On Thu, Jan 23, 2020 at 18:46:11 +0100, Ján Tomko wrote: > Add a document describing the usage of virtiofs. > --- > docs/kbase.html.in | 3 + > docs/kbase/virtiofs.rst | 153 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 156 insertions(+) > create mode 100644 docs/kbase/virtiofs.rst The XML documentation added to formatdomain.html is really lacking. At the very least this document should be linked from there. > > 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..83351e0a28 > --- /dev/null > +++ b/docs/kbase/virtiofs.rst > @@ -0,0 +1,153 @@ > +============================ > +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< === > + > +.. contents:: > + > +========= > +Virtio-FS > +========= > + > +Virtio-FS is a delicious delicacy aiming to provide an easy-to-configure > +way of sharing filesystems between the host and the virtual machine. > + > +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 specifying a NUMA topology for the guest and explicitly specifying > +a memory backend. Multiple options are available: > + > +Either of the following: > + > +1. Use file-backed memory > + > +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/" > + > +2. Use hugepage-backed memory > + > +Make sure there are enough huge pages allocated for the requested guest memory. > +For exmaple, for one guest with 2 GiB of RAM backed by 2 MiB hugepages: > + > +:: > + > + # virsh allocpages 2M 1024 > + > +=========== > +Guest setup > +=========== > + > +1. Specify the NUMA topology > + > +in the domain XML of the guest. > +For the simplest one-node topology for a guest with 2GiB of RAM and 8 vCPUs: > + > +:: > + > + <domain> > + ... > + <cpu ...> > + <numa> > + <cell id='0' cpus='0-7' memory='2' unit='GiB' memAccess='shared'/> > + </numa> > + </cpu> > + ... > + </domain> > + > +Note that the CPU element might already be specified and only one is allowed. > + > +2. Specify the memory backend > + > +Either of the following: > + > +2.1. File-backed memory > + > +:: > + > + <domain> > + ... > + <memoryBacking> > + <access mode='shared'/> > + </memoryBacking> > + ... > + </domain> > + > +This will create a file in the directory specified in ``qemu.conf`` > + > +2.2. Hugepage-backed memory > + > +:: > + > + <domain> > + ... > + <memoryBacking> > + <hugepages> > + <page size='2' unit='M'/> > + </hugepages> > + <access mode='shared'/> > + </memoryBacking> > + ... > + </domain> > + > +3. Add the ``vhost-user-fs`` QEMU device via the ``filesystem`` element > + > +:: > + > + <domain> > + ... > + <devices> > + ... > + <filesystem type='mount' accessmode='passthrough'> > + <driver type='virtiofs'> > + <binary>/usr/libexec/virtiofsd</binary> > + </driver> > + <source dir='/path'/> > + <target dir='mount_tag'/> > + </filesystem> > + ... > + </devices> > + </domain> > + > +Note that despite its name, the ``target dir`` is actually a mount tag and does > +not have to correspond to the desired mount point in the guest. In that case it should perhaps also have a different attribute. > + > +So far, ``passthrough`` is the only supported access mode and it requires > +running the ``virtiofsd`` daemon as root. > + > +4. Boot the guest and mount the filesystem > + > +:: > + > + guest# mount -t virtiofs mount_tag /mnt/mount/path > + > +Note: this requires virtiofs support in the guest kernel (Linux v5.4 or later) > + > +=================== > +Optional parameters > +=================== > + > +More optional elements can be specified > + > +:: > + > + <driver type='virtiofs' queue='1024' xattr='on'> > + <binary>/usr/libexec/virtiofsd</binary> > + <cache mode='always' size='1024' unit='GiB'/> > + <lock posix_lock='on' flock='on'/> > + </driver> > -- > 2.21.0 >
