Hi Wei, I wanted to summarize the differences between the vhost-pci and virtio-vhost-user approaches because previous discussions may have been confusing.
vhost-pci defines a new virtio device type for each vhost device type (net, scsi, blk). It therefore requires a virtio device driver for each device type inside the slave VM. Adding a new device type requires: 1. Defining a new virtio device type in the VIRTIO specification. 3. Implementing a new QEMU device model. 2. Implementing a new virtio driver. virtio-vhost-user is a single virtio device that acts as a vhost-user protocol transport for any vhost device type. It requires one virtio driver inside the slave VM and device types are implemented using existing vhost-user slave libraries (librte_vhost in DPDK and libvhost-user in QEMU). Adding a new device type to virtio-vhost-user involves: 1. Adding any new vhost-user protocol messages to the QEMU virtio-vhost-user device model. 2. Adding any new vhost-user protocol messages to the vhost-user slave library. 3. Implementing the new device slave. The simplest case is when no new vhost-user protocol messages are required for the new device. Then all that's needed for virtio-vhost-user is a device slave implementation (#3). That slave implementation will also work with AF_UNIX because the vhost-user slave library hides the transport (AF_UNIX vs virtio-vhost-user). Even better, if another person has already implemented that device slave to use with AF_UNIX then no new code is needed for virtio-vhost-user support at all! If you compare this to vhost-pci, it would be necessary to design a new virtio device, implement it in QEMU, and implement the virtio driver. Much of virtio driver is more or less the same thing as the vhost-user device slave but it cannot be reused because the vhost-user protocol isn't being used by the virtio device. The result is a lot of duplication in DPDK and other codebases that implement vhost-user slaves. The way that vhost-pci is designed means that anyone wishing to support a new device type has to become a virtio device designer. They need to map vhost-user protocol concepts to a new virtio device type. This will be time-consuming for everyone involved (e.g. the developer, the VIRTIO community, etc). The virtio-vhost-user approach stays at the vhost-user protocol level as much as possible. This way there are fewer concepts that need to be mapped by people adding new device types. As a result, it will allow virtio-vhost-user to keep up with AF_UNIX vhost-user and grow because it's easier to work with. What do you think? Stefan
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