I have a system running Centos 7 with the stock qemu/KVM code. I have several virtual servers running on this system and would like to enable the filesystem passthrough option. So far, I have not had any luck. I have downloaded ther kernel sources from Kernel.org and compiled with all the 9p / 9p2000 modules installed, but the option "Filesystem" option is still greyed out in Virt-Manager with the message "not supported for this hypervisor/libvirt combination". I have tried Centos 6, 7 and Ubuntu 14.04 as guest OS, and none of these seems to help.
Is there any way to fix this issue? I would gladly recompile qemu/libvirtd to fix the issue if it can be done safely without breaking anything. (I have had bad luck compiling things under Centos in the past. The paths don't seem to be what the source expects and things get put in the wrong places.)