[PATCH 04/17] hw/scsi/vhost-scsi: Fix missing ERRP_GUARD() for error_prepend()

[Zhao Liu]

From: Zhao Liu <zhao1.liu@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* 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.

ERRP_GUARD() could avoid the case when @errp is the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

The vhost_scsi_realize() passes @errp to error_prepend(), and as a
VirtioDeviceClass.realize method, its @errp is from DeviceClass.realize
so that there is no guarantee that the @errp won't point to
@error_fatal.

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Fam Zheng <fam@euphon.net>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 hw/scsi/vhost-scsi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
index 58a00336c2db..ae26bc19a457 100644
--- a/hw/scsi/vhost-scsi.c
+++ b/hw/scsi/vhost-scsi.c
@@ -220,6 +220,7 @@ static int vhost_scsi_set_workers(VHostSCSICommon *vsc, 
bool per_virtqueue)
 
 static void vhost_scsi_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(dev);
     VHostSCSICommon *vsc = VHOST_SCSI_COMMON(dev);
     Error *err = NULL;
-- 
2.34.1