qdev: Support marking individual buses as 'full'

By default, QEMU will allow devices to be plugged into a bus up to
the bus class's device count limit.  If the user creates a device on
the command line or via the monitor and doesn't explicitly specify
the bus to plug it in, QEMU will plug it into the first non-full bus
that it finds.

This is fine in most cases, but some machines have multiple buses of
a given type, some of which are dedicated to on-board devices and
some of which have an externally exposed connector for user-pluggable
devices. One example is I2C buses.

Provide a new function qbus_mark_full() so that a machine model can
mark this kind of "internal only" bus as 'full' after it has created
all the devices that should be plugged into that bus. The "find a
non-full bus" algorithm will then skip the internal-only bus when
looking for a place to plug in user-created devices.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210903151435.22379-2-peter.maydell@linaro.org

1 files changed, 6 insertions, 1 deletions

diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
index a304754ab9..0705f00846 100644
--- a/softmmu/qdev-monitor.c
+++ b/softmmu/qdev-monitor.c
@@ -435,7 +435,12 @@ static DeviceState *qbus_find_dev(BusState *bus, char *elem)
 
 static inline bool qbus_is_full(BusState *bus)
 {
-    BusClass *bus_class = BUS_GET_CLASS(bus);
+    BusClass *bus_class;
+
+    if (bus->full) {
+        return true;
+    }
+    bus_class = BUS_GET_CLASS(bus);
     return bus_class->max_dev && bus->num_children >= bus_class->max_dev;
 }