[From nobody Thu Aug 13 21:53:09 2026
Received: (at submit) by bugs.debian.org; 11 Aug 2026 10:34:50 +0000
X-Spam-Checker-Version: SpamAssassin 4.0.1-bugs.debian.org_2005_01_02
 (2024-03-25) on buxtehude.debian.org
X-Spam-Level: 
X-Spam-Status: No, score=-14.1 required=4.0 tests=BAYES_00,
 BODY_INCLUDES_PACKAGE,FOURLA,HAS_PACKAGE,RDNS_NONE,SPF_HELO_NONE,
 SPF_PASS autolearn=ham autolearn_force=no
 version=4.0.1-bugs.debian.org_2005_01_02
X-Spam-Bayes: score:0.0000 Tokens: new, 74; hammy, 150; neutral, 168; spammy,
 0. spammytokens: hammytokens:0.000-+--trixie, 0.000-+--python3, 
 0.000-+--H*Ad:N*Bug, 0.000-+--HTo:N*Debian, 0.000-+--forky
Return-path: <debian3@the-jedi.co.uk>
Received: from [2a00:1098:82:67::1] (port=49014 helo=vps.the-jedi.co.uk)
 by buxtehude.debian.org with esmtps
 (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256)
 (Exim 4.96) (envelope-from <debian3@the-jedi.co.uk>)
 id 1wtjoo-00AbVm-1q for submit@bugs.debian.org;
 Tue, 11 Aug 2026 10:34:50 +0000
Received: from [IPV6:2a02:8012:74f5:0:f56:4cb2:2605:c45c] (unknown
 [IPv6:2a02:8012:74f5:0:f56:4cb2:2605:c45c])
 by vps.the-jedi.co.uk (Postfix) with ESMTPSA id 2B1E14240F
 for <submit@bugs.debian.org>; Tue, 11 Aug 2026 11:28:51 +0100 (BST)
Message-ID: <76a916ee-374f-4df4-b83c-edd1f9b32350@the-jedi.co.uk>
Date: Tue, 11 Aug 2026 11:28:50 +0100
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: virtiofsd: Fails to mount with "vhost_backend_init failed: Protocol
 error"
Content-Language: en-US
From: Simon John <debian3@the-jedi.co.uk>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Greylist: delayed 353 seconds by postgrey-1.37 at buxtehude;
 Tue, 11 Aug 2026 10:34:50 UTC
Delivered-To: submit@bugs.debian.org

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
]