On Mon, Jul 08, 2024 at 04:30:27PM +0200, Stefan Hajnoczi wrote:
> 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). It's time to QAPIfy QMP device_add!
>
> 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.
>
> 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 <arm...@redhat.com>
> Cc: Daniel P. Berrangé <berra...@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> system/qdev-monitor.c | 41 ++++++++++++++++++++++++++++-------------
> 1 file changed, 28 insertions(+), 13 deletions(-)
I think we're justified in saying that applications should have been
using the correct types already.
On the libvirt side we already switched to using JSON for -device,
which has forced us to ensure we're using the correct types. So
the risk of converting device_add is minimal from libvirt's POV.
Other non-libvirt mgmt apps might get tripped up. Fixing those
should not be too difficult and fixed code would remain compatible
with older QEMU versions too.
Reviewed-by: Daniel P. Berrangé <berra...@redhat.com>
>
> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> index 6af6ef7d66..1427aa173c 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
> @@ -872,8 +863,6 @@ 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));
> @@ -967,8 +956,34 @@ 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(OBJECT(dev));
> +out:
> hmp_handle_error(mon, err);
> }
>
> --
> 2.45.2
>
With regards,
Daniel
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