qom: add support for qom objects in modules.

build some devices (qxl, virtio-gpu, ccid, usb-redir) as modules.
 build braille chardev as module.
 
 v2: more verbose comment for "build: fix device module builds" patch.
 
 note: qemu doesn't rebuild objects on cflags changes (specifically
       -fPIC being added when code is switched from builtin to module).
       Workaround for resulting build errors: "make clean", rebuild.
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Merge remote-tracking branch 'remotes/kraxel/tags/modules-20200707-pull-request' into staging

qom: add support for qom objects in modules.
build some devices (qxl, virtio-gpu, ccid, usb-redir) as modules.
build braille chardev as module.

v2: more verbose comment for "build: fix device module builds" patch.

note: qemu doesn't rebuild objects on cflags changes (specifically
      -fPIC being added when code is switched from builtin to module).
      Workaround for resulting build errors: "make clean", rebuild.

# gpg: Signature made Tue 07 Jul 2020 14:42:16 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/modules-20200707-pull-request:
  chardev: enable modules, use for braille
  vga: build virtio-gpu as module
  vga: build virtio-gpu only once
  vga: build qxl as module
  usb: build usb-redir as module
  ccid: build smartcard as module
  build: fix device module builds
  qdev: device module support
  object: qom module support
  module: qom module support

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Makefile.objs

@@ -59,6 +59,7 @@ common-obj-y += migration/
 common-obj-y += audio/
 common-obj-m += audio/
 common-obj-y += hw/
+common-obj-m += hw/
 
 common-obj-y += replay/
 
@@ -70,6 +71,7 @@ common-obj-$(CONFIG_TPM) += tpm.o
 
 common-obj-y += backends/
 common-obj-y += chardev/
+common-obj-m += chardev/
 
 common-obj-$(CONFIG_SECCOMP) += qemu-seccomp.o
 qemu-seccomp.o-cflags := $(SECCOMP_CFLAGS)

Makefile.target

@@ -179,6 +179,20 @@ endif # CONFIG_SOFTMMU
 dummy := $(call unnest-vars,,obj-y)
 all-obj-y := $(obj-y)
 
+#
+# common-obj-m has some crap here, probably as side effect from
+# unnest-vars recursing into target directories to fill obj-y and not
+# properly handling the -m case.
+#
+# Clear common-obj-m as workaround.  Fixes suspious dependency errors
+# when building devices as modules.  A bit hackish, but should be ok
+# as long as we do not have any target-specific modules.
+#
+# The meson-based build system currently in development doesn't need
+# unnest-vars and will obsolete this workaround.
+#
+common-obj-m :=
+
 include $(SRC_PATH)/Makefile.objs
 dummy := $(call unnest-vars,.., \
                authz-obj-y \

chardev/Makefile.objs

@@ -18,8 +18,11 @@ chardev-obj-$(CONFIG_WIN32) += char-win.o
 chardev-obj-$(CONFIG_WIN32) += char-win-stdio.o
 
 common-obj-y += msmouse.o wctablet.o testdev.o
-common-obj-$(CONFIG_BRLAPI) += baum.o
+
+ifeq ($(CONFIG_BRLAPI),y)
+common-obj-m += baum.o
 baum.o-cflags := $(SDL_CFLAGS)
 baum.o-libs := $(BRLAPI_LIBS)
+endif
 
 common-obj-$(CONFIG_SPICE) += spice.o

chardev/char.c

@@ -527,7 +527,7 @@ static const ChardevClass *char_get_class(const char *driver, Error **errp)
     const ChardevClass *cc;
     char *typename = g_strdup_printf("chardev-%s", driver);
 
