[libvirt PATCHv3 04/12] docs: add virtiofs kbase

Daniel P. Berrangé berrange at redhat.com
Mon Feb 3 16:17:31 UTC 2020


On Thu, Jan 30, 2020 at 06:06:20PM +0100, Ján Tomko wrote:
> Add a document describing the usage of virtiofs.
> ---
>  docs/kbase.html.in      |   3 +
>  docs/kbase/virtiofs.rst | 152 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 155 insertions(+)
>  create mode 100644 docs/kbase/virtiofs.rst
> 
> diff --git a/docs/kbase.html.in b/docs/kbase.html.in
> index c156414c41..7d6caf3cb1 100644
> --- a/docs/kbase.html.in
> +++ b/docs/kbase.html.in
> @@ -29,6 +29,9 @@
>          <dt><a href="kbase/backing_chains.html">Backing chain management</a></dt>
>          <dd>Explanation of how disk backing chain specification impacts libvirt's
>            behaviour and basic troubleshooting steps of disk problems.</dd>
> +
> +        <dt><a href="kbase/virtiofs.html">Virtio-FS</a></dt>
> +        <dd>Share a filesystem between the guest and the host</dd>
>        </dl>
>      </div>
>  
> diff --git a/docs/kbase/virtiofs.rst b/docs/kbase/virtiofs.rst
> new file mode 100644
> index 0000000000..e76ff8ca4b
> --- /dev/null
> +++ b/docs/kbase/virtiofs.rst
> @@ -0,0 +1,152 @@
> +============================
> +Sharing files with Virtio-FS
> +============================
> +
> +=== 8< delete before merging 8< ===
> +NOTE: if you're looking at this note, this is just a proposal.
> +See the up-to-date version on: https://libvirt.org/kbase/virtiofs.html
> +=== 8< --------------------- 8< ===

...this shouldn't be here still

> +
> +.. contents::
> +
> +=========
> +Virtio-FS
> +=========
> +
> +Virtio-FS is a shared file system that lets virtual machines access
> +a directory tree on the host. Unlike existing approaches, it
> +is designed to offer local file system semantics and performance.
> +
> +See https://virtio-fs.gitlab.io/
> +
> +==========
> +Host setup
> +==========
> +
> +The host-side virtiofsd daemon, like other vhost-user backed devices,
> +requres shared memory between the host and the guest. As of QEMU 4.2, this

requires

> +requires specifying a NUMA topology for the guest and explicitly specifying
> +a memory backend. Multiple options are available:
> +
> +Either of the following:
> +
> +\a) Use file-backed memory

Why are you disabling list-ification here & throughout the file ?

> +
> +Configure the directory where the files backing the memory will be stored
> +with the ``memory_backing_dir`` option in ``/etc/libvirt/qemu.conf``
> +
> +::
> +
> +   # This directory is used for memoryBacking source if configured as file.
> +   # NOTE: big files will be stored here
> +   memory_backing_dir = "/dev/shm/"
> +
> +\b) Use hugepage-backed memory
> +
> +Make sure there are enough huge pages allocated for the requested guest memory.
> +For example, for one guest with 2 GiB of RAM backed by 2 MiB hugepages:
> +
> +::
> +
> +   # virsh allocpages 2M 1024


I'm not understanding from this how big the files will be for
virtiofsd ?  How much memory should users expect to be needed
per-guest per-virtiofsd ?



Regards,
Daniel
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