[Qemu-devel] [PATCH v3 10/15] block: add block job transactions

[Fam Zheng <famz@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

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>
[Rewrite the implementation which is now contained in block_job_completed.
--Fam]
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockjob.c               | 86 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block.h    |  1 +
 include/block/blockjob.h | 26 +++++++++++++++
 3 files changed, 113 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index e057dd5..7b59b53 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -36,6 +36,16 @@
 #include "qemu/timer.h"
 #include "qapi-event.h"
 
+/* Transactional group of block jobs */
+struct BlockJobTxn {
+
+    /* Is this txn being cancelled? */
+    bool aborting;
+
+    /* List of jobs */
+    QLIST_HEAD(, BlockJob) jobs;
+};
+
 void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
                        int64_t speed, BlockCompletionFunc *cb,
                        void *opaque, Error **errp)
@@ -84,6 +94,59 @@ void block_job_release(BlockDriverState *bs)
     g_free(job);
 }
 
+static void block_job_completed_txn(BlockJobTxn *txn, BlockJob *job, int ret)
+{
+    AioContext *ctx;
+    BlockJob *other_job, *next;
+    if (ret < 0 || block_job_is_cancelled(job)) {
+        if (!txn->aborting) {
+            /* We are the first failed job. Cancel other jobs. */
+            txn->aborting = true;
+            QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
+                if (other_job == job || other_job->completed) {
+                    continue;
+                }
+                ctx = bdrv_get_aio_context(other_job->bs);
+                aio_context_acquire(ctx);
+                block_job_cancel_sync(other_job);
+                assert(other_job->completed);
+                aio_context_release(ctx);
+            }
+            QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
+                if (other_job->driver->txn_abort) {
+                    other_job->driver->txn_abort(other_job);
+                }
+                other_job->cb(other_job->opaque,
+                              other_job->ret ? : -ECANCELED);
+                block_job_release(other_job->bs);
+            }
+        } else {
+            /*
+             * We are cancelled by another job, who will handle everything.
+             */
+            return;
+        }
+    } else {
+        /*
+         * Successful completion, see if there is other running jobs in this
+         * txn. */
+        QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
+            if (!other_job->completed) {
+                return;
+            }
+        }
+        /* We are the last completed job, commit the transaction. */
+        QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
+            if (other_job->driver->txn_commit) {
+                other_job->driver->txn_commit(other_job);
+            }
+            assert(other_job->ret == 0);
+            other_job->cb(other_job->opaque, 0);
+            block_job_release(other_job->bs);
+        }
+    }
+}
+
 void block_job_completed(BlockJob *job, int ret)
 {
     BlockDriverState *bs = job->bs;
@@ -96,6 +159,10 @@ void block_job_completed(BlockJob *job, int ret)
         qemu_bh_delete(job->defer_to_main_loop_data.bh);
         job->defer_to_main_loop_data.bh = NULL;
     }
+    if (job->txn) {
+        block_job_completed_txn(job->txn, job, ret);
+        return;
+    }
     job->cb(job->opaque, ret);
     block_job_release(bs);
 }
@@ -384,3 +451,22 @@ void block_job_defer_to_main_loop(BlockJob *job,
 
     qemu_bh_schedule(data->bh);
 }
+
+BlockJobTxn *block_job_txn_new(void)
+{
+    BlockJobTxn *txn = g_new0(BlockJobTxn, 1);
+    QLIST_INIT(&txn->jobs);
+    return txn;
+}
+
+void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job)
+{
+    if (!txn) {
+        return;
+    }
+
+    assert(!job->txn);
+    job->txn = txn;
+
+    QLIST_INSERT_HEAD(&txn->jobs, job, txn_list);
+}
diff --git a/include/block/block.h b/include/block/block.h
index 7437590..c7fc5b6 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -13,6 +13,7 @@
 typedef struct BlockDriver BlockDriver;
 typedef struct BlockJob BlockJob;
 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 5bac2e2..d854ee0 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -157,6 +157,9 @@ struct BlockJob {
      */
     int ret;
 
+    /** Non-NULL if this job is part of a transaction */
+    BlockJobTxn *txn;
+    QLIST_ENTRY(BlockJob) txn_list;
 };
 
 /**
@@ -389,4 +392,27 @@ 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().
+ *
+ * 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_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 block job driver must call block_job_txn_prepare_to_complete() before
+ * final cleanup and completion.
+ */
+void block_job_txn_add_job(BlockJobTxn *txn, BlockJob *job);
+
 #endif
-- 
2.4.3