-    oc = object_class_by_name(typename);
+    oc = module_object_class_by_name(typename);
     g_free(typename);
 
     if (!object_class_dynamic_cast(oc, TYPE_CHARDEV)) {

hw/Makefile.objs

@@ -43,4 +43,6 @@ devices-dirs-y += smbios/
 endif
 
 common-obj-y += $(devices-dirs-y)
+common-obj-m += display/
+common-obj-m += usb/
 obj-y += $(devices-dirs-y)

hw/core/qdev.c

@@ -137,6 +137,9 @@ void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
  */
 DeviceState *qdev_new(const char *name)
 {
+    if (!object_class_by_name(name)) {
+        module_load_qom_one(name);
+    }
     return DEVICE(object_new(name));
 }
 
@@ -147,10 +150,9 @@ DeviceState *qdev_new(const char *name)
  */
 DeviceState *qdev_try_new(const char *name)
 {
-    if (!object_class_by_name(name)) {
+    if (!module_object_class_by_name(name)) {
         return NULL;
     }
-
     return DEVICE(object_new(name));
 }
 

hw/display/Makefile.objs

@@ -44,18 +44,24 @@ common-obj-$(CONFIG_ARTIST) += artist.o
 
 obj-$(CONFIG_VGA) += vga.o
 
-common-obj-$(CONFIG_QXL) += qxl.o qxl-logger.o qxl-render.o
+ifeq ($(CONFIG_QXL),y)
+common-obj-m += qxl.mo
+qxl.mo-objs = qxl.o qxl-logger.o qxl-render.o
+endif
+
+ifeq ($(CONFIG_VIRTIO_GPU),y)
+common-obj-m += virtio-gpu.mo
+virtio-gpu-obj-$(CONFIG_VIRTIO_GPU) += virtio-gpu-base.o virtio-gpu.o virtio-gpu-3d.o
+virtio-gpu-obj-$(CONFIG_VHOST_USER_GPU) += vhost-user-gpu.o
+virtio-gpu-obj-$(call land,$(CONFIG_VIRTIO_GPU),$(CONFIG_VIRTIO_PCI)) += virtio-gpu-pci.o
+virtio-gpu-obj-$(call land,$(CONFIG_VHOST_USER_GPU),$(CONFIG_VIRTIO_PCI)) += vhost-user-gpu-pci.o
+virtio-gpu-obj-$(CONFIG_VIRTIO_VGA) += virtio-vga.o
+virtio-gpu-obj-$(CONFIG_VHOST_USER_VGA) += vhost-user-vga.o
+virtio-gpu.mo-objs := $(virtio-gpu-obj-y)
+virtio-gpu.mo-cflags := $(VIRGL_CFLAGS)
+virtio-gpu.mo-libs := $(VIRGL_LIBS)
+endif
 
-obj-$(CONFIG_VIRTIO_GPU) += virtio-gpu-base.o virtio-gpu.o virtio-gpu-3d.o
-obj-$(CONFIG_VHOST_USER_GPU) += vhost-user-gpu.o
-obj-$(call land,$(CONFIG_VIRTIO_GPU),$(CONFIG_VIRTIO_PCI)) += virtio-gpu-pci.o
-obj-$(call land,$(CONFIG_VHOST_USER_GPU),$(CONFIG_VIRTIO_PCI)) += vhost-user-gpu-pci.o
-obj-$(CONFIG_VIRTIO_VGA) += virtio-vga.o
-obj-$(CONFIG_VHOST_USER_VGA) += vhost-user-vga.o
-virtio-gpu.o-cflags := $(VIRGL_CFLAGS)
-virtio-gpu.o-libs += $(VIRGL_LIBS)
-virtio-gpu-3d.o-cflags := $(VIRGL_CFLAGS)
-virtio-gpu-3d.o-libs += $(VIRGL_LIBS)
 common-obj-$(CONFIG_DPCD) += dpcd.o
 common-obj-$(CONFIG_XLNX_ZYNQMP_ARM) += xlnx_dp.o
 

