mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
synced 2024-11-05 03:21:13 +00:00
a3342bdb25
Now that our CI has transitioned from ClearLinux to Ubuntu images exclusively, let's update the documentation to refer to Ubuntu images instead of ClearLinux's ones. Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
89 lines
4.2 KiB
Markdown
89 lines
4.2 KiB
Markdown
# How to use virtio-fs
|
|
|
|
In the context of virtualization, it is always convenient to be able to share a directory from the host with the guest.
|
|
|
|
__virtio-fs__, also known as __vhost-user-fs__ is a virtual device defined by the VIRTIO specification which allows any VMM to perform filesystem sharing.
|
|
|
|
## Pre-requisites
|
|
|
|
### The daemon
|
|
|
|
This virtual device relies on the _vhost-user_ protocol, which assumes the backend (device emulation) is handled by a dedicated process running on the host. This daemon is called __virtiofsd__ and needs to be present on the host.
|
|
|
|
_Build virtiofsd_
|
|
```bash
|
|
git clone --depth 1 "https://github.com/sboeuf/qemu.git" -b "virtio-fs" $VIRTIOFSD_DIR
|
|
cd $VIRTIOFSD_DIR
|
|
./configure --prefix=$PWD --target-list=x86_64-softmmu
|
|
make virtiofsd -j `nproc`
|
|
sudo setcap cap_sys_admin+epi "virtiofsd"
|
|
```
|
|
_Create shared directory_
|
|
```bash
|
|
mkdir /tmp/shared_dir
|
|
```
|
|
_Run virtiofsd_
|
|
```bash
|
|
./virtiofsd \
|
|
-d \
|
|
--socket-path=/tmp/virtiofs \
|
|
-o source=/tmp/shared_dir \
|
|
-o cache=none
|
|
```
|
|
|
|
The `cache=none` option should be the default when using `virtiofsd` with the __cloud-hypervisor__ VMM. This prevents from using the guest page cache, which reduces the memory footprint of the guest. When running multiple virtual machines on the same host, this will let the host deal with page cache, which will increase the density of virtual machines which can be launched.
|
|
|
|
The `cache=always` option will allow for the guest page cache to be used, which will increase the memory footprint of the guest. This option should be used only for specific use cases where a single VM is going to be running on a host.
|
|
|
|
### The kernel
|
|
|
|
In order to leverage __virtio-fs__ support from within the guest, and because the code has not been merged in upstream Linux kernel yet, it is required to build a custom kernel embedding the patches.
|
|
|
|
The following branch `virtio-fs-virtio-iommu` on the repository https://github.com/cloud-hypervisor/linux.git includes all the needed patches to support __virtio-fs__.
|
|
|
|
Make sure to build a kernel out of this branch that can be then used to boot the VM.
|
|
|
|
## How to share directories with cloud-hypervisor
|
|
|
|
### Start the VM
|
|
Once the daemon is running, the option `--fs` from __cloud-hypervisor__ needs to be used.
|
|
|
|
Direct kernel boot option is preferred since we need to provide the custom kernel including the __virtio-fs__ patches. We could boot from `hypervisor-fw` if we had previously edited the image to replace the kernel binary.
|
|
|
|
Because _vhost-user_ expects a dedicated process (__virtiofsd__ in this case) to be able to access the guest RAM to communicate through the _virtqueues_ with the driver running in the guest, `--memory` option needs to be slightly modified. It needs to specify a backing file for the memory so that an external process can access it.
|
|
|
|
Assuming you have `focal-server-cloudimg-amd64.raw` and `custom-vmlinux.bin` on your system, here is the __cloud-hypervisor__ command you need to run:
|
|
```bash
|
|
./cloud-hypervisor \
|
|
--cpus 4 \
|
|
--memory "size=512,file=/dev/shm" \
|
|
--disk path=focal-server-cloudimg-amd64.raw \
|
|
--kernel custom-vmlinux.bin \
|
|
--cmdline "console=ttyS0 console=hvc0 root=/dev/vda1 rw" \
|
|
--fs tag=myfs,socket=/tmp/virtiofs,num_queues=1,queue_size=512
|
|
```
|
|
|
|
By default, DAX is enabled with a cache window of 8GiB. You can specify a custom size (let's say 4GiB for this example) for the cache by explicitly setting DAX and the cache size:
|
|
|
|
```bash
|
|
--fs tag=virtiofs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=on,cache_size=4G
|
|
|
|
```
|
|
|
|
In case you don't want to use a shared window of cache to pass the shared files content, this means you will have to explicitly disable DAX with `dax=off`. Note that in this case, the `cache_size` parameter will be ignored.
|
|
|
|
```bash
|
|
--fs tag=virtiofs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=off
|
|
|
|
```
|
|
|
|
### Mount the shared directory
|
|
The last step is to mount the shared directory inside the guest, using the `virtiofs` filesystem type.
|
|
```bash
|
|
mkdir mount_dir
|
|
mount -t virtiofs -o dax myfs mount_dir/
|
|
```
|
|
The `tag` needs to be consistent with what has been provided through the __cloud-hypervisor__ command line, which happens to be `myfs` in this example.
|
|
|
|
The `-o dax` option must be removed in case the shared cache region is not enabled from the VMM.
|