[pve-devel] [RFC qemu 1/2] PVE: Add sequential job transaction support

[Stefan Reiter <s.reiter@proxmox.com>]

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
 include/qemu/job.h | 12 ++++++++++++
 job.c              | 24 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 32aabb1c60..f7a6a0926a 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -280,6 +280,18 @@ typedef enum JobCreateFlags {
  */
 JobTxn *job_txn_new(void);
 
+/**
+ * Create a new transaction and set it to sequential mode, i.e. run all jobs
+ * one after the other instead of at the same time.
+ */
+JobTxn *job_txn_new_seq(void);
+
+/**
+ * Helper method to start the first job in a sequential transaction to kick it
+ * off. Other jobs will be run after this one completes.
+ */
+void job_txn_start_seq(JobTxn *txn);
+
 /**
  * Release a reference that was previously acquired with job_txn_add_job or
  * job_txn_new. If it's the last reference to the object, it will be freed.
diff --git a/job.c b/job.c
index bcbbb0be02..901f84dceb 100644
--- a/job.c
+++ b/job.c
@@ -72,6 +72,8 @@ struct JobTxn {
 
     /* Reference count */
     int refcnt;
+
+    bool sequential;
 };
 
 /* Right now, this mutex is only needed to synchronize accesses to job->busy
@@ -102,6 +104,25 @@ JobTxn *job_txn_new(void)
     return txn;
 }
 
+JobTxn *job_txn_new_seq(void)
+{
+    JobTxn *txn = job_txn_new();
+    txn->sequential = true;
+    return txn;
+}
+
+void job_txn_start_seq(JobTxn *txn)
+{
+    assert(txn->sequential);
+    assert(!txn->aborting);
+
+    Job *first = QLIST_FIRST(&txn->jobs);
+    assert(first);
+    assert(first->status == JOB_STATUS_CREATED);
+
+    job_start(first);
+}
+
 static void job_txn_ref(JobTxn *txn)
 {
     txn->refcnt++;
@@ -841,6 +862,9 @@ static void job_completed_txn_success(Job *job)
      */
     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
         if (!job_is_completed(other_job)) {
+            if (txn->sequential) {
+                job_start(other_job);
+            }
             return;
         }
         assert(other_job->ret == 0);
-- 
2.20.1