hw/usb/Makefile.objs

@@ -29,11 +29,13 @@ common-obj-$(CONFIG_USB_NETWORK)      += dev-network.o
 
 ifeq ($(CONFIG_USB_SMARTCARD),y)
 common-obj-y                          += dev-smartcard-reader.o
-common-obj-$(CONFIG_SMARTCARD)        += smartcard.mo
+ifeq ($(CONFIG_SMARTCARD),y)
+common-obj-m                          += smartcard.mo
 smartcard.mo-objs := ccid-card-passthru.o ccid-card-emulated.o
 smartcard.mo-cflags := $(SMARTCARD_CFLAGS)
 smartcard.mo-libs := $(SMARTCARD_LIBS)
 endif
+endif
 
 ifeq ($(CONFIG_POSIX),y)
 common-obj-$(CONFIG_USB_STORAGE_MTP)  += dev-mtp.o
@@ -41,9 +43,12 @@ endif
 
 # usb redirection
 ifeq ($(CONFIG_USB),y)
-common-obj-$(CONFIG_USB_REDIR) += redirect.o quirks.o
+ifeq ($(CONFIG_USB_REDIR),y)
-redirect.o-cflags = $(USB_REDIR_CFLAGS)
+common-obj-m += redirect.mo
-redirect.o-libs = $(USB_REDIR_LIBS)
+redirect.mo-objs = redirect.o quirks.o
+redirect.mo-cflags = $(USB_REDIR_CFLAGS)
+redirect.mo-libs = $(USB_REDIR_LIBS)
+endif
 endif
 
 # usb pass-through

include/qemu/module.h

@@ -70,5 +70,7 @@ void register_dso_module_init(void (*fn)(void), module_init_type type);
 
 void module_call_init(module_init_type type);
 bool module_load_one(const char *prefix, const char *lib_name);
+void module_load_qom_one(const char *type);
+void module_load_qom_all(void);
 
 #endif

include/qom/object.h

@@ -994,6 +994,18 @@ bool object_class_is_abstract(ObjectClass *klass);
  */
 ObjectClass *object_class_by_name(const char *typename);
 
+/**
+ * module_object_class_by_name:
+ * @typename: The QOM typename to obtain the class for.
+ *
+ * For objects which might be provided by a module.  Behaves like
+ * object_class_by_name, but additionally tries to load the module
+ * needed in case the class is not available.
+ *
+ * Returns: The class for @typename or %NULL if not found.
+ */
+ObjectClass *module_object_class_by_name(const char *typename);
+
 void object_class_foreach(void (*fn)(ObjectClass *klass, void *opaque),
                           const char *implements_type, bool include_abstract,
                           void *opaque);

qdev-monitor.c

@@ -149,6 +149,7 @@ static void qdev_print_devinfos(bool show_no_user)
     int i;
     bool cat_printed;
 
+    module_load_qom_all();
     list = object_class_get_list_sorted(TYPE_DEVICE, false);
 
     for (i = 0; i <= DEVICE_CATEGORY_MAX; i++) {
@@ -217,13 +218,13 @@ static DeviceClass *qdev_get_device_class(const char **driver, Error **errp)
     DeviceClass *dc;
     const char *original_name = *driver;
 
-    oc = object_class_by_name(*driver);
+    oc = module_object_class_by_name(*driver);
     if (!oc) {
         const char *typename = find_typename_by_alias(*driver);
 
         if (typename) {
             *driver = typename;
-            oc = object_class_by_name(*driver);
+            oc = module_object_class_by_name(*driver);
         }
     }
 

qom/object.c

@@ -985,6 +985,20 @@ ObjectClass *object_class_by_name(const char *typename)
     return type->class;
 }
 
+ObjectClass *module_object_class_by_name(const char *typename)
+{
+    ObjectClass *oc;
+
+    oc = object_class_by_name(typename);
+#ifdef CONFIG_MODULES
+    if (!oc) {
+        module_load_qom_one(typename);
+        oc = object_class_by_name(typename);
+    }
+#endif
+    return oc;
+}
+
 ObjectClass *object_class_get_parent(ObjectClass *class)
 {
     TypeImpl *type = type_get_parent(class->type);

qom/qom-qmp-cmds.c

@@ -116,6 +116,7 @@ ObjectTypeInfoList *qmp_qom_list_types(bool has_implements,
 {
     ObjectTypeInfoList *ret = NULL;
 
