[PATCH 09/12] hw/xen: prevent duplicate device registrations

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

Ensure that we have a XenBackendInstance for every device regardless
of whether it was "discovered" in XenStore or created directly in QEMU.

This allows the backend_list to be a source of truth about whether a
given backend exists, and allows us to reject duplicates.

This also cleans up the fact that backend drivers were calling
xen_backend_set_device() with a XenDevice immediately after calling
qdev_realize_and_unref() on it, when it wasn't theirs to play with any
more.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/block/xen-block.c         |  1 -
 hw/char/xen_console.c        |  2 +-
 hw/xen/xen-backend.c         | 78 ++++++++++++++++++++++++++----------
 hw/xen/xen-bus.c             |  8 ++++
 include/hw/xen/xen-backend.h |  3 ++
 5 files changed, 69 insertions(+), 23 deletions(-)

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index a07cd7eb5d..9262338535 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -975,7 +975,6 @@ static void xen_block_device_create(XenBackendInstance *backend,
         goto fail;
     }
 
-    xen_backend_set_device(backend, xendev);
     return;
 
 fail:
diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index bd20be116c..2825b8c511 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -468,7 +468,7 @@ static void xen_console_device_create(XenBackendInstance *backend,
     Chardev *cd = NULL;
     struct qemu_xs_handle *xsh = xenbus->xsh;
 
-    if (qemu_strtoul(name, NULL, 10, &number)) {
+    if (qemu_strtoul(name, NULL, 10, &number) || number >= INT_MAX) {
         error_setg(errp, "failed to parse name '%s'", name);
         goto fail;
     }
diff --git a/hw/xen/xen-backend.c b/hw/xen/xen-backend.c
index b9bf70a9f5..dcb4329258 100644
--- a/hw/xen/xen-backend.c
+++ b/hw/xen/xen-backend.c
@@ -101,22 +101,28 @@ static XenBackendInstance *xen_backend_list_find(XenDevice *xendev)
     return NULL;
 }
 
-bool xen_backend_exists(const char *type, const char *name)
+static XenBackendInstance *xen_backend_lookup(const XenBackendImpl *impl, const char *name)
 {
-    const XenBackendImpl *impl = xen_backend_table_lookup(type);
     XenBackendInstance *backend;
 
-    if (!impl) {
-        return false;
-    }
-
     QLIST_FOREACH(backend, &backend_list, entry) {
         if (backend->impl == impl && !strcmp(backend->name, name)) {
-            return true;
+            return backend;
         }
     }
 
-    return false;
+    return NULL;
+}
+
+bool xen_backend_exists(const char *type, const char *name)
+{
+    const XenBackendImpl *impl = xen_backend_table_lookup(type);
+
+    if (!impl) {
+        return false;
+    }
+
+    return !!xen_backend_lookup(impl, name);
 }
 
 static void xen_backend_list_remove(XenBackendInstance *backend)
@@ -138,11 +144,10 @@ void xen_backend_device_create(XenBus *xenbus, const char *type,
     backend = g_new0(XenBackendInstance, 1);
     backend->xenbus = xenbus;
     backend->name = g_strdup(name);
-
-    impl->create(backend, opts, errp);
-
     backend->impl = impl;
     xen_backend_list_add(backend);
+
+    impl->create(backend, opts, errp);
 }
 
 XenBus *xen_backend_get_bus(XenBackendInstance *backend)
@@ -155,13 +160,6 @@ const char *xen_backend_get_name(XenBackendInstance *backend)
     return backend->name;
 }
 
-void xen_backend_set_device(XenBackendInstance *backend,
-                            XenDevice *xendev)
-{
-    g_assert(!backend->xendev);
-    backend->xendev = xendev;
-}
-
 XenDevice *xen_backend_get_device(XenBackendInstance *backend)
 {
     return backend->xendev;
@@ -178,9 +176,7 @@ bool xen_backend_try_device_destroy(XenDevice *xendev, Error **errp)
     }
 
     impl = backend->impl;
-    if (backend->xendev) {
-        impl->destroy(backend, errp);
-    }
+    impl->destroy(backend, errp);
 
     xen_backend_list_remove(backend);
     g_free(backend->name);
@@ -188,3 +184,43 @@ bool xen_backend_try_device_destroy(XenDevice *xendev, Error **errp)
 
     return true;
 }
+
+bool xen_backend_device_realized(XenDevice *xendev, Error **errp)
+{
+    XenDeviceClass *xendev_class = XEN_DEVICE_GET_CLASS(xendev);
+    const char *type = xendev_class->backend ? : object_get_typename(OBJECT(xendev));
+    const XenBackendImpl *impl = xen_backend_table_lookup(type);
+    XenBackendInstance *backend;
+
+    if (!impl) {
+        return false;
+    }
+
+    backend = xen_backend_lookup(impl, xendev->name);
+    if (backend) {
+        if (backend->xendev && backend->xendev != xendev) {
+            error_setg(errp, "device %s/%s already exists", type, xendev->name);
+            return false;
+        }
+        backend->xendev = xendev;
+        return true;
+    }
+
+    backend = g_new0(XenBackendInstance, 1);
+    backend->xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
+    backend->xendev = xendev;
+    backend->name = g_strdup(xendev->name);
+    backend->impl = impl;
+
+    xen_backend_list_add(backend);
+    return true;
+}
+
+void xen_backend_device_unrealized(XenDevice *xendev)
+{
+    XenBackendInstance *backend = xen_backend_list_find(xendev);
+
+    if (backend) {
+        backend->xendev = NULL;
+    }
+}
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 0da2aa219a..0b232d1f94 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -359,6 +359,8 @@ static void xen_bus_realize(BusState *bus, Error **errp)
 
     g_free(type);
     g_free(key);
+
+    xen_bus_enumerate(xenbus);
     return;
 
 fail:
@@ -958,6 +960,8 @@ static void xen_device_unrealize(DeviceState *dev)
 
     trace_xen_device_unrealize(type, xendev->name);
 
+    xen_backend_device_unrealized(xendev);
+
     if (xendev->exit.notify) {
         qemu_remove_exit_notifier(&xendev->exit);
         xendev->exit.notify = NULL;
@@ -1024,6 +1028,10 @@ static void xen_device_realize(DeviceState *dev, Error **errp)
         goto unrealize;
     }
 
+    if (!xen_backend_device_realized(xendev, errp)) {
+        goto unrealize;
+    }
+
     trace_xen_device_realize(type, xendev->name);
 
     xendev->xsh = qemu_xen_xs_open();
diff --git a/include/hw/xen/xen-backend.h b/include/hw/xen/xen-backend.h
index 0f01631ae7..3f1e764c51 100644
--- a/include/hw/xen/xen-backend.h
+++ b/include/hw/xen/xen-backend.h
@@ -38,4 +38,7 @@ void xen_backend_device_create(XenBus *xenbus, const char *type,
                                const char *name, QDict *opts, Error **errp);
 bool xen_backend_try_device_destroy(XenDevice *xendev, Error **errp);
 
+bool xen_backend_device_realized(XenDevice *xendev, Error **errp);
+void xen_backend_device_unrealized(XenDevice *xendev);
+
 #endif /* HW_XEN_BACKEND_H */
-- 
2.40.1