[Qemu-devel] [PATCH v2 for-2.7 2/8] block: Let bdrv_open_inherit() return the snapshot

[Max Reitz]

If bdrv_open_inherit() creates a snapshot BDS and *pbs is NULL, that
snapshot BDS should be returned instead of the BDS under it.

To this end, bdrv_append_temp_snapshot() now returns the snapshot BDS
instead of just appending it on top of the snapshotted BDS. Also, it
calls bdrv_ref() before bdrv_append() (which bdrv_open_inherit() has to
undo if not returning the overlay).

Signed-off-by: Max Reitz <address@hidden>
---
 block.c | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/block.c b/block.c
index b6a452a..d222227 100644
--- a/block.c
+++ b/block.c
@@ -1424,8 +1424,10 @@ done:
     return c;
 }
 
-static int bdrv_append_temp_snapshot(BlockDriverState *bs, int flags,
-                                     QDict *snapshot_options, Error **errp)
+static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
+                                                   int flags,
+                                                   QDict *snapshot_options,
+                                                   Error **errp)
 {
     /* TODO: extra byte is a hack to ensure MAX_PATH space on Windows. */
     char *tmp_filename = g_malloc0(PATH_MAX + 1);
@@ -1441,7 +1443,6 @@ static int bdrv_append_temp_snapshot(BlockDriverState 
*bs, int flags,
     /* Get the required size from the image */
     total_size = bdrv_getlength(bs);
     if (total_size < 0) {
-        ret = total_size;
         error_setg_errno(errp, -total_size, "Could not get image size");
         goto out;
     }
@@ -1481,12 +1482,16 @@ static int bdrv_append_temp_snapshot(BlockDriverState 
*bs, int flags,
         goto out;
     }
 
+    bdrv_ref(bs_snapshot);
     bdrv_append(bs_snapshot, bs);
 
+    g_free(tmp_filename);
+    return bs_snapshot;
+
 out:
     QDECREF(snapshot_options);
     g_free(tmp_filename);
-    return ret;
+    return NULL;
 }
 
 /*
@@ -1705,17 +1710,31 @@ static int bdrv_open_inherit(BlockDriverState **pbs, 
const char *filename,
     }
 
     QDECREF(options);
-    *pbs = bs;
 
     /* For snapshot=on, create a temporary qcow2 overlay. bs points to the
      * temporary snapshot afterwards. */
     if (snapshot_flags) {
-        ret = bdrv_append_temp_snapshot(bs, snapshot_flags, snapshot_options,
-                                        &local_err);
+        BlockDriverState *snapshot_bs;
+        snapshot_bs = bdrv_append_temp_snapshot(bs, snapshot_flags,
+                                                snapshot_options, &local_err);
         snapshot_options = NULL;
         if (local_err) {
+            ret = -EINVAL;
             goto close_and_fail;
         }
+        if (!*pbs) {
+            /* The reference is now held by the overlay BDS */
+            bdrv_unref(bs);
+            bs = snapshot_bs;
+        } else {
+            /* It is still referenced in the same way that *pbs was referenced,
+             * however that may be */
+            bdrv_unref(snapshot_bs);
+        }
+    }
+
+    if (!*pbs) {
+        *pbs = bs;
     }
 
     return 0;
-- 
2.8.0