blockjobs: add block_job_txn_apply function

Simply apply a function transaction-wide.
A few more uses of this in forthcoming patches.

Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockjob.c

@@ -487,6 +487,19 @@ static void block_job_cancel_async(BlockJob *job)
     job->cancelled = true;
 }
 
+static void block_job_txn_apply(BlockJobTxn *txn, void fn(BlockJob *))
+{
+    AioContext *ctx;
+    BlockJob *job, *next;
+
+    QLIST_FOREACH_SAFE(job, &txn->jobs, txn_list, next) {
+        ctx = blk_get_aio_context(job->blk);
+        aio_context_acquire(ctx);
+        fn(job);
+        aio_context_release(ctx);
+    }
+}
+
 static int block_job_finish_sync(BlockJob *job,
                                  void (*finish)(BlockJob *, Error **errp),
                                  Error **errp)
@@ -565,9 +578,8 @@ static void block_job_completed_txn_abort(BlockJob *job)
 
 static void block_job_completed_txn_success(BlockJob *job)
 {
-    AioContext *ctx;
     BlockJobTxn *txn = job->txn;
-    BlockJob *other_job, *next;
+    BlockJob *other_job;
     /*
      * Successful completion, see if there are other running jobs in this
      * txn.
@@ -576,15 +588,10 @@ static void block_job_completed_txn_success(BlockJob *job)
         if (!other_job->completed) {
             return;
         }
-    }
-    /* We are the last completed job, commit the transaction. */
-    QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
-        ctx = blk_get_aio_context(other_job->blk);
-        aio_context_acquire(ctx);
         assert(other_job->ret == 0);
-        block_job_completed_single(other_job);
-        aio_context_release(ctx);
     }
+    /* We are the last completed job, commit the transaction. */
+    block_job_txn_apply(txn, block_job_completed_single);
 }
 
 /* Assumes the block_job_mutex is held */