[PATCH v3 1/2] qdev-monitor: avoid QemuOpts in QMP device_add

[Stefan Hajnoczi <stefanha@redhat.com>]

The QMP device_add monitor command converts the QDict arguments to
QemuOpts and then back again to QDict. This process only supports scalar
types. Device properties like virtio-blk-pci's iothread-vq-mapping (an
array of objects) are silently dropped by qemu_opts_from_qdict() during
the QemuOpts conversion even though QAPI is capable of validating them.
As a result, hotplugging virtio-blk-pci devices with the
iothread-vq-mapping property does not work as expected (the property is
ignored).

Get rid of the QemuOpts conversion in qmp_device_add() and call
qdev_device_add_from_qdict() with from_json=true. Using the QMP
command's QDict arguments directly allows non-scalar properties.

The HMP is also adjusted since qmp_device_add()'s now expects properly
typed JSON arguments and cannot be used from HMP anymore. Move the code
that was previously in qmp_device_add() (with QemuOpts conversion and
from_json=false) into hmp_device_add() so that its behavior is
unchanged.

This patch changes the behavior of QMP device_add but not HMP
device_add. QMP clients that sent incorrectly typed device_add QMP
commands no longer work. This is a breaking change but clients should be
using the correct types already. See the netdev_add QAPIfication in
commit db2a380c8457 for similar reasoning and object-add in commit
9151e59a8b6e. Unlike those commits, we continue to rely on 'gen': false
for the time being.

Markus helped me figure this out and even provided a draft patch. The
code ended up very close to what he suggested.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 system/qdev-monitor.c | 44 ++++++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 15 deletions(-)

diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
index 6af6ef7d66..26404f314d 100644
--- a/system/qdev-monitor.c
+++ b/system/qdev-monitor.c
@@ -849,18 +849,9 @@ void hmp_info_qdm(Monitor *mon, const QDict *qdict)
 
 void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
 {
-    QemuOpts *opts;
     DeviceState *dev;
 
-    opts = qemu_opts_from_qdict(qemu_find_opts("device"), qdict, errp);
-    if (!opts) {
-        return;
-    }
-    if (!monitor_cur_is_qmp() && qdev_device_help(opts)) {
-        qemu_opts_del(opts);
-        return;
-    }
-    dev = qdev_device_add(opts, errp);
+    dev = qdev_device_add_from_qdict(qdict, true, errp);
     if (!dev) {
         /*
          * Drain all pending RCU callbacks. This is done because
@@ -872,11 +863,8 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
          * to the user
          */
         drain_call_rcu();
-
-        qemu_opts_del(opts);
-        return;
     }
-    object_unref(OBJECT(dev));
+    object_unref(dev);
 }
 
 static DeviceState *find_device_state(const char *id, Error **errp)
@@ -967,8 +955,34 @@ void qmp_device_del(const char *id, Error **errp)
 void hmp_device_add(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
+    QemuOpts *opts;
+    DeviceState *dev;
 
-    qmp_device_add((QDict *)qdict, NULL, &err);
+    opts = qemu_opts_from_qdict(qemu_find_opts("device"), qdict, &err);
+    if (!opts) {
+        goto out;
+    }
+    if (qdev_device_help(opts)) {
+        qemu_opts_del(opts);
+        return;
+    }
+    dev = qdev_device_add(opts, &err);
+    if (!dev) {
+        /*
+         * Drain all pending RCU callbacks. This is done because
+         * some bus related operations can delay a device removal
+         * (in this case this can happen if device is added and then
+         * removed due to a configuration error)
+         * to a RCU callback, but user might expect that this interface
+         * will finish its job completely once qmp command returns result
+         * to the user
+         */
+        drain_call_rcu();
+
+        qemu_opts_del(opts);
+    }
+    object_unref(dev);
+out:
     hmp_handle_error(mon, err);
 }
 
-- 
2.46.0