[Qemu-devel] [PATCH v2 2/3] migration: Allow to suppress vmdesc submission

[Alexander Graf <agraf@suse.de>]

We now always send a JSON blob describing the migration file format as part
of the migration stream. However, some tools built around QEMU have proven
to stumble over this.

This patch gives the user the chance to disable said self-describing part of
the migration stream. To disable vmdesc submission, just add

  -machine suppress-vmdesc=on

to your QEMU command line.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 hw/core/machine.c   | 20 ++++++++++++++++++++
 include/hw/boards.h |  1 +
 qemu-options.hx     |  3 ++-
 savevm.c            | 14 +++++++++++---
 4 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index fbd91be..53409b2 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -260,6 +260,20 @@ static void machine_set_iommu(Object *obj, bool value, Error **errp)
     ms->iommu = value;
 }
 
+static void machine_set_suppress_vmdesc(Object *obj, bool value, Error **errp)
+{
+    MachineState *ms = MACHINE(obj);
+
+    ms->suppress_vmdesc = value;
+}
+
+static bool machine_get_suppress_vmdesc(Object *obj, Error **errp)
+{
+    MachineState *ms = MACHINE(obj);
+
+    return ms->suppress_vmdesc;
+}
+
 static int error_on_sysbus_device(SysBusDevice *sbdev, void *opaque)
 {
     error_report("Option '-device %s' cannot be handled by this machine",
@@ -378,6 +392,12 @@ static void machine_initfn(Object *obj)
     object_property_set_description(obj, "iommu",
                                     "Set on/off to enable/disable Intel IOMMU (VT-d)",
                                     NULL);
+    object_property_add_bool(obj, "suppress-vmdesc",
+                             machine_get_suppress_vmdesc,
+                             machine_set_suppress_vmdesc, NULL);
+    object_property_set_description(obj, "suppress-vmdesc",
+                                    "Set on to disable self-describing migration",
+                                    NULL);
 
     /* Register notifier when init is done for sysbus sanity checks */
     ms->sysbus_notifier.notify = machine_init_notify;
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 3ddc449..bf87a29 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -135,6 +135,7 @@ struct MachineState {
     bool usb;
     char *firmware;
     bool iommu;
+    bool suppress_vmdesc;
 
     ram_addr_t ram_size;
     ram_addr_t maxram_size;
diff --git a/qemu-options.hx b/qemu-options.hx
index 85ca3ad..86be4f4 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
     "                kvm_shadow_mem=size of KVM shadow MMU\n"
     "                dump-guest-core=on|off include guest memory in a core dump (default=on)\n"
     "                mem-merge=on|off controls memory merge support (default: on)\n"
-    "                iommu=on|off controls emulated Intel IOMMU (VT-d) support (default=off)\n",
+    "                iommu=on|off controls emulated Intel IOMMU (VT-d) support (default=off)\n"
+    "                suppress-vmdesc=on|off disables self-describing migration (default=off)\n",
     QEMU_ARCH_ALL)
 STEXI
 @item -machine [type=]@var{name}[,prop=@var{value}[,...]]
diff --git a/savevm.c b/savevm.c
index 1b78654..8a0ecf2 100644
--- a/savevm.c
+++ b/savevm.c
@@ -710,6 +710,12 @@ int qemu_savevm_state_iterate(QEMUFile *f)
     return ret;
 }
 
+static bool should_send_vmdesc(void)
+{
+    MachineState *machine = MACHINE(qdev_get_machine());
+    return !machine->suppress_vmdesc;
+}
+
 void qemu_savevm_state_complete(QEMUFile *f)
 {
     QJSON *vmdesc;
@@ -782,9 +788,11 @@ void qemu_savevm_state_complete(QEMUFile *f)
     qjson_finish(vmdesc);
     vmdesc_len = strlen(qjson_get_str(vmdesc));
 
-    qemu_put_byte(f, QEMU_VM_VMDESCRIPTION);
-    qemu_put_be32(f, vmdesc_len);
-    qemu_put_buffer(f, (uint8_t *)qjson_get_str(vmdesc), vmdesc_len);
+    if (should_send_vmdesc()) {
+        qemu_put_byte(f, QEMU_VM_VMDESCRIPTION);
+        qemu_put_be32(f, vmdesc_len);
+        qemu_put_buffer(f, (uint8_t *)qjson_get_str(vmdesc), vmdesc_len);
+    }
     object_unref(OBJECT(vmdesc));
 
     qemu_fflush(f);
-- 
1.7.12.4