haiwei-li / ivshmem_example

A kernel module and corresponding user application that use ivshmem to communicate between VMs

Ivshmem-example

This repo demostrate the usage of qemu ivshmem pci device.

What is ivshmem

The Inter-VM shared memory device (ivshmem) is designed to share a memory region between multiple QEMU processes running different guests and the host. In order for all guests to be able to pick up the shared memory area, it is modeled by QEMU as a PCI device exposing said memory to the guest as a PCI BAR.

Specification: see here

How to use it

This project is using qemu version > 2.5.0, so the revision of ivshmem is 1, I have not try with the older version, but I believe it should work, you just need pass some different options to qemu

Server setup

1. run ivshmem server: ivshmem-server -vF -n 2 make it run in verbose and foreground mode and set the number of msi vector to 2. (Using default n = 1 is enough, but I just want to try with more vectors, in this project, only vector 1 get used)

2. open two virtual machines with option -device ivshmem-doorbell,vectors=2,chardev=ivshmem -chardev socket,path=/tmp/ivshmem_socket,id=ivshmem

Kernel module setup

In two virtual machines, setup the kernel module:

1. sudo insmod ivshmem.ko
2. Using dmsg command to read the device major number
3. Create the char device sudo mknod /dev/ivshmem c <major_nr> 0

User space application

Use ./userctl

• -d read the guest id
• on one of the vm, run sudo ./userctl -p
• on the other vm, run sudo ./userctl -c <destination_guest_id>