Presently, we abort transactions in the same order they were processed in.
Bitmap commands, though, attempt to restore backup data structures on abort.
To that end, though, they need to be aborted in reverse chronological order.

Replace the QSIMPLEQ data structure with a QTAILQ one, so we can iterate
in reverse for the abort phase of the transaction.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 blockdev.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 81f95d920b..1ba706df8b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1341,7 +1341,7 @@ struct BlkActionState {
     const BlkActionOps *ops;
     JobTxn *block_job_txn;
     TransactionProperties *txn_props;
-    QSIMPLEQ_ENTRY(BlkActionState) entry;
+    QTAILQ_ENTRY(BlkActionState) entry;
 };
 
 /* internal snapshot private data */
@@ -2269,8 +2269,8 @@ void qmp_transaction(TransactionActionList *dev_list,
     BlkActionState *state, *next;
     Error *local_err = NULL;
 
-    QSIMPLEQ_HEAD(snap_bdrv_states, BlkActionState) snap_bdrv_states;
-    QSIMPLEQ_INIT(&snap_bdrv_states);
+    QTAILQ_HEAD(snap_bdrv_states, BlkActionState) snap_bdrv_states;
+    QTAILQ_INIT(&snap_bdrv_states);
 
     /* Does this transaction get canceled as a group on failure?
      * If not, we don't really need to make a JobTxn.
@@ -2301,7 +2301,7 @@ void qmp_transaction(TransactionActionList *dev_list,
         state->action = dev_info;
         state->block_job_txn = block_job_txn;
         state->txn_props = props;
-        QSIMPLEQ_INSERT_TAIL(&snap_bdrv_states, state, entry);
+        QTAILQ_INSERT_TAIL(&snap_bdrv_states, state, entry);
 
         state->ops->prepare(state, &local_err);
         if (local_err) {
@@ -2310,7 +2310,7 @@ void qmp_transaction(TransactionActionList *dev_list,
         }
     }
 
-    QSIMPLEQ_FOREACH(state, &snap_bdrv_states, entry) {
+    QTAILQ_FOREACH(state, &snap_bdrv_states, entry) {
         if (state->ops->commit) {
             state->ops->commit(state);
         }
@@ -2321,13 +2321,13 @@ void qmp_transaction(TransactionActionList *dev_list,
 
 delete_and_fail:
     /* failure, and it is all-or-none; roll back all operations */
-    QSIMPLEQ_FOREACH(state, &snap_bdrv_states, entry) {
+    QTAILQ_FOREACH_REVERSE(state, &snap_bdrv_states, snap_bdrv_states, entry) {
         if (state->ops->abort) {
             state->ops->abort(state);
         }
     }
 exit:
-    QSIMPLEQ_FOREACH_SAFE(state, &snap_bdrv_states, entry, next) {
+    QTAILQ_FOREACH_SAFE(state, &snap_bdrv_states, entry, next) {
         if (state->ops->clean) {
             state->ops->clean(state);
         }
-- 
2.17.2