VirtIO-fs using writeback cache seems very broken at the moment. If a
guest accesses a file (even just using 'touch'), that the host is
currently writing, the guest can permanently end up with a truncated
version of that file. Even subsequent operations like moving the file,
will not result in the correct file being visible, but just rename the
truncated one.
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Add support for sharing directories with a guest VM.
virtio-fs needs virtiofsd to be started. In order to start virtiofsd
as a process (despite being a daemon it is does not run in the
background), a double-fork is used.
virtiofsd should close itself together with QEMU.
There are the parameters dirid and the optional parameters direct-io,
cache and writeback. Additionally the expose-xattr & expose-acl
parameter can be set to expose xattr & acl settings from the shared
filesystem to the guest system.
The dirid gets mapped to the path on the current node and is also used
as a mount tag (name used to mount the device on the guest).
example config:
```
virtiofs0: foo,direct-io=1,cache=always,expose-acl=1
virtiofs1: dirid=bar,cache=never,expose-xattr=1,writeback=1
```
For information on the optional parameters see the coherent doc patch
and the official gitlab README:
https://gitlab.com/virtio-fs/virtiofsd/-/blob/main/README.md
Also add a permission check for virtiofs directory access.
Add virtiofsd to the Recommends list for the qemu-server Debian
package, this allows users to opt-out of installing this package, e.g.
for certification reasons.
Signed-off-by: Markus Frank <m.frank@proxmox.com>
Link: https://lore.proxmox.com/20250407134950.265270-3-m.frank@proxmox.com
Tested-by: Lukas Wagner <l.wagner@proxmox.com>
[TL: squash d/control change and re-add Lukas' T-b, as nothing
essentially changed from the v16 where his tag applied]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
