job: Create Job, JobDriver and job_create()

This is the first step towards creating an infrastructure for generic
background jobs that aren't tied to a block device. For now, Job only
stores its ID and JobDriver, the rest stays in BlockJob.

The following patches will move over more parts of BlockJob to Job if
they are meaningful outside the context of a block job.

BlockJob.driver is now redundant, but this patch leaves it around to
avoid unnecessary churn. The next patches will get rid of almost all of
its uses anyway so that it can be removed later with much less churn.

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

include/block/blockjob.h

@@ -26,6 +26,7 @@
 #ifndef BLOCKJOB_H
 #define BLOCKJOB_H
 
+#include "qemu/job.h"
 #include "block/block.h"
 #include "qemu/ratelimit.h"
 
@@ -40,17 +41,15 @@ typedef struct BlockJobTxn BlockJobTxn;
  * Long-running operation on a BlockDriverState.
  */
 typedef struct BlockJob {
+    /** Data belonging to the generic Job infrastructure */
+    Job job;
+
     /** The job type, including the job vtable.  */
     const BlockJobDriver *driver;
 
     /** The block device on which the job is operating.  */
     BlockBackend *blk;
 
-    /**
-     * The ID of the block job. May be NULL for internal jobs.
-     */
-    char *id;
-
     /**
      * The coroutine that executes the job.  If not NULL, it is
      * reentered when busy is false and the job is cancelled.

include/block/blockjob_int.h

@@ -35,8 +35,8 @@
  * A class type for block job driver.
  */
 struct BlockJobDriver {
-    /** Derived BlockJob struct size */
-    size_t instance_size;
+    /** Generic JobDriver callbacks and settings */
+    JobDriver job_driver;
 
     /** String describing the operation, part of query-block-jobs QMP API */
     BlockJobType job_type;