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Description of problem: Filesystem passthrough "virtio-9pfs" support in KVM is not implemented in RHEL7 Version-Release number of selected component (if applicable): 7+ How reproducible: NA Steps to Reproduce: 1. NA 2. 3. Actual results: NA Expected results: NA Additional info: See https://access.redhat.com/discussions/1119043 Virt-Manager and probably most of libvirt still support device definition with no warning. There is no mention of this at libvirt.org. the user finds out only after configuring a filesystem and then getting a "mount: unknown filesystem type '9p'" in the guest and undertaking research. This may be old news but it is frustrating.
This is not a bug, in RHEL-7 the filesystem passthrough was disabled because 9p is not reliable. You can find more information in the discussion that you've provided as additional info. Virt-manager in RHEL-7 correctly prints message "Not supported for this hypervisor/libvirt combination." if you try to add a new filesystem device. There was a bug to disable 9p in RHEL-7 bug 1077172.