[Qemu-devel] [PATCH 2/3] backup: fix transaction fail scenario

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

When there are several backups in one transaction, successed block job
must wait for possible cancelling by other block job (if it fails).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/backup.c           | 12 ++++++++++++
 blockdev.c               |  2 ++
 blockjob.c               | 33 +++++++++++++++++++++++++++++++++
 include/block/blockjob.h | 10 ++++++++++
 4 files changed, 57 insertions(+)

diff --git a/block/backup.c b/block/backup.c
index 2c05323..9198a40 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -467,6 +467,18 @@ static void coroutine_fn backup_run(void *opaque)
     qemu_co_rwlock_unlock(&job->flush_rwlock);
     g_free(job->done_bitmap);
 
+    if (ret == 0) {
+        job->common.success = true;
+        while (!block_job_txn_all_success(&job->common)) {
+            if (block_job_is_cancelled(&job->common)) {
+                break;
+            }
+
+            block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, SLICE_TIME);
+        }
+    }
+
+
     bdrv_op_unblock_all(blk_bs(target), job->common.blocker);
 
     data = g_malloc(sizeof(*data));
diff --git a/blockdev.c b/blockdev.c
index 384ad3b..59ae9e4 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2250,6 +2250,8 @@ void qmp_transaction(TransactionActionList *dev_list,
         }
     }
 
+    block_job_txn_set_prepared(block_job_txn);
+
     QSIMPLEQ_FOREACH(state, &snap_bdrv_states, entry) {
         if (state->ops->commit) {
             state->ops->commit(state);
diff --git a/blockjob.c b/blockjob.c
index e045091..a85844d 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -49,6 +49,8 @@ struct BlockJobTxn {
 
     /* Reference count */
     int refcnt;
+
+    bool prepared;
 };
 
 static QLIST_HEAD(, BlockJob) block_jobs = QLIST_HEAD_INITIALIZER(block_jobs);
@@ -222,6 +224,28 @@ static void block_job_completed_single(BlockJob *job)
     block_job_unref(job);
 }
 
+bool block_job_txn_all_success(BlockJob *job)
+{
+    BlockJobTxn *txn = job->txn;
+    BlockJob *other_job;
+
+    if (txn == NULL) {
+        return job->success;
+    }
+
+    if (!txn->prepared) {
+        return false;
+    }
+
+    QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
+        if (!(other_job->success)) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
 static void block_job_completed_txn_abort(BlockJob *job)
 {
     AioContext *ctx;
@@ -662,3 +686,12 @@ void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job)
     QLIST_INSERT_HEAD(&txn->jobs, job, txn_list);
     block_job_txn_ref(txn);
 }
+
+void block_job_txn_set_prepared(BlockJobTxn *txn)
+{
+    if (!txn) {
+        return;
+    }
+
+    txn->prepared = true;
+}
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 4ddb4ae..41f56b4 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -156,6 +156,13 @@ struct BlockJob {
     bool ready;
 
     /**
+     * All work is done with success, job is ready to be completed
+     * successfully, but waiting for cancelling by other job from transaction,
+     * if it (other job) fails.
+     */
+    bool success;
+
+    /**
      * Set to true when the job has deferred work to the main loop.
      */
     bool deferred_to_main_loop;
@@ -504,4 +511,7 @@ void block_job_txn_unref(BlockJobTxn *txn);
  */
 void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job);
 
+void block_job_txn_set_prepared(BlockJobTxn *txn);
+bool block_job_txn_all_success(BlockJob *job);
+
 #endif
-- 
1.8.3.1