Kernel Module

This kernel module implements a basic interface to the IVSHMEM device for LookingGlass when using LookingGlass in VM->VM mode.

Additionally, in VM->host mode, it can be used to generate a shared memory device on the host machine that supports dmabuf.

Compiling (Manual)

Make sure you have your kernel headers installed first, on Debian/Ubuntu use the following command:

apt-get install linux-headers-$(uname -r)

Then simply run make and you’re done.

Loading

For VM->VM mode, simply run:

insmod kvmfr.ko

For VM->host mode with dmabuf, instead of creating a shared memory file, load this module with the parameter static_size_mb. For example, a 128 MB shared memory device can be created with:

insmod kvmfr.ko static_size_mb=128

Multiple devices can be created by separating the sizes with commas. For example, static_size_mb=128,64 would create two kvmfr devices: kvmfr0 would be 128 MB and kvmfr1 would be 64 MB.

Compiling & Installing (DKMS)

You can install this module into DKMS so that it persists across kernel upgrades. Simply run:

dkms install .

Loading

For VM->VM, simply modprobe the module:

modprobe kvmfr

For VM->host with dmabuf, modprobe with the parameter static_size_mb:

modprobe kvmfr static_size_mb=128

Just like above, multiple devices can be created by separating the sizes with commas.

Usage

This will create the /dev/kvmfr0 node that represents the KVMFR interface. To use the interface you need permission to access it by either creating a udev rule to ensure your user can read and write to it, or simply change its ownership manually, ie:

sudo chown user:user /dev/kvmfr0

An example udev rule, which you can put in /etc/udev/rules.d/99-kvmfr.rules, is (replace user with your username):

SUBSYSTEM=="kvmfr", OWNER="user", GROUP="kvm", MODE="0660"

Usage with looking glass is simple, you only need to specify the path to the device node, for example:

./looking-glass-client -f /dev/kvmfr0

You may also use a config file: ~/.looking-glass-client.ini, or /etc/looking-glass-client.ini.

[app]
shmFile=/dev/kvmfr0

VM->Host

In VM->host mode, use this device in place of the shared memory file.

For example, with qemu, you would use the following arguments:

-device ivshmem-plain,id=shmem0,memdev=looking-glass
-object memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=128M,share=yes

Note that the size argument must be the same size as what you passed to static_size_mb argument for the kernel module.

libvirt

With libvirt, you can use the following XML block:

<qemu:commandline>
  <qemu:arg value='-device'/>
  <qemu:arg value='ivshmem-plain,id=shmem0,memdev=looking-glass'/>
  <qemu:arg value='-object'/>
  <qemu:arg value='memory-backend-file,id=looking-glass,mem-path=/dev/kvmfr0,size=128M,share=yes'/>
</qemu:commandline>

Remember to add xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0' to the <domain>.

On certain distros, running libvirt this way poses issues with apparmor and cgroups.

For apparmor, create /etc/apparmor.d/local/abstractions/libvirt-qemu if it doesn’t exist, and add the following:

# Looking Glass
/dev/kvmfr0 rw,

For cgroups, in /etc/libvirt/qemu.conf, uncomment the cgroup_device_acl block and add /dev/kvmfr0 to the list. Then restart libvirtd:

sudo systemctl restart libvirtd.service

systemd-modules-load

For convenience, you may load the KVMFR module when starting your computer. We can use the systemd-modules-load.service(8) service for this task.

Create a file as /etc/modules-load.d/kvmfr.conf with the following contents:

#KVMFR Looking Glass module
kvmfr

This will now run the next time you start your machine.

If you are running in VM->host mode, you must additionally add another file in /etc/modprobe.d/kvmfr.conf to properly set the size. It should have the following contents, while adjusting static_size_mb to your needs:

#KVMFR Looking Glass module
options kvmfr static_size_mb=128