blockjobs: add prepare callback

Some jobs upon finalization may need to perform some work that can
still fail. If these jobs are part of a transaction, it's important
that these callbacks fail the entire transaction.

We allow for a new callback in addition to commit/abort/clean that
allows us the opportunity to have fairly late-breaking failures
in the transactional process.

The expected flow is:

- All jobs in a transaction converge to the PENDING state,
  added in a forthcoming commit.
- Upon being finalized, either automatically or explicitly
  by the user, jobs prepare to complete.
- If any job fails preparation, all jobs call .abort.
- Otherwise, they succeed and call .commit.

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

1 files changed, 10 insertions, 0 deletions

diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
index 259d49b32a..642adce68b 100644
--- a/include/block/blockjob_int.h
+++ b/include/block/blockjob_int.h
@@ -54,6 +54,16 @@ struct BlockJobDriver {
     void (*complete)(BlockJob *job, Error **errp);
 
     /**
+     * If the callback is not NULL, prepare will be invoked when all the jobs
+     * belonging to the same transaction complete; or upon this job's completion
+     * if it is not in a transaction.
+     *
+     * This callback will not be invoked if the job has already failed.
+     * If it fails, abort and then clean will be called.
+     */
+    int (*prepare)(BlockJob *job);
+
+    /**
      * If the callback is not NULL, it will be invoked when all the jobs
      * belonging to the same transaction complete; or upon this job's
      * completion if it is not in a transaction. Skipped if NULL.