[Bug 294383] p9fs(4): mount fails in QEMU/KVM guest

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294383

            Bug ID: 294383
           Summary: p9fs(4): mount fails in QEMU/KVM guest
           Product: Base System
           Version: 16.0-CURRENT
          Hardware: powerpc
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: [email protected]
          Reporter: [email protected]

using:

FreeBSD 16.0-CURRENT FreeBSD 16.0-CURRENT #1: Fri Apr 10 09:45:03 BST 2026
[email protected]:/build/obj/bsd/src/bsd/main/powerpc.powerpc64/sys/GENERIC64
powerpc

(src 82ff1c334b97e5b68e6330e90f0aa6ae0f6af9aa)

under QEMU 10.1.3 with a virtio-9p-pci share defined:

qemu-system-ppc64 -accel kvm -nographic -serial mon:stdio \
  -drive 'file=/vm/ppc64-main/root.img,format=raw' \
  -smp 'cpus=8' -M pseries -m 8g \
  -netdev 'tap,id=net0,ifname=vm-ppc64-main,script=no,downscript=no' \
  -device 'virtio-net-pci,netdev=net0' \
  -fsdev local,id=vmshare,security_model=passthrough,path=/export/vmshare \
  -device virtio-9p-pci,fsdev=vmshare,mount_tag=vmshare

the guest detects the share:

Autoloading module: virtio_p9fs
virtio_p9fs0: <VirtIO 9P Transport> numa-domain 0 on virtio_pci0
virtio_p9fs0: Mount tag: vmshare

but trying to mount the share fails with:

root@ppc64-main:~ # mount -t p9fs vmshare /mnt
qemu-system-ppc64: Failed to decode VirtFS request type 100

(note, the second line is printed by qemu on the host.)

mount(8) then hangs and the terminal is unresponsive.

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