To keep the MCD JSON protocol separate from QMP, a custom monitor has been
implemented in mcd_monitor.c which can be run in parallel to the QMP monitor.
It is responsible for handling the JSON communication and for dispatching
the corresponding functions in mcd_stub.c
The MCD server stub will call the corresponding server functions.
To start the MCD monitor, configure QEMU with --enable-mcd and start it
with the -mcd option.
Signed-off-by: Mario Fleischmann <mario.fleischm...@lauterbach.com>
---
MAINTAINERS | 1 +
docs/interop/mcd.rst | 2 +
include/exec/mcdstub.h | 17 ++++++++
mcd/mcd_monitor.c | 89 ++++++++++++++++++++++++++++++++++++++++++
mcd/mcd_stub.c | 11 ++++++
mcd/meson.build | 4 +-
qemu-options.hx | 11 ++++++
system/vl.c | 13 ++++++
8 files changed, 147 insertions(+), 1 deletion(-)
create mode 100644 include/exec/mcdstub.h
create mode 100644 mcd/mcd_monitor.c
create mode 100644 mcd/mcd_stub.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 7c085dc..159a38f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3126,6 +3126,7 @@ S: Maintained
F: mcd/*
F: docs/interop/mcd.rst
F: qapi/mcd.json
+F: include/exec/mcdstub.h
Memory API
M: Paolo Bonzini <pbonz...@redhat.com>
diff --git a/docs/interop/mcd.rst b/docs/interop/mcd.rst
index 13e81df..860fa8d 100644
--- a/docs/interop/mcd.rst
+++ b/docs/interop/mcd.rst
@@ -52,6 +52,8 @@ has been added to implement a remote procedure call mechanism.
Each function within the API corresponds to one QAPI command, ensuring a
one-to-one mapping between the API's functions and the QAPI commands.
+Use the option ``-mcd dev`` to start MCD's QAPI monitor.
+
QAPI Reference
--------------
diff --git a/include/exec/mcdstub.h b/include/exec/mcdstub.h
new file mode 100644
index 0000000..0513616
--- /dev/null
+++ b/include/exec/mcdstub.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2025 Lauterbach GmbH
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#ifndef MCDSTUB_H
+#define MCDSTUB_H
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+
+bool mcd_monitor_start(const char *device, Error **errp);
+
+#endif /* MCDSTUB_H */
diff --git a/mcd/mcd_monitor.c b/mcd/mcd_monitor.c
new file mode 100644
index 0000000..7ee3eba
--- /dev/null
+++ b/mcd/mcd_monitor.c
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * mcdmonitor - MCD QAPI protocol handler
+ *
+ * Copyright (c) 2025 Lauterbach GmbH
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "exec/mcdstub.h"
+#include "qobject/qdict.h"
+#include "qobject/qjson.h"
+#include "mcd/mcd-qapi-init-commands.h"
+#include "mcd/mcd-qapi-commands.h"
+#include "monitor/monitor-internal.h"
+
+typedef struct {
+ Monitor mon;
+ JSONMessageParser parser;
+} MonitorMCD;
+
+static QmpCommandList qapi_commands;
+static MonitorMCD mcd_mon;
+
+static int mcd_monitor_can_read(void *opaque)
+{
+ return true;
+}
+
+static void mcd_monitor_read(void *opaque, const uint8_t *buf, int size)
+{
+ json_message_parser_feed(&mcd_mon.parser, (const char *) buf, size);
+}
+
+static void mcd_monitor_handle_chr_event(void *opaque, QEMUChrEvent event)
+{
+ switch (event) {
+ default:
+ /* Ignore */
+ break;
+ }
+}
+
+static void handle_mcd_command(void *opaque, QObject *req, Error *err)
+{
+ QDict *rsp = qmp_dispatch(&qapi_commands, req, false, &mcd_mon.mon);
+ const QObject *data = QOBJECT(rsp);
+ GString *json = qobject_to_json_pretty(data, false);
+ assert(json != NULL);
+ g_string_append_c(json, '\n');
+ monitor_puts(&mcd_mon.mon, json->str);
