virtiofs在DAX之上，guest通过vfs到达fuse，fuse到virtio-fs前端，virtio-fs前端通过dax操作内存

使用DAX后，virtiofsd主要负责一些metadata ops相关的操作，比如trunc file之类的

参考资料

https://kernel.taobao.org/2019/11/virtio-fs-intro-and-perf-optimize/ ※

https://virtio-fs.gitlab.io/design.html ※

https://lwn.net/Articles/774495/

https://virtio-fs.gitlab.io/

https://gitlab.com/virtio-fs

https://virtio-fs.gitlab.io/howto-qemu.html

https://lwn.net/Articles/813807/