qdev-monitor: avoid QemuOpts in QMP device_add

qdev-monitor: avoid QemuOpts in QMP device_add

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>
Message-ID: <20240827192751.948633-2-stefanha@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>