diff --git a/accel/meson.build b/accel/meson.build
index b44ba30c864..7a48f6d568d 100644
--- a/accel/meson.build
+++ b/accel/meson.build
@@ -1,4 +1,4 @@
-specific_ss.add(files('accel-common.c'))
+specific_ss.add(files('accel-common.c', 'accel-qmp.c'))
 softmmu_ss.add(files('accel-softmmu.c'))
 user_ss.add(files('accel-user.c'))
 
-- 
2.26.3