[Qemu-block] [PATCH v2 3/6] blockjob: add .start field

[John Snow]

Add an explicit start field to specify the entrypoint. We already have
ownership of the coroutine itself AND managing the lifetime of the
coroutine, let's take control of creation of the coroutine, too.

This will allow us to delay creation of the actual coroutine until we
know we'll actually start a BlockJob in block_job_start. This avoids
the sticky question of how to "un-create" a Coroutine that hasn't been
started yet.

Signed-off-by: John Snow <address@hidden>
---
 block/backup.c               | 23 ++++++++++++-----------
 block/commit.c               |  3 ++-
 block/mirror.c               |  4 +++-
 block/stream.c               |  3 ++-
 include/block/blockjob_int.h |  3 +++
 5 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index ed6d74a..622f64e 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -307,16 +307,6 @@ void backup_cow_request_end(CowRequest *req)
     cow_request_end(req);
 }
 
-static const BlockJobDriver backup_job_driver = {
-    .instance_size          = sizeof(BackupBlockJob),
-    .job_type               = BLOCK_JOB_TYPE_BACKUP,
-    .set_speed              = backup_set_speed,
-    .commit                 = backup_commit,
-    .abort                  = backup_abort,
-    .clean                  = backup_clean,
-    .attached_aio_context   = backup_attached_aio_context,
-};
-
 static BlockErrorAction backup_error_action(BackupBlockJob *job,
                                             bool read, int error)
 {
@@ -526,6 +516,17 @@ static void coroutine_fn backup_run(void *opaque)
     block_job_defer_to_main_loop(&job->common, backup_complete, data);
 }
 
+static const BlockJobDriver backup_job_driver = {
+    .instance_size          = sizeof(BackupBlockJob),
+    .job_type               = BLOCK_JOB_TYPE_BACKUP,
+    .start                  = backup_run,
+    .set_speed              = backup_set_speed,
+    .commit                 = backup_commit,
+    .abort                  = backup_abort,
+    .clean                  = backup_clean,
+    .attached_aio_context   = backup_attached_aio_context,
+};
+
 void backup_start(const char *job_id, BlockDriverState *bs,
                   BlockDriverState *target, int64_t speed,
                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
@@ -637,7 +638,7 @@ void backup_start(const char *job_id, BlockDriverState *bs,
 
     bdrv_op_block_all(target, job->common.blocker);
     job->common.len = len;
-    job->common.co = qemu_coroutine_create(backup_run, job);
+    job->common.co = qemu_coroutine_create(job->common.driver->start, job);
     block_job_txn_add_job(txn, &job->common);
     qemu_coroutine_enter(job->common.co);
     return;
diff --git a/block/commit.c b/block/commit.c
index d555600..cc2030d 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -205,6 +205,7 @@ static const BlockJobDriver commit_job_driver = {
     .instance_size = sizeof(CommitBlockJob),
     .job_type      = BLOCK_JOB_TYPE_COMMIT,
     .set_speed     = commit_set_speed,
+    .start         = commit_run,
 };
 
 void commit_start(const char *job_id, BlockDriverState *bs,
@@ -274,7 +275,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
     s->backing_file_str = g_strdup(backing_file_str);
 
     s->on_error = on_error;
-    s->common.co = qemu_coroutine_create(commit_run, s);
+    s->common.co = qemu_coroutine_create(s->common.driver->start, s);
 
     trace_commit_start(bs, base, top, s, s->common.co);
     qemu_coroutine_enter(s->common.co);
diff --git a/block/mirror.c b/block/mirror.c
index c81b5e0..3a29b94 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -891,6 +891,7 @@ static const BlockJobDriver mirror_job_driver = {
     .instance_size          = sizeof(MirrorBlockJob),
     .job_type               = BLOCK_JOB_TYPE_MIRROR,
     .set_speed              = mirror_set_speed,
+    .start                  = mirror_run,
     .complete               = mirror_complete,
     .pause                  = mirror_pause,
     .attached_aio_context   = mirror_attached_aio_context,
@@ -900,6 +901,7 @@ static const BlockJobDriver commit_active_job_driver = {
     .instance_size          = sizeof(MirrorBlockJob),
     .job_type               = BLOCK_JOB_TYPE_COMMIT,
     .set_speed              = mirror_set_speed,
+    .start                  = mirror_run,
     .complete               = mirror_complete,
     .pause                  = mirror_pause,
     .attached_aio_context   = mirror_attached_aio_context,
@@ -968,7 +970,7 @@ static void mirror_start_job(const char *job_id, 
BlockDriverState *bs,
 
     bdrv_op_block_all(target, s->common.blocker);
 
-    s->common.co = qemu_coroutine_create(mirror_run, s);
+    s->common.co = qemu_coroutine_create(s->common.driver->start, s);
     trace_mirror_start(bs, s, s->common.co, opaque);
     qemu_coroutine_enter(s->common.co);
 }
diff --git a/block/stream.c b/block/stream.c
index 906f7f3..8ffed9c 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -212,6 +212,7 @@ static const BlockJobDriver stream_job_driver = {
     .instance_size = sizeof(StreamBlockJob),
     .job_type      = BLOCK_JOB_TYPE_STREAM,
     .set_speed     = stream_set_speed,
+    .start         = stream_run,
 };
 
 void stream_start(const char *job_id, BlockDriverState *bs,
@@ -230,7 +231,7 @@ void stream_start(const char *job_id, BlockDriverState *bs,
     s->backing_file_str = g_strdup(backing_file_str);
 
     s->on_error = on_error;
-    s->common.co = qemu_coroutine_create(stream_run, s);
+    s->common.co = qemu_coroutine_create(s->common.driver->start, s);
     trace_stream_start(bs, base, s, s->common.co);
     qemu_coroutine_enter(s->common.co);
 }
diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
index 1c4bc90..ab21ae2 100644
--- a/include/block/blockjob_int.h
+++ b/include/block/blockjob_int.h
@@ -47,6 +47,9 @@ struct BlockJobDriver {
     /** Optional callback for job types that need to forward I/O status reset 
*/
     void (*iostatus_reset)(BlockJob *job);
 
+    /** Mandatory: Entrypoint for the Coroutine. */
+    CoroutineEntry *start;
+
     /**
      * Optional callback for job types whose completion must be triggered
      * manually.
-- 
2.7.4