[PATCH 07/16] block/qcow2-bitmap: Fix missing ERRP_GUARD() for error_prepend()

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

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 qcow2_co_can_store_new_dirty_bitmap() passes @errp to
error_prepend(). As a BlockDriver.bdrv_co_can_store_new_dirty_bitmap
method, it's called by bdrv_co_can_store_new_dirty_bitmap().

Its caller is not being called anywhere, but as the API in
include/block/block-io.h, we can't ensure what kind of @errp future
users will pass in.

To avoid potential issues as [1] said, add missing ERRP_GUARD() at the
beginning of qcow2_co_can_store_new_dirty_bitmap().

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

Cc: Eric Blake <eblake@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Cc: John Snow <jsnow@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 block/qcow2-bitmap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index 0e567ed588d7..874ea5694851 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -1710,6 +1710,7 @@ bool coroutine_fn qcow2_co_can_store_new_dirty_bitmap(BlockDriverState *bs,
                                                       uint32_t granularity,
                                                       Error **errp)
 {
+    ERRP_GUARD();
     BDRVQcow2State *s = bs->opaque;
     BdrvDirtyBitmap *bitmap;
     uint64_t bitmap_directory_size = 0;
-- 
2.34.1