[PATCH v2 24/29] hw/vfio/platform: 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 &error_fatal, the user
can't see this additional information, because exit() happens in
error_setg earlier than information is added [1].

The vfio_platform_realize() passes @errp to error_prepend(), and as a
DeviceClass.realize method, there are too many possible callers to check
the impact of this defect; it may or may not be harmless. Thus it is
necessary to protect @errp with ERRP_GUARD().

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: Alex Williamson <alex.williamson@redhat.com>
Cc: "Cédric Le Goater" <clg@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
---
v2: Use Markus' sentence to polish commit message. (Markus)
---
 hw/vfio/platform.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
index a8d9b7da633e..dcd2365fb353 100644
--- a/hw/vfio/platform.c
+++ b/hw/vfio/platform.c
@@ -576,6 +576,7 @@ static int vfio_base_device_init(VFIODevice *vbasedev, 
Error **errp)
  */
 static void vfio_platform_realize(DeviceState *dev, Error **errp)
 {
+    ERRP_GUARD();
     VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(dev);
     SysBusDevice *sbdev = SYS_BUS_DEVICE(dev);
     VFIODevice *vbasedev = &vdev->vbasedev;
-- 
2.34.1