Is there a way to execute a long-standing QMP command outside of the BQL? The situation we're seeing is a slow query-block due to a slow system call (fstat over NFS) causing the main thread to spend too long holding the global mutex and locking up the vcpu thread when it goes out of the guest for MMIO.
The call chain for QMP is: qmp_query_block bdrv_query_info bdrv_block_device_info bdrv_query_image_info bdrv_do_query_node_info bdrv_get_allocated_file_size bdrv_poll_co <- Waiting with qemu_global_mutex locked [coroutine] bdrv_co_get_allocated_file_size_entry bdrv_co_get_allocated_file_size raw_co_get_allocated_file_size fstat <- SLOW! The closest I got was moving the coroutine into a separate iothread, unlocking the global mutex and releasing the bdrv aio_context around aio_poll. It feels wrong though because we're technically still operating on the block state but not holding the context. Is there a more standard way if doing this? Is it possible at all? Thanks
