Signed-off-by: Markus Frank <m.fr...@proxmox.com> --- v14: * addressed formulation nits * added paragraph about expose-acl & expose-xattr
qm.adoc | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 97 insertions(+), 2 deletions(-) diff --git a/qm.adoc b/qm.adoc index 4bb8f2c..86b3877 100644 --- a/qm.adoc +++ b/qm.adoc @@ -1202,6 +1202,100 @@ recommended to always use a limiter to avoid guests using too many host resources. If desired, a value of '0' for `max_bytes` can be used to disable all limits. +[[qm_virtiofs]] +Virtio-fs +~~~~~~~~~ + +Virtio-fs is a shared filesystem designed for virtual environments. It allows to +share a directory tree available on the host by mounting it within VMs. It does +not use the network stack and aims to offer similar performance and semantics as +the source filesystem. + +To use virtio-fs, the https://gitlab.com/virtio-fs/virtiofsd[virtiofsd] daemon +needs to run in the background. This happens automatically in {pve} when +starting a VM using a virtio-fs mount. + +Linux VMs with kernel >=5.4 support virtio-fs by default. + +There is a guide available on how to utilize virtio-fs in Windows VMs. +https://github.com/virtio-win/kvm-guest-drivers-windows/wiki/Virtiofs:-Shared-file-system + +Known Limitations +^^^^^^^^^^^^^^^^^ + +* If virtiofsd crashes, its mount point will hang in the VM until the VM +is completely stopped. +* virtiofsd not responding may result in a hanging mount in the VM, similar to +an unreachable NFS. +* Memory hotplug does not work in combination with virtio-fs (also results in +hanging access). +* Memory related features such as live migration, snapshots, and hibernate are +not available with virtio-fs devices. +* Windows cannot understand ACLs in the context of virtio-fs. Therefore, do not +expose ACLs for Windows VMs, otherwise the virtio-fs device will not be +visible within the VM. + +Add Mapping for Shared Directories +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +To add a mapping for a shared directory, you can use the API directly with +`pvesh` as described in the xref:resource_mapping[Resource Mapping] section: + +---- +pvesh create /cluster/mapping/dir --id dir1 \ + --map node=node1,path=/path/to/share1 \ + --map node=node2,path=/path/to/share2,announce-submounts=1 \ +---- + +Set `announce-submounts` to `1` if multiple filesystems are mounted in a shared +directory. This tells the guest which directories are mount points to prevent +data loss/corruption. With `announce-submounts`, virtiofsd reports a different +device number for each submount it encounters. Without it, duplicates may be +created because inode IDs are only unique on a single filesystem. + +Add virtio-fs to a VM +^^^^^^^^^^^^^^^^^^^^^ + +To share a directory using virtio-fs, add the parameter `virtiofs<N>` (N can be +anything between 0 and 9) to the VM config and use a directory ID (dirid) that +has been configured in the resource mapping. Additionally, you can set the +`cache` option to either `always`, `never`, or `auto` (default: `auto`), +depending on your requirements. How the different caching modes behave can be +read at https://lwn.net/Articles/774495/ under the "Caching Modes" section. To +enable writeback cache set `writeback` to `1`. + +Virtiofsd supports ACL and xattr passthrough (can be enabled with the +`expose-acl` and `expose-xattr` options), allowing the guest to access ACLs and +xattrs if the underlying host filesystem supports them, but they must also be +compatible with the guest filesystem (for example most Linux filesystems support +ACLs, while Windows filesystems do not). + +The `expose-acl` option automatically implies `expose-xattr`, that is, it makes +no difference if you set `expose-xattr` to `0` if `expose-acl` is set to `1`. + +If you want virtio-fs to honor the `O_DIRECT` flag, you can set the `direct-io` +parameter to `1` (default: `0`). This will degrade performance, but is useful if +applications do their own caching. + +---- +qm set <vmid> -virtiofs0 dirid=<dirid>,cache=always,direct-io=1 +qm set <vmid> -virtiofs1 <dirid>,cache=never,expose-xattr=1 +qm set <vmid> -virtiofs2 <dirid>,expose-acl=1,writeback=1 +---- + +To mount virtio-fs in a guest VM with the Linux kernel virtio-fs driver, run the +following command inside the guest: + +---- +mount -t virtiofs <mount tag> <mount point> +---- + +The dirid associated with the path on the current node is also used as the mount +tag (name used to mount the device on the guest). + +For more information on available virtiofsd parameters, see the +https://gitlab.com/virtio-fs/virtiofsd[GitLab virtiofsd project page]. + [[qm_bootorder]] Device Boot Order ~~~~~~~~~~~~~~~~~ @@ -1885,8 +1979,9 @@ in the relevant tab in the `Resource Mappings` category, or on the cli with [thumbnail="screenshot/gui-datacenter-mapping-pci-edit.png"] -Where `<type>` is the hardware type (currently either `pci` or `usb`) and -`<options>` are the device mappings and other configuration parameters. +Where `<type>` is the hardware type (currently either `pci`, `usb` or +xref:qm_virtiofs[dir]) and `<options>` are the device mappings and other +configuration parameters. Note that the options must include a map property with all identifying properties of that hardware, so that it's possible to verify the hardware did -- 2.39.5 _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
