[PATCH 2/2] hw/usb: Do not build USB subsystem if not required

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

If the Kconfig 'USB' value is not selected, it is pointless to
build the USB core components. Add a stub for the HMP commands
and usbdevice_create() which is called by usb_device_add in
softmmu/vl.c.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 stubs/usb-dev-stub.c | 25 +++++++++++++++++++++++++
 MAINTAINERS          |  1 +
 hw/usb/meson.build   |  9 +++------
 stubs/meson.build    |  1 +
 4 files changed, 30 insertions(+), 6 deletions(-)
 create mode 100644 stubs/usb-dev-stub.c

diff --git a/stubs/usb-dev-stub.c b/stubs/usb-dev-stub.c
new file mode 100644
index 00000000000..b1adeeb4548
--- /dev/null
+++ b/stubs/usb-dev-stub.c
@@ -0,0 +1,25 @@
+/*
+ * QEMU USB device emulation stubs
+ *
+ * Copyright (C) 2021 Philippe Mathieu-Daudé <f4bug@amsat.org>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/error-report.h"
+#include "sysemu/sysemu.h"
+#include "monitor/monitor.h"
+#include "hw/usb.h"
+
+USBDevice *usbdevice_create(const char *driver)
+{
+    error_report("Support for USB devices not built-in");
+
+    return NULL;
+}
+
+void hmp_info_usb(Monitor *mon, const QDict *qdict)
+{
+    monitor_printf(mon, "Support for USB devices not built-in\n");
+}
diff --git a/MAINTAINERS b/MAINTAINERS
index 36055f14c59..cd63d3efd8b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1804,6 +1804,7 @@ USB
 M: Gerd Hoffmann <kraxel@redhat.com>
 S: Maintained
 F: hw/usb/*
+F: stubs/usb-dev-stub.c
 F: tests/qtest/usb-*-test.c
 F: docs/usb2.txt
 F: docs/usb-storage.txt
diff --git a/hw/usb/meson.build b/hw/usb/meson.build
index fb7a74e73ae..f357270d0b6 100644
--- a/hw/usb/meson.build
+++ b/hw/usb/meson.build
@@ -1,17 +1,14 @@
 hw_usb_modules = {}
 
 # usb subsystem core
-softmmu_ss.add(files(
+softmmu_ss.add(when: 'CONFIG_USB', if_true: files(
   'bus.c',
   'combined-packet.c',
   'core.c',
-  'pcap.c',
-  'libhw.c'
-))
-
-softmmu_ss.add(when: 'CONFIG_USB', if_true: files(
   'desc.c',
   'desc-msos.c',
+  'libhw.c',
+  'pcap.c',
 ))
 
 # usb host adapters
diff --git a/stubs/meson.build b/stubs/meson.build
index be6f6d609e5..3faef16892b 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -50,6 +50,7 @@
 endif
 if have_system
   stub_ss.add(files('semihost.c'))
+  stub_ss.add(files('usb-dev-stub.c'))
   stub_ss.add(files('xen-hw-stub.c'))
 else
   stub_ss.add(files('qdev.c'))
-- 
2.26.3