I have a folder /common on an Ubuntu Server 22 host which is RW accessible by all users in group users i.e. user alice (with uid 1000) is a member of users (with gid 12345) and has fuull RW access to /common on the host.
On a KVM (also Ubuntu Server 22) on that host, I have the same user alice and group users with the same uid and gid respectively. The subuid and subgid (read from cat /etc/subuid and cat /etc/subgid) are different on both host and KVM.
I am sharing this folder from the Host to the KVM via virtiofs with the mount tag common-mount, using this entry in /etc/fstab:
common-mount /common virtiofs defaults 0 0
followed by sudo mount -a to mount the folder
However the mounted folder /common on that KVM is read-only to KVM user alice despite having the same uid and belonging to users. If I chmod 777 the folder /common on the host, that becomes accessible on the KVM, but I need chmod 775 for group RW-access and security.
Based on this link https://libvirt.org/kbase/virtiofs.html the differing subuid and subgid might be behind the issue, but when I made attempts to map them using idmap, the KVM became unbootable. If this relates to the solution, I am uncertain of the correct syntax.
