[PATCH v8 02/12] 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"
            }
        ]
    }

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
v8:
- Include code snippet from Markus adding to machine-target.json
  to be able to use enum values or union branches conditional.
- Use accel_find() on enum to be sure the accelerator is enabled
  at runtime (chat with jsnow / eblake).

Cc: Eric Blake <eblake@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
---
 qapi/machine-target.json | 54 ++++++++++++++++++++++++++++++++++++++++
 accel/accel-qmp.c        | 32 ++++++++++++++++++++++++
 accel/meson.build        |  2 +-
 3 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 accel/accel-qmp.c

diff --git a/qapi/machine-target.json b/qapi/machine-target.json
index e7811654b72..586a61b5d99 100644
--- a/qapi/machine-target.json
+++ b/qapi/machine-target.json
@@ -329,3 +329,57 @@
 ##
 { 'command': 'query-cpu-definitions', 'returns': ['CpuDefinitionInfo'],
   'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_I386) || defined(TARGET_S390X) || defined(TARGET_MIPS)' }
+
+##
+# @Accelerator:
+#
+# An enumeration of accelerator names.
+#
+# Since: 6.1
+##
+{ 'enum': 'Accelerator',
+  'data': [
+      { 'name': 'hax', 'if': 'defined(CONFIG_HAX)' },
+      { 'name': 'hvf', 'if': 'defined(CONFIG_HVF)' },
+      { 'name': 'kvm', 'if': 'defined(CONFIG_KVM)' },
+      { 'name': 'qtest' },
+      { 'name': 'tcg', 'if': 'defined(CONFIG_TCG)' },
+      { 'name': 'whpx', 'if': 'defined(CONFIG_WHPX)' },
+      { 'name': 'xen', 'if': 'defined(CONFIG_XEN_BACKEND)' } ] }
+
+##
+# @AcceleratorInfo:
+#
+# Accelerator information.
+#
+# @name: The accelerator name.
+#
+# Since: 6.1
+##
+{ 'struct': 'AcceleratorInfo',
+  'data': { 'name': 'Accelerator' } }
+
+##
+# @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..0098297caa5
--- /dev/null
+++ b/accel/accel-qmp.c
@@ -0,0 +1,32 @@
+/*
+ * QEMU accelerators, QMP commands
+ *
+ * Copyright (c) 2021 Red Hat Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/accel.h"
+#include "qapi/qapi-types-machine-target.h"
+#include "qapi/qapi-commands-machine-target.h"
+
+AcceleratorInfoList *qmp_query_accels(Error **errp)
+{
+    AcceleratorInfoList *list = NULL, **tail = &list;
+
+    for (Accelerator accel = 0; accel < ACCELERATOR__MAX; accel++) {
+        AcceleratorInfo *info;
+
+        if (!accel_find(Accelerator_str(accel))) {
+            /* Accelerator available at build time but not at runtime. */
+            continue;
+        }
+
+        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