block: Add block job transactions

Sometimes block jobs must execute as a transaction group.  Finishing
jobs wait until all other jobs are ready to complete successfully.
Failure or cancellation of one job cancels the other jobs in the group.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1446765200-3054-10-git-send-email-jsnow@redhat.com
[Rewrite the implementation which is now contained in block_job_completed.
--Fam]
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

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

2 files changed, 39 insertions, 0 deletions

diff --git a/include/block/block.h b/include/block/block.h
index 92f6f6a95a..73edb1a79c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -14,6 +14,7 @@ typedef struct BlockDriver BlockDriver;
 typedef struct BlockJob BlockJob;
 typedef struct BdrvChild BdrvChild;
 typedef struct BdrvChildRole BdrvChildRole;
+typedef struct BlockJobTxn BlockJobTxn;
 
 typedef struct BlockDriverInfo {
     /* in bytes, 0 if irrelevant */
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index c70d55a644..d84ccd8d2c 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -162,6 +162,9 @@ struct BlockJob {
      */
     int ret;
 
+    /** Non-NULL if this job is part of a transaction */
+    BlockJobTxn *txn;
+    QLIST_ENTRY(BlockJob) txn_list;
 };
 
 /**
@@ -405,4 +408,39 @@ void block_job_defer_to_main_loop(BlockJob *job,
                                   BlockJobDeferToMainLoopFn *fn,
                                   void *opaque);
 
+/**
+ * block_job_txn_new:
+ *
+ * Allocate and return a new block job transaction.  Jobs can be added to the
+ * transaction using block_job_txn_add_job().
+ *
+ * The transaction is automatically freed when the last job completes or is
+ * cancelled.
+ *
+ * All jobs in the transaction either complete successfully or fail/cancel as a
+ * group.  Jobs wait for each other before completing.  Cancelling one job
+ * cancels all jobs in the transaction.
+ */
+BlockJobTxn *block_job_txn_new(void);
+
+/**
+ * block_job_txn_unref:
+ *
+ * Release a reference that was previously acquired with block_job_txn_add_job
+ * or block_job_txn_new. If it's the last reference to the object, it will be
+ * freed.
+ */
+void block_job_txn_unref(BlockJobTxn *txn);
+
+/**
+ * block_job_txn_add_job:
+ * @txn: The transaction (may be NULL)
+ * @job: Job to add to the transaction
+ *
+ * Add @job to the transaction.  The @job must not already be in a transaction.
+ * The caller must call either block_job_txn_unref() or block_job_completed()
+ * to release the reference that is automatically grabbed here.
+ */
+void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job);
+
 #endif