+    module_load_qom_all();
     object_class_foreach(qom_list_types_tramp, implements, abstract, &ret);
 
     return ret;
@@ -130,7 +131,7 @@ ObjectPropertyInfoList *qmp_device_list_properties(const char *typename,
     ObjectPropertyIterator iter;
     ObjectPropertyInfoList *prop_list = NULL;
 
-    klass = object_class_by_name(typename);
+    klass = module_object_class_by_name(typename);
     if (klass == NULL) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
                   "Device '%s' not found", typename);

softmmu/vl.c

@@ -1772,8 +1772,8 @@ static bool vga_interface_available(VGAInterfaceType t)
 
     assert(t < VGA_TYPE_MAX);
     return !ti->class_names[0] ||
-           object_class_by_name(ti->class_names[0]) ||
+           module_object_class_by_name(ti->class_names[0]) ||
-           object_class_by_name(ti->class_names[1]);
+           module_object_class_by_name(ti->class_names[1]);
 }
 
 static const char *

util/module.c

@@ -245,3 +245,70 @@ bool module_load_one(const char *prefix, const char *lib_name)
 #endif
     return success;
 }
+
+/*
+ * Building devices and other qom objects modular is mostly useful in
+ * case they have dependencies to external shared libraries, so we can
+ * cut down the core qemu library dependencies.  Which is the case for
+ * only a very few devices & objects.
+ *
+ * So with the expectation that this will be rather the exception than
+ * to rule and the list will not gain that many entries go with a
+ * simple manually maintained list for now.
+ */
+static struct {
+    const char *type;
+    const char *prefix;
+    const char *module;
+} const qom_modules[] = {
+    { "ccid-card-passthru",    "hw-", "usb-smartcard"         },
+    { "ccid-card-emulated",    "hw-", "usb-smartcard"         },
+    { "usb-redir",             "hw-", "usb-redirect"          },
+    { "qxl-vga",               "hw-", "display-qxl"           },
+    { "qxl",                   "hw-", "display-qxl"           },
+    { "virtio-gpu-device",     "hw-", "display-virtio-gpu"    },
+    { "virtio-gpu-pci",        "hw-", "display-virtio-gpu"    },
+    { "virtio-vga",            "hw-", "display-virtio-gpu"    },
+    { "vhost-user-gpu-device", "hw-", "display-virtio-gpu"    },
+    { "vhost-user-gpu-pci",    "hw-", "display-virtio-gpu"    },
+    { "vhost-user-vga",        "hw-", "display-virtio-gpu"    },
+    { "chardev-braille",       "chardev-", "baum"             },
+};
+
+static bool module_loaded_qom_all;
+
+void module_load_qom_one(const char *type)
+{
+    int i;
+
+    if (module_loaded_qom_all) {
+        return;
+    }
+    for (i = 0; i < ARRAY_SIZE(qom_modules); i++) {
+        if (strcmp(qom_modules[i].type, type) == 0) {
+            module_load_one(qom_modules[i].prefix,
+                            qom_modules[i].module);
+            return;
+        }
+    }
+}
+
+void module_load_qom_all(void)
+{
+    int i;
+
+    if (module_loaded_qom_all) {
+        return;
+    }
+    for (i = 0; i < ARRAY_SIZE(qom_modules); i++) {
+        if (i > 0 && (strcmp(qom_modules[i - 1].module,
+                             qom_modules[i].module) == 0 &&
+                      strcmp(qom_modules[i - 1].prefix,
+                             qom_modules[i].prefix) == 0)) {
+            /* one module implementing multiple types -> load only once */
+            continue;
+        }
+        module_load_one(qom_modules[i].prefix, qom_modules[i].module);
+    }
+    module_loaded_qom_all = true;
+}