[PATCH v2] hw/nubus/nubus-virtio-mmio: Fix missing ERRP_GUARD() in nubus_virtio_mmio_realize()

[Zhao Liu <zhao1.liu@intel.com>]

According to the comment in qapi/error.h, dereferencing @errp requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
* - It must not be dereferenced, because it may be null.
...
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.
*
* Using it when it's not needed is safe, but please avoid cluttering
* the source with useless code.

In nubus_virtio_mmio_realize(), @errp is dereferenced without
ERRP_GUARD().

Although nubus_virtio_mmio_realize() - as a DeviceClass.realize()
method - is never passed a null @errp argument, it should follow the
rules on @errp usage.  Add the ERRP_GUARD() there.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
v2: Used Markus' words in commit message and added his r/b tag.
---
 hw/nubus/nubus-virtio-mmio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/nubus/nubus-virtio-mmio.c b/hw/nubus/nubus-virtio-mmio.c
index 58a63c84d0be..a5558d3ec28b 100644
--- a/hw/nubus/nubus-virtio-mmio.c
+++ b/hw/nubus/nubus-virtio-mmio.c
@@ -23,6 +23,7 @@ static void nubus_virtio_mmio_set_input_irq(void *opaque, int n, int level)
 
 static void nubus_virtio_mmio_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     NubusVirtioMMIODeviceClass *nvmdc = NUBUS_VIRTIO_MMIO_GET_CLASS(dev);
     NubusVirtioMMIO *s = NUBUS_VIRTIO_MMIO(dev);
     NubusDevice *nd = NUBUS_DEVICE(dev);
-- 
2.34.1