From: Ján Tomko <jtomko@redhat.com>

In that case, libvirtd cannot set it on the command line because
virtiofsd is not launched by libvirt.

https://issues.redhat.com/browse/RHEL-87522

Signed-off-by: Ján Tomko <jtomko@redhat.com>
---
 src/qemu/qemu_validate.c                      |  6 +++
 ...st-user-fs-sock-readonly.x86_64-latest.err |  1 +
 .../vhost-user-fs-sock-readonly.xml           | 41 +++++++++++++++++++
 tests/qemuxmlconftest.c                       |  1 +
 4 files changed, 49 insertions(+)
 create mode 100644 tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.x86_64-latest.err
 create mode 100644 tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.xml

diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index 3e8fdb2268..3b0f2b50a5 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -5022,6 +5022,12 @@ qemuValidateDomainDeviceDefFS(virDomainFSDef *fs,
                                _("virtiofs does not support wrpolicy"));
                 return -1;
             }
+        } else {
+            if (fs->readonly) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("readonly mode cannot be set for externally started virtiofsd"));
+                return -1;
+            }
         }
 
         if (fs->model != VIR_DOMAIN_FS_MODEL_DEFAULT) {
diff --git a/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.x86_64-latest.err b/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.x86_64-latest.err
new file mode 100644
index 0000000000..d6df9bddb8
--- /dev/null
+++ b/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.x86_64-latest.err
@@ -0,0 +1 @@
+unsupported configuration: readonly mode cannot be set for externally started virtiofsd
diff --git a/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.xml b/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.xml
new file mode 100644
index 0000000000..39e27ccfba
--- /dev/null
+++ b/tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.xml
@@ -0,0 +1,41 @@
+<domain type='kvm'>
+  <name>guest</name>
+  <uuid>126f2720-6f8e-45ab-a886-ec9277079a67</uuid>
+  <memory unit='KiB'>14680064</memory>
+  <currentMemory unit='KiB'>14680064</currentMemory>
+  <memoryBacking>
+    <source type='file'/>
+    <access mode='shared'/>
+  </memoryBacking>
+  <vcpu placement='static'>2</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <cpu mode='custom' match='exact' check='none'>
+    <model fallback='forbid'>qemu64</model>
+    <numa>
+      <cell id='0' cpus='0-1' memory='14680064' unit='KiB' memAccess='shared'/>
+    </numa>
+  </cpu>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='usb' index='0' model='none'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <filesystem type='mount'>
+      <driver type='virtiofs' queue='1024'/>
+      <source socket='/tmp/sock'/>
+      <target dir='tag'/>
+      <readonly/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+    </filesystem>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <audio id='1' type='none'/>
+    <memballoon model='none'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxmlconftest.c b/tests/qemuxmlconftest.c
index e4d80faa99..1f39779d7b 100644
--- a/tests/qemuxmlconftest.c
+++ b/tests/qemuxmlconftest.c
@@ -3259,6 +3259,7 @@ mymain(void)
     DO_TEST_CAPS_LATEST("seclabel-dynamic-none");
     DO_TEST_CAPS_LATEST("serial-target-port-auto");
     DO_TEST_CAPS_LATEST("vhost-user-fs-sock");
+    DO_TEST_CAPS_LATEST_PARSE_ERROR("vhost-user-fs-sock-readonly");
     DO_TEST_CAPS_ARCH_LATEST("video-virtio-gpu-ccw-auto", "s390x");
 
     DO_TEST_CAPS_LATEST("graphics-listen-network");
-- 
2.50.1

On 10/21/25 15:10, Ján Tomko via Devel wrote:
> From: Ján Tomko <jtomko@redhat.com>
> 
> In that case, libvirtd cannot set it on the command line because
> virtiofsd is not launched by libvirt.
> 
> https://issues.redhat.com/browse/RHEL-87522
> 
> Signed-off-by: Ján Tomko <jtomko@redhat.com>
> ---
>  src/qemu/qemu_validate.c                      |  6 +++
>  ...st-user-fs-sock-readonly.x86_64-latest.err |  1 +
>  .../vhost-user-fs-sock-readonly.xml           | 41 +++++++++++++++++++
>  tests/qemuxmlconftest.c                       |  1 +
>  4 files changed, 49 insertions(+)
>  create mode 100644 tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.x86_64-latest.err
>  create mode 100644 tests/qemuxmlconfdata/vhost-user-fs-sock-readonly.xml
> 
> diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
> index 3e8fdb2268..3b0f2b50a5 100644
> --- a/src/qemu/qemu_validate.c
> +++ b/src/qemu/qemu_validate.c
> @@ -5022,6 +5022,12 @@ qemuValidateDomainDeviceDefFS(virDomainFSDef *fs,
>                                 _("virtiofs does not support wrpolicy"));
>                  return -1;
>              }
> +        } else {
> +            if (fs->readonly) {
> +                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                               _("readonly mode cannot be set for externally started virtiofsd"));
> +                return -1;
> +            }

I think there's more to be checked (e.g. fs->cache, fs->sandbox,
fs->xattr, etc.), but this is a good start.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal