KVM Forum 2021

Planning the design of an emulated device in QEMU can be a daunting task and it can be hard to gain an upfront overview of how to proceed with wiring up a new device. In the context of the emulated NVMe device, this talk aims to present such an overview. The QEMU 6.0 release represents a milestone for the emulated NVMe device and add support for a number of advanced features such as multipath I/O and namespace sharing, metadata and data integrity. The implementation of these features require the use of many internal QEMU features and some were initially used incorrectly, causing frustration to developers and users alike. The focal point of this talk is the lessons learned in regard to QDev and the QEMU Object Model, asynchronous I/O, mistakes that were made, and how these are rectified. Finally, this talk will take the opportunity to suggest the idea of using the device as a thin simulator for measuring latencies in host software and drivers. The emulating (and not simulating) nature of QEMU posits several interesting challenges and members of the audience with any experience in this field are encouraged to pitch in and provide feedback on the viability of the ideas presented.