[PATCH 1/3] mirror: Set s->base_overlay only if s->base is set

[Max Reitz <mreitz@redhat.com>]

This way, sync=full will not need a reference to any node other than the
source and the target.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/mirror.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 26acf4af6f..11ebffdf99 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -42,6 +42,7 @@ typedef struct MirrorBlockJob {
     BlockBackend *target;
     BlockDriverState *mirror_top_bs;
     BlockDriverState *base;
+    /* Overlay of @base if @base is non-NULL; NULL otherwise */
     BlockDriverState *base_overlay;
 
     /* The name of the graph node to replace */
@@ -839,8 +840,9 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             return 0;
         }
 
-        ret = bdrv_is_allocated_above(bs, s->base_overlay, true, offset, bytes,
-                                      &count);
+        ret = bdrv_is_allocated_above(bs, s->base_overlay,
+                                      s->base_overlay != NULL,
+                                      offset, bytes, &count);
         if (ret < 0) {
             return ret;
         }
@@ -1710,7 +1712,7 @@ static BlockJob *mirror_start_job(
     s->zero_target = zero_target;
     s->copy_mode = copy_mode;
     s->base = base;
-    s->base_overlay = bdrv_find_overlay(bs, base);
+    s->base_overlay = base ? bdrv_find_overlay(bs, base) : NULL;
     s->granularity = granularity;
     s->buf_size = ROUND_UP(buf_size, granularity);
     s->unmap = unmap;
-- 
2.26.2