LookingGlass/module/README.md

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

### 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:

```xml
<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, in `/etc/apparmor.d/abstractions/libvirt-qemu`, append:

    # 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