Kernel version 6.3 adds support for sending the user supplementary groups (Bug 2134128):

https://lore.kernel.org/lkml/Y%2FzYyN7NeLKusmSj@miu.piliscsaba.redhat.com/#r

The current version of virtiofsd only implements a workaround to this problem.
It keeps CAP_DAC_OVERRIDE after switching uid/gid (Bug 2141629), but this trick doesn't work over NFS or CephFS. This is also required to fix https://issues.redhat.com/browse/KATA-1776

How reproducible:
100%

Steps to Reproduce:
1. start virtiofsd over a NFS shared dir
root# virtiofsd --shared-dir=/.../some_nfs_shared_dir ...

2. start the guest.

3. (in guest) mount the virtiofs
root#  mount -t virtiofs myfs /mnt

4. (in guest) add a user and it to the wheel group (as supplementary group)
root# useradd u1
root# passwd u1
root# usermod -G wheel u1

5. (in guest) as root, create a test directory
root# mkdir -m 0770 testdir
root# chgrp wheel testdir

6. (in guest) switch to u1 user and try to create a file inside the test directory
root# su u1
u1$ touch testdir/file


Actual results:
fails with "Permission denied"

Expected results:
# ls -l testdir/file 
-rw-r--r-- 1 user user 0 nov 10 11:12 testdir/file