[Qemu-devel] [PATCH v4 10/13] block: Simplify bdrv_append_temp_snapshot() logic

[Eric Blake <eblake@redhat.com>]

Noticed while checking Coccinelle results. Naming a label 'out:'
when it is only used on error paths is weird.  Also, we had some
dead stores to 'ret'.  Meanwhile we know that snapshot_options
is NULL on success and that QDECREF(NULL) is safe.  So merge the
two exit paths into one by careful control over bs_snapshot.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v4: fix -O2 compilation bug, kill dead 'ret'
v3: split out from bigger v2 patch
---
 block.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/block.c b/block.c
index c8a6bce..2bf3d40 100644
--- a/block.c
+++ b/block.c
@@ -2158,7 +2158,7 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
     char *tmp_filename = g_malloc0(PATH_MAX + 1);
     int64_t total_size;
     QemuOpts *opts = NULL;
-    BlockDriverState *bs_snapshot;
+    BlockDriverState *bs_snapshot = NULL;
     Error *local_err = NULL;
     int ret;

@@ -2198,28 +2198,25 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
     bs_snapshot = bdrv_open(NULL, NULL, snapshot_options, flags, errp);
     snapshot_options = NULL;
     if (!bs_snapshot) {
-        ret = -EINVAL;
         goto out;
     }

-    /* bdrv_append() consumes a strong reference to bs_snapshot (i.e. it will
-     * call bdrv_unref() on it), so in order to be able to return one, we have
-     * to increase bs_snapshot's refcount here */
+    /* bdrv_append() consumes a strong reference to bs_snapshot
+     * (i.e. it will call bdrv_unref() on it) even on error, so in
+     * order to be able to return one, we have to increase
+     * bs_snapshot's refcount here */
     bdrv_ref(bs_snapshot);
     bdrv_append(bs_snapshot, bs, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
-        ret = -EINVAL;
+        bs_snapshot = NULL;
         goto out;
     }

+out:
+    QDECREF(snapshot_options);
     g_free(tmp_filename);
     return bs_snapshot;
-
-out:
-    QDECREF(snapshot_options);
-    g_free(tmp_filename);
-    return NULL;
 }

 /*
-- 
2.9.3