From: Fiona Ebner <f.ebner@proxmox.com>
Date: Tue, 10 Mar 2026 14:25:39 +0000 (+0100)
Subject: ui/vdagent: add migration blocker when machine version < 10.1
X-Git-Tag: v11.0.0-rc0~4^2~13
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6f23dde620efa2de1cf3c56dfb474a20d9ce876d;p=thirdparty%2Fqemu.git

ui/vdagent: add migration blocker when machine version < 10.1

In QEMU 10.1, commit 5d56bff11e ("ui/vdagent: add migration support")
added migration support for the vdagent chardev and commit 42000e0013
("ui/vdagent: remove migration blocker") removed the migration
blocker. No compat for older machine versions was added, so migration
with pre-10.1 machine version, from a 10.1 binary to a pre-10.1 binary
will result in a failure when loading the VM state in the target
instance:

> Unknown savevm section or instance 'vdagent' 0. Make sure that your
> current VM setup matches your saved VM setup, including any
> hotplugged devices

Add a compat flag to block migration when the machine version is less
than 10.1 to avoid this.

Cc: qemu-stable@nongnu.org
Fixes: 42000e0013 ("ui/vdagent: remove migration blocker")
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20260310142552.240877-1-f.ebner@proxmox.com>
---

diff --git a/hw/core/machine.c b/hw/core/machine.c
index a14ad05b9a6..6cf0e2f404e 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -57,6 +57,7 @@ GlobalProperty hw_compat_10_0[] = {
     { "vfio-pci", "x-migration-load-config-after-iter", "off" },
     { "ramfb", "use-legacy-x86-rom", "true"},
     { "vfio-pci-nohotplug", "use-legacy-x86-rom", "true" },
+    { "chardev-qemu-vdagent", "x-migration-blocked", "true" },
 };
 const size_t hw_compat_10_0_len = G_N_ELEMENTS(hw_compat_10_0);
 
diff --git a/ui/vdagent.c b/ui/vdagent.c
index 5a5e4bf6818..bb0c4aa14ca 100644
--- a/ui/vdagent.c
+++ b/ui/vdagent.c
@@ -6,6 +6,8 @@
 #include "qemu/option.h"
 #include "qemu/units.h"
 #include "hw/core/qdev.h"
+#include "hw/core/qdev-properties.h"
+#include "migration/blocker.h"
 #include "ui/clipboard.h"
 #include "ui/console.h"
 #include "ui/input.h"
@@ -24,6 +26,10 @@
 struct VDAgentChardev {
     Chardev parent;
 
+    /* needed for machine versions < 10.1 when migration was not supported */
+    Error *migration_blocker;
+    bool migration_blocked;
+
     /* config */
     bool mouse;
     bool clipboard;
@@ -657,6 +663,12 @@ static bool vdagent_chr_open(Chardev *chr, ChardevBackend *backend,
     return false;
 #endif
 
+    if (vd->migration_blocked) {
+        if (migrate_add_blocker(&vd->migration_blocker, errp) != 0) {
+            return false;
+        }
+    }
+
     vd->mouse = VDAGENT_MOUSE_DEFAULT;
     if (cfg->has_mouse) {
         vd->mouse = cfg->mouse;
@@ -901,6 +913,19 @@ static void vdagent_chr_parse(QemuOpts *opts, ChardevBackend *backend,
 
 /* ------------------------------------------------------------------ */
 
+static bool get_migration_blocked(Object *o, Error **errp)
+{
+    VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(o);
+    return vd->migration_blocked;
+}
+
+static void set_migration_blocked(Object *o, bool migration_blocked,
+                                   Error **errp)
+{
+    VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(o);
+    vd->migration_blocked = migration_blocked;
+}
+
 static void vdagent_chr_class_init(ObjectClass *oc, const void *data)
 {
     ChardevClass *cc = CHARDEV_CLASS(oc);
@@ -910,6 +935,10 @@ static void vdagent_chr_class_init(ObjectClass *oc, const void *data)
     cc->chr_write        = vdagent_chr_write;
     cc->chr_set_fe_open  = vdagent_chr_set_fe_open;
     cc->chr_accept_input = vdagent_chr_accept_input;
+
+    object_class_property_add_bool(oc, "x-migration-blocked",
+                                   get_migration_blocked,
+                                   set_migration_blocked);
 }
 
 static int post_load(void *opaque, int version_id)
@@ -1064,10 +1093,26 @@ static void vdagent_chr_instance_init(Object *obj)
     vmstate_register_any(NULL, &vmstate_vdagent, vd);
 }
 
+static void vdagent_post_init(Object *obj)
+{
+    VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(obj);
+
+    object_apply_compat_props(obj);
+
+    if (vd->migration_blocked) {
+        error_setg(&vd->migration_blocker,
+                   "The vdagent chardev doesn't support migration with machine"
+                   " version less than 10.1");
+    }
+}
+
 static void vdagent_chr_fini(Object *obj)
 {
     VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(obj);
 
+    if (vd->migration_blocked) {
+        migrate_del_blocker(&vd->migration_blocker);
+    }
     vdagent_disconnect(vd);
     if (vd->mouse_hs) {
         qemu_input_handler_unregister(vd->mouse_hs);
@@ -1080,6 +1125,7 @@ static const TypeInfo vdagent_chr_type_info = {
     .parent = TYPE_CHARDEV,
     .instance_size = sizeof(VDAgentChardev),
     .instance_init = vdagent_chr_instance_init,
+    .instance_post_init = vdagent_post_init,
     .instance_finalize = vdagent_chr_fini,
     .class_init = vdagent_chr_class_init,
 };