[Pkg-rust-maintainers] Bug#1144114: virtiofsd: Fails to mount with "vhost_backend_init failed: Protocol error"

[Simon John]

Package: virtiofsd
Version: 1.14.0-2
Severity: important

Dear Maintainer,

After upgrading from 1.14.0-1 which works fine, to 1.14.0-2, I can now 
not mount any virtiofs shares on Sid (tried on 2 different Trixie guests).

Error from virt-manager:

Error starting domain: internal error: QEMU unexpectedly closed the monitor
(vm='debian13'): 2026-08-11T10:15:39.842604Z qemu-system-x86_64: -device
{"driver":"vhost-user-fs-pci","id":"fs0","chardev":"chr-vu-
fs0","tag":"kernel","bus":"pci.2","addr":"0x0"}: Failed to read msg header.
Read 0 instead of 12. Original request 0.
2026-08-11T10:15:39.842685Z qemu-system-x86_64: -device 
{"driver":"vhost-user-
fs-pci","id":"fs0","chardev":"chr-vu-
fs0","tag":"kernel","bus":"pci.2","addr":"0x0"}: vhost_backend_init failed:
Protocol error

Traceback (most recent call last):
   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 67, in
cb_wrapper
     callback(asyncjob, *args, **kwargs)
     ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
   File "/usr/share/virt-manager/virtManager/asyncjob.py", line 101, in 
tmpcb
     callback(*args, **kwargs)
     ~~~~~~~~^^^^^^^^^^^^^^^^^
   File "/usr/share/virt-manager/virtManager/object/libvirtobject.py", 
line 57,
in newfn
     ret = fn(self, *args, **kwargs)
   File "/usr/share/virt-manager/virtManager/object/domain.py", line 
1446, in
startup
     self._backend.create()
     ~~~~~~~~~~~~~~~~~~~~^^
   File "/usr/lib/python3/dist-packages/libvirt.py", line 1401, in create
     raise libvirtError('virDomainCreate() failed')
libvirt.libvirtError: internal error: QEMU unexpectedly closed the monitor
(vm='debian13'): 2026-08-11T10:15:39.842604Z qemu-system-x86_64: -device
{"driver":"vhost-user-fs-pci","id":"fs0","chardev":"chr-vu-
fs0","tag":"kernel","bus":"pci.2","addr":"0x0"}: Failed to read msg header.
Read 0 instead of 12. Original request 0.
2026-08-11T10:15:39.842685Z qemu-system-x86_64: -device 
{"driver":"vhost-user-
fs-pci","id":"fs0","chardev":"chr-vu-
fs0","tag":"kernel","bus":"pci.2","addr":"0x0"}: vhost_backend_init failed:
Protocol error

Or on the CLI:

$ virsh attach-device debian13  virtiofs-kernel.xml --live

error: Failed to attach device from virtiofs-kernel.xml
error: internal error: unable to execute QEMU command 'device_add':
vhost_backend_init failed: Protocol error

Here's my virtiofs-kernel.xml:

<filesystem type="mount" accessmode="passthrough">
   <driver type="virtiofs"/>
   <binary path="/usr/libexec/virtiofsd"/>
   <idmap>
     <uid start="502" target="502" count="1"/>
     <gid start="502" target="502" count="1"/>
   </idmap>
   <source dir="/home/simon/kernel"/>
   <target dir="kernel"/>
</filesystem>

I've not changed anything else and downgrading to 1.14.0-1 works fine again.


-- System Information:
Debian Release: forky/sid
   APT prefers unstable
   APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 7.1.7+deb14-amd64 (SMP w/32 CPU threads; PREEMPT)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_GB:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages virtiofsd depends on:
ii  libc6        2.43-3
ii  libcap-ng0   0.9.3-1+b1
ii  libgcc-s1    16.2.0-1
ii  libseccomp2  2.6.1-1
ii  uidmap       1:4.19.3-2

virtiofsd recommends no packages.

virtiofsd suggests no packages.

-- no debconf information

-- 
Simon John