From aa47e92291e85e7d2909e2c0d9083d607f501cc8 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 3 Oct 2022 13:43:14 +0200
Subject: Omit USB QEMU options if custom options are provided

---
 bbot/agent/machine.cxx | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/bbot/agent/machine.cxx b/bbot/agent/machine.cxx
index 83e64e5..e7f549d 100644
--- a/bbot/agent/machine.cxx
+++ b/bbot/agent/machine.cxx
@@ -309,10 +309,10 @@ namespace bbot
     }
     else
     {
-      auto add = [&os] (string o, string v)
+      auto add = [&os] (string o, optional<string> v = {})
       {
         os.push_back (move (o));
-        os.push_back (move (v));
+        if (v) os.push_back (move (*v));
       };
 
       // Network.
@@ -334,6 +334,17 @@ namespace bbot
       //"-drive",  "if=none,id=disk0,format=raw,file=disk.img"
       //"-device", "virtio-scsi-pci,id=scsi"
       //"-device", "scsi-hd,drive=disk0"
+
+      // USB settings.
+      //
+      // These options should make graphical VMs usable from VNC.
+      //
+      // Note that the "standard" USB bus may not be available on
+      // architectures other than x86 (e.g., aarch64).
+      //
+      add ("-usb");
+      add ("-device", "usb-kbd");
+      add ("-device", "usb-tablet");
     }
 
     // Setup QMP (QEMU Machine Protocol) monitor to act as a log.
@@ -388,12 +399,6 @@ namespace bbot
       "-global", "kvm-pit.lost_tick_policy=discard",
 #endif
 
-      // USB settings.
-      //
-      // This option should make graphical VMs usable from VNC.
-      //
-      "-usb", "-device", "usb-kbd", "-device", "usb-tablet",
-
       // These can override the above but not below.
       //
       os,
-- 
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