unable to read symlinks when mounting 9p filesystem with security_model=mapped

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1831354
Reported by 'Olie Hilt' on 2019-06-02 :

I am trying to use clang that is mounted from a 9p filesystem that has the
options
 -fsdev local,id=virtfs3,path=/clang,security_model=mapped-file -device
virtio-9p-pci,fsdev=virtfs3,mount_tag=clang

clang has symlinks to clang-9. eg /clang/clang/bin/clang is a symlink that
points to clang-9 in the current directory.

the clang filesystem is on a bind mount point on /clang/clang on the host
and this is mapped to the same place on the guest. If I have the same
virtfs mount point with the security_model=none I don't have this problem.