In vhost-user protocol we have VHOST_USER_BACKEND_CONFIG_CHANGE_MSG, which backend may send to notify Qemu, that we should re-read the config, and notify the guest.
Still that's not always convenient: backend may not support this message. Also, having QMP command to force config sync is more reliable than waiting for notification from external program. It also may be helpful for debug/restore: if we have changed disk size, but guest doesn't see that, it's good to have a separate QMP command to trigger resync of the config. So, the series proposes two experimental APIs: 1. x-device-sync-config command, to trigger config synchronization 2. X_CONFIG_READ event, which notify management tool that guest read the updated config. Of course, that can't guarantee that the guest correctly handled the updated config, but it's still better than nothing: for sure guest will not show new disk size until it read the updated config. So, management tool may wait for this event to report success to the user. The series is based on "[PATCH v8 0/4] pci hotplug tracking": it doesn't depend on it, but just modify same files, so I just to avoid extra conflicts. Based-on: <20231005092926.56231-1-vsement...@yandex-team.ru> Vladimir Sementsov-Ogievskiy (4): vhost-user-blk: simplify and fix vhost_user_blk_handle_config_change qapi: introduce device-sync-config qapi: device-sync-config: check runstate qapi: introduce CONFIG_READ event hw/block/vhost-user-blk.c | 32 ++++++++++++++--------- hw/virtio/virtio-pci.c | 18 +++++++++++++ include/hw/qdev-core.h | 3 +++ include/monitor/qdev.h | 1 + include/sysemu/runstate.h | 1 + monitor/monitor.c | 1 + qapi/qdev.json | 36 ++++++++++++++++++++++++++ softmmu/qdev-monitor.c | 53 +++++++++++++++++++++++++++++++++++++++ softmmu/runstate.c | 5 ++++ 9 files changed, 138 insertions(+), 12 deletions(-) -- 2.34.1
