[RFC PATCH 1/3] qom: Always register FW_CFG_DATA_GENERATOR_INTERFACE

[Philippe Mathieu-Daudé]

While the FW_CFG_DATA_GENERATOR_INTERFACE is only consumed
by a device only available using system-mode (fw_cfg), it is
implemented by a crypto component (tls-cipher-suites) which
is always available when crypto is used.

Commit 69699f3055 introduced the following error in the
qemu-storage-daemon binary:

  $ echo -e \
    '{"execute": "qmp_capabilities"}\r\n{"execute": 
"qom-list-types"}\r\n{"execute": "quit"}\r\n' \
    | storage-daemon/qemu-storage-daemon --chardev stdio,id=qmp0  --monitor qmp0
  {"QMP": {"version": {"qemu": {"micro": 50, "minor": 1, "major": 5}, 
"package": ""}, "capabilities": ["oob"]}}
  {"return": {}}
  missing interface 'fw_cfg-data-generator' for object 'tls-creds'
  Aborted (core dumped)

Since QOM dependencies are resolved at runtime, this issue
could not be triggered at linktime, and we don't have test
running the qemu-storage-daemon binary.

Fix by always registering the QOM interface.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Fixes: 69699f3055 ("crypto/tls-cipher-suites: Produce fw_cfg consumable blob")
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
I first used:

+if config_host.has_key('CONFIG_GNUTLS') or have_system
+  qom_ss.add(files('fw_cfg_interface.c'))
+endif

but then realized anything could implement a QOM interface,
so better keep this generic.
---
 hw/nvram/fw_cfg.c      |  7 -------
 qom/fw_cfg_interface.c | 15 +++++++++++++++
 MAINTAINERS            |  1 +
 qom/meson.build        |  5 +++++
 4 files changed, 21 insertions(+), 7 deletions(-)
 create mode 100644 qom/fw_cfg_interface.c

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 0e95d057fd..08539a1aab 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -1360,18 +1360,11 @@ static const TypeInfo fw_cfg_mem_info = {
     .class_init    = fw_cfg_mem_class_init,
 };
 
-static const TypeInfo fw_cfg_data_generator_interface_info = {
-    .parent = TYPE_INTERFACE,
-    .name = TYPE_FW_CFG_DATA_GENERATOR_INTERFACE,
-    .class_size = sizeof(FWCfgDataGeneratorClass),
-};
-
 static void fw_cfg_register_types(void)
 {
     type_register_static(&fw_cfg_info);
     type_register_static(&fw_cfg_io_info);
     type_register_static(&fw_cfg_mem_info);
-    type_register_static(&fw_cfg_data_generator_interface_info);
 }
 
 type_init(fw_cfg_register_types)
diff --git a/qom/fw_cfg_interface.c b/qom/fw_cfg_interface.c
new file mode 100644
index 0000000000..2b19502ffe
--- /dev/null
+++ b/qom/fw_cfg_interface.c
@@ -0,0 +1,15 @@
+#include "qemu/osdep.h"
+#include "hw/nvram/fw_cfg.h"
+
+static const TypeInfo fw_cfg_data_generator_interface_info = {
+    .parent = TYPE_INTERFACE,
+    .name = TYPE_FW_CFG_DATA_GENERATOR_INTERFACE,
+    .class_size = sizeof(FWCfgDataGeneratorClass),
+};
+
+static void fw_cfg_register_types(void)
+{
+    type_register_static(&fw_cfg_data_generator_interface_info);
+}
+
+type_init(fw_cfg_register_types)
diff --git a/MAINTAINERS b/MAINTAINERS
index b76fb31861..9c89d54b41 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2055,6 +2055,7 @@ R: Gerd Hoffmann <kraxel@redhat.com>
 S: Supported
 F: docs/specs/fw_cfg.txt
 F: hw/nvram/fw_cfg.c
+F: qom/fw_cfg_interface.c
 F: stubs/fw_cfg.c
 F: include/hw/nvram/fw_cfg.h
 F: include/standard-headers/linux/qemu_fw_cfg.h
diff --git a/qom/meson.build b/qom/meson.build
index a1cd03c82c..7335f8c8a2 100644
--- a/qom/meson.build
+++ b/qom/meson.build
@@ -7,6 +7,11 @@ qom_ss.add(files(
   'qom-qobject.c',
 ))
 
+# interfaces any object might implement
+qom_ss.add(files(
+  'fw_cfg_interface.c',
+))
+
 qmp_ss.add(files('qom-qmp-cmds.c'))
 softmmu_ss.add(files('qom-hmp-cmds.c'))
 
-- 
2.26.2