hw/xen: Implement core serialize/deserialize methods for xenstore_impl

This implements the basic migration support in the back end, with unit
tests that give additional confidence in the node-counting already in
the tree.

However, the existing PV back ends like xen-disk don't support migration
yet. They will reset the ring and fail to continue where they left off.
We will fix that in future, but not in time for the 8.0 release.

Since there's also an open question of whether we want to serialize the
full XenStore or only the guest-owned nodes in /local/domain/${domid},
for now just mark the XenStore device as unmigratable.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 25 insertions, 1 deletions

diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index 3b409e3817..520422b147 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -66,6 +66,9 @@ struct XenXenstoreState {
     evtchn_port_t guest_port;
     evtchn_port_t be_port;
     struct xenevtchn_handle *eh;
+
+    uint8_t *impl_state;
+    uint32_t impl_state_size;
 };
 
 struct XenXenstoreState *xen_xenstore_singleton;
@@ -109,16 +112,26 @@ static bool xen_xenstore_is_needed(void *opaque)
 static int xen_xenstore_pre_save(void *opaque)
 {
     XenXenstoreState *s = opaque;
+    GByteArray *save;
 
     if (s->eh) {
         s->guest_port = xen_be_evtchn_get_guest_port(s->eh);
     }
+
+    g_free(s->impl_state);
+    save = xs_impl_serialize(s->impl);
+    s->impl_state = save->data;
+    s->impl_state_size = save->len;
+    g_byte_array_free(save, false);
+
     return 0;
 }
 
 static int xen_xenstore_post_load(void *opaque, int ver)
 {
     XenXenstoreState *s = opaque;
+    GByteArray *save;
+    int ret;
 
     /*
      * As qemu/dom0, rebind to the guest's port. The Windows drivers may
@@ -135,11 +148,18 @@ static int xen_xenstore_post_load(void *opaque, int ver)
         }
         s->be_port = be_port;
     }
-    return 0;
+
+    save = g_byte_array_new_take(s->impl_state, s->impl_state_size);
+    s->impl_state = NULL;
+    s->impl_state_size = 0;
+
+    ret = xs_impl_deserialize(s->impl, save, xen_domid, fire_watch_cb, s);
+    return ret;
 }
 
 static const VMStateDescription xen_xenstore_vmstate = {
     .name = "xen_xenstore",
+    .unmigratable = 1, /* The PV back ends don't migrate yet */
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = xen_xenstore_is_needed,
@@ -155,6 +175,10 @@ static const VMStateDescription xen_xenstore_vmstate = {
         VMSTATE_BOOL(rsp_pending, XenXenstoreState),
         VMSTATE_UINT32(guest_port, XenXenstoreState),
         VMSTATE_BOOL(fatal_error, XenXenstoreState),
+        VMSTATE_UINT32(impl_state_size, XenXenstoreState),
+        VMSTATE_VARRAY_UINT32_ALLOC(impl_state, XenXenstoreState,
+                                    impl_state_size, 0,
+                                    vmstate_info_uint8, uint8_t),
         VMSTATE_END_OF_LIST()
     }
 };