+ g_string_free(json, true);
+}
+
+static void mcd_monitor_init(Chardev *chr, Error **errp)
+{
+ if (!qemu_chr_fe_init(&mcd_mon.mon.chr, chr, errp)) {
+ return;
+ }
+ qemu_chr_fe_set_echo(&mcd_mon.mon.chr, true);
+
+ /* For now, don't use the I/O thread */
+ monitor_data_init(&mcd_mon.mon, true, false, false);
+
+ json_message_parser_init(&mcd_mon.parser, handle_mcd_command,
+ &mcd_mon.mon, NULL);
+
+ qemu_chr_fe_set_handlers(&mcd_mon.mon.chr, mcd_monitor_can_read,
+ mcd_monitor_read, mcd_monitor_handle_chr_event,
+ NULL, &mcd_mon.mon, NULL, true);
+}
+
+bool mcd_monitor_start(const char *device, Error **errp)
+{
+ Chardev *chr = qemu_chr_new_noreplay("mcd", device, true, NULL);
+ if (!chr) {
+ error_setg(errp, "mcdstub: couldn't create Chardev");
+ return false;
+ }
+ mcd_monitor_init(chr, errp);
+ return true;
+}
+
+static void __attribute__((__constructor__)) mcd_monitor_init_commands(void)
+{
+ mcd_qmp_init_marshal(&qapi_commands);
+}
diff --git a/mcd/mcd_stub.c b/mcd/mcd_stub.c
new file mode 100644
index 0000000..de679a4
--- /dev/null
+++ b/mcd/mcd_stub.c
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * mcdstub - Conversion of MCD QAPI requests to MCD server function calls
+ *
+ * Copyright (c) 2025 Lauterbach GmbH
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "mcd_api.h"
diff --git a/mcd/meson.build b/mcd/meson.build
index d62a625..191f0cc 100644
--- a/mcd/meson.build
+++ b/mcd/meson.build
@@ -28,7 +28,9 @@ mcd_ss = ss.source_set()
mcd_ss.add(mcd_qapi_files.to_list())
mcd_ss.add(files(
- 'mcd_server.c'))
+ 'mcd_server.c',
+ 'mcd_stub.c',
+ 'mcd_monitor.c'))
mcd_ss = mcd_ss.apply({})
diff --git a/qemu-options.hx b/qemu-options.hx
index dc694a9..2164ad3 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4724,6 +4724,17 @@ SRST
(see the :ref:`GDB usage` chapter in the System Emulation Users Guide).
ERST
+
+#ifdef CONFIG_MCD
+DEF("mcd", HAS_ARG, QEMU_OPTION_mcd, \
+ "-mcd dev accept MCD connection on 'dev'\n",
+ QEMU_ARCH_ALL)
+SRST
+``-mcd dev``
+ Start the MCD QAPI monitor and accept connections on device 'dev'.
+ERST
+#endif
+
DEF("d", HAS_ARG, QEMU_OPTION_d, \
"-d item1,... enable logging of specified items (use '-d help' for a
list of log items)\n",
QEMU_ARCH_ALL)
diff --git a/system/vl.c b/system/vl.c
index 520956f..73dc786 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -71,6 +71,9 @@
#include "system/numa.h"
#include "system/hostmem.h"
#include "exec/gdbstub.h"
+#ifdef CONFIG_MCD
+#include "exec/mcdstub.h"
+#endif
#include "gdbstub/enums.h"
#include "qemu/timer.h"
#include "chardev/char.h"
@@ -1280,6 +1283,7 @@ struct device_config {
DEV_PARALLEL, /* -parallel */
DEV_DEBUGCON, /* -debugcon */
DEV_GDB, /* -gdb, -s */
+ DEV_MCD, /* -mcd */
DEV_SCLP, /* s390 sclp */
} type;
const char *cmdline;
@@ -2789,6 +2793,10 @@ static bool qemu_machine_creation_done(Error **errp)
foreach_device_config_or_exit(DEV_GDB, gdbserver_start);
+#ifdef CONFIG_MCD
+ foreach_device_config_or_exit(DEV_MCD, mcd_monitor_start);
+#endif
+
if (!vga_interface_created && !default_vga &&
vga_interface_type != VGA_NONE) {
warn_report("A -vga option was passed but this machine "
@@ -3150,6 +3158,11 @@ void qemu_init(int argc, char **argv)
case QEMU_OPTION_gdb:
add_device_config(DEV_GDB, optarg);
break;
+#ifdef CONFIG_MCD
+ case QEMU_OPTION_mcd:
+ add_device_config(DEV_MCD, optarg);
+ break;
+#endif
case QEMU_OPTION_L:
if (is_help_option(optarg)) {
list_data_dirs = true;
--
2.34.1
