iothread: add "iothread" qdev property type

Add a "iothread" qdev property type so devices can be hooked up to an
IOThread from the comand-line:

  qemu -object iothread,id=iothread0 \
       -device some-device,x-iothread=iothread0

Note that Paolo Bonzini <pbonzini@redhat.com> has suggested using QOM
links instead.  This way the relationship between the objects is
reflected in QOM.  There are currently shortcomings of
object_property_add_link() which prevent this use case.  I will attempt
to fix them and move to QOM links in a separate series.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/core/qdev-properties-system.c

@@ -18,6 +18,7 @@
 #include "net/hub.h"
 #include "qapi/visitor.h"
 #include "sysemu/char.h"
+#include "sysemu/iothread.h"
 
 static void get_pointer(Object *obj, Visitor *v, Property *prop,
                         char *(*print)(void *ptr),
@@ -385,6 +386,56 @@ void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd)
     nd->instantiated = 1;
 }
 
+/* --- iothread --- */
+
+static char *print_iothread(void *ptr)
+{
+    return iothread_get_id(ptr);
+}
+
+static int parse_iothread(DeviceState *dev, const char *str, void **ptr)
+{
+    IOThread *iothread;
+
+    iothread = iothread_find(str);
+    if (!iothread) {
+        return -ENOENT;
+    }
+    object_ref(OBJECT(iothread));
+    *ptr = iothread;
+    return 0;
+}
+
+static void get_iothread(Object *obj, struct Visitor *v, void *opaque,
+                         const char *name, Error **errp)
+{
+    get_pointer(obj, v, opaque, print_iothread, name, errp);
+}
+
+static void set_iothread(Object *obj, struct Visitor *v, void *opaque,
+                         const char *name, Error **errp)
+{
+    set_pointer(obj, v, opaque, parse_iothread, name, errp);
+}
+
+static void release_iothread(Object *obj, const char *name, void *opaque)
+{
+    DeviceState *dev = DEVICE(obj);
+    Property *prop = opaque;
+    IOThread **ptr = qdev_get_prop_ptr(dev, prop);
+
+    if (*ptr) {
+        object_unref(OBJECT(*ptr));
+    }
+}
+
+PropertyInfo qdev_prop_iothread = {
+    .name = "iothread",
+    .get = get_iothread,
+    .set = set_iothread,
+    .release = release_iothread,
+};
+
 static int qdev_add_one_global(QemuOpts *opts, void *opaque)
 {
     GlobalProperty *g;

include/hw/qdev-properties.h

@@ -22,6 +22,7 @@ extern PropertyInfo qdev_prop_bios_chs_trans;
 extern PropertyInfo qdev_prop_drive;
 extern PropertyInfo qdev_prop_netdev;
 extern PropertyInfo qdev_prop_vlan;
+extern PropertyInfo qdev_prop_iothread;
 extern PropertyInfo qdev_prop_pci_devfn;
 extern PropertyInfo qdev_prop_blocksize;
 extern PropertyInfo qdev_prop_pci_host_devaddr;
@@ -142,6 +143,8 @@ extern PropertyInfo qdev_prop_arraylen;
     DEFINE_PROP(_n, _s, _f, qdev_prop_vlan, NICPeers)
 #define DEFINE_PROP_DRIVE(_n, _s, _f) \
     DEFINE_PROP(_n, _s, _f, qdev_prop_drive, BlockDriverState *)
+#define DEFINE_PROP_IOTHREAD(_n, _s, _f)             \
+    DEFINE_PROP(_n, _s, _f, qdev_prop_iothread, IOThread *)
 #define DEFINE_PROP_MACADDR(_n, _s, _f)         \
     DEFINE_PROP(_n, _s, _f, qdev_prop_macaddr, MACAddr)
 #define DEFINE_PROP_LOSTTICKPOLICY(_n, _s, _f, _d) \