Re: [dpdk-dev] [RFC v1 0/2] Add device emulation support in DPDK

[Thomas Monjalon <thomas@monjalon.net>]

14/08/2020 21:16, Chenbo Xia:
> Background & Motivation
> -----------------------
> In order to reduce the attack surface, QEMU community is disaggregating QEMU by
> removing part of device emulation from it. The disaggregated/multi-process QEMU
> is using VFIO-over-socket/vfio-user as the main transport mechanism to disaggregate
> I/O services from QEMU[2]. Vfio-user essentially implements the VFIO device model
> presented to the user process by a set of messages over a unix-domain socket. The
> main difference between application using vfio-user and application using vfio
> kernel module is that device manipulation is based on socket messages for vfio-user
> but system calls for vfio kernel module. The vfio-user devices consist of a generic
> VFIO device type, living in QEMU, which is called the client[3], and the core device
> implementation (emulated device), living outside of QEMU, which is called the server.
> 
> With the introduction and support of vfio-user in QEMU, QEMU is explicitly adding
> support for external emulated device and data path. We are trying to leverage that
> and introducing vfio-user support in DPDK. By doing so, DPDK is enabled to be an
> alternative I/O device emulation library of building virtualized devices along with
> high-performance data path in separate processes outside QEMU. It will be easy for
> hardware vendors to provide virtualized solutions of their hardware devices by
> implementing emulated device in DPDK.
> 
> Except for vfio-user introduced in DPDK, this series also introduces the first
> emulated device implementation. That is emulated AVF device (avf_emudev) implemented
> by AVF emulation driver (avf_emudev driver). Emulated AVF device demos how emulated
> device could be implemented in DPDK. SPDK is also investigating to implement use case
> for NVMe. 

I am completely unaware of this change in QEMU.
I've found this presentation about Multi-process QEMU by Oracle:
	https://static.sched.com/hosted_files/kvmforum2019/d2/kvm-mpqemu.pdf
and there is the wiki page you already referenced:
	https://wiki.qemu.org/Features/MultiProcessQEMU

I guess virtio stays inside QEMU?
What is really moving out? e1000, ne2000 and vmxnet3?
Why emulated AVF is needed, compared to a simple VFIO passthrough?