[PATCH] hw/virtio/vdpa-dev: Check returned value instead of dereferencing @errp

[Zhao Liu]

As the comment in qapi/error, 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.

Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
context and won't get NULL @errp, it's still better to follow the
requirement to add the ERRP_GUARD().

But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
distinguish between successful and unsuccessful calls, so check the
return values directly without dereferencing @errp, which eliminates
the need of ERRP_GUARD().

Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: "Eugenio Pérez" <epere...@redhat.com>
Cc: Jason Wang <jasow...@redhat.com>
Signed-off-by: Zhao Liu <zhao1....@intel.com>
---
 hw/virtio/vdpa-dev.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
index 64b96b226c39..7b439efdc1d3 100644
--- a/hw/virtio/vdpa-dev.c
+++ b/hw/virtio/vdpa-dev.c
@@ -50,6 +50,7 @@ vhost_vdpa_device_get_u32(int fd, unsigned long int cmd, 
Error **errp)
 
 static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VhostVdpaDevice *v = VHOST_VDPA_DEVICE(vdev);
     struct vhost_vdpa_iova_range iova_range;
@@ -63,19 +64,19 @@ static void vhost_vdpa_device_realize(DeviceState *dev, 
Error **errp)
     }
 
     v->vhostfd = qemu_open(v->vhostdev, O_RDWR, errp);
-    if (*errp) {
+    if (v->vhostfd < 0) {
         return;
     }
 
     v->vdev_id = vhost_vdpa_device_get_u32(v->vhostfd,
                                            VHOST_VDPA_GET_DEVICE_ID, errp);
-    if (*errp) {
+    if (v->vdev_id < 0) {
         goto out;
     }
 
     max_queue_size = vhost_vdpa_device_get_u32(v->vhostfd,
                                                VHOST_VDPA_GET_VRING_NUM, errp);
-    if (*errp) {
+    if (max_queue_size < 0) {
         goto out;
     }
 
@@ -89,7 +90,7 @@ static void vhost_vdpa_device_realize(DeviceState *dev, Error 
**errp)
 
     v->num_queues = vhost_vdpa_device_get_u32(v->vhostfd,
                                               VHOST_VDPA_GET_VQS_COUNT, errp);
-    if (*errp) {
+    if (v->num_queues < 0) {
         goto out;
     }
 
@@ -127,7 +128,7 @@ static void vhost_vdpa_device_realize(DeviceState *dev, 
Error **errp)
     v->config_size = vhost_vdpa_device_get_u32(v->vhostfd,
                                                VHOST_VDPA_GET_CONFIG_SIZE,
                                                errp);
-    if (*errp) {
+    if (v->config_size < 0) {
         goto vhost_cleanup;
     }
 
-- 
2.34.1