block/qcow2-refcount: add trace-point to qcow2_process_discards

Let's at least trace ignored failure.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

@@ -29,6 +29,7 @@
 #include "qemu/range.h"
 #include "qemu/bswap.h"
 #include "qemu/cutils.h"
+#include "trace.h"
 
 static int64_t alloc_clusters_noref(BlockDriverState *bs, uint64_t size,
                                     uint64_t max);
@@ -737,7 +738,11 @@ void qcow2_process_discards(BlockDriverState *bs, int ret)
 
         /* Discard is optional, ignore the return value */
         if (ret >= 0) {
-            bdrv_pdiscard(bs->file, d->offset, d->bytes);
+            int r2 = bdrv_pdiscard(bs->file, d->offset, d->bytes);
+            if (r2 < 0) {
+                trace_qcow2_process_discards_failed_region(d->offset, d->bytes,
+                                                           r2);
+            }
         }
 
         g_free(d);