block: Convert block job core to BlockBackend

This adds a new BlockBackend field to the BlockJob struct, which
coexists with the BlockDriverState while converting the individual jobs.

When creating a block job, a new BlockBackend is created on top of the
given BlockDriverState, and it is destroyed when the BlockJob ends. The
reference to the BDS is now held by the BlockBackend instead of calling
bdrv_ref/unref manually.

We have to be careful when we use bdrv_replace_in_backing_chain() in
block jobs because this changes the BDS that job->blk points to. At the
moment block jobs are too tightly coupled with their BDS, so that moving
a job to another BDS isn't easily possible; therefore, we need to just
manually undo this change afterwards.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

3 files changed, 25 insertions, 18 deletions

diff --git a/block/mirror.c b/block/mirror.c
index b9986d8..efca8fc 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -478,6 +478,9 @@ static void mirror_exit(BlockJob *job, void *opaque)
             bdrv_reopen(s->target, bdrv_get_flags(to_replace), NULL);
         }
         bdrv_replace_in_backing_chain(to_replace, s->target);
+        /* We just changed the BDS the job BB refers to */
+        blk_remove_bs(job->blk);
+        blk_insert_bs(job->blk, src);
     }
 
 out:
diff --git a/blockjob.c b/blockjob.c
index e916b41..2097e1d 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -64,13 +64,17 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
                        int64_t speed, BlockCompletionFunc *cb,
                        void *opaque, Error **errp)
 {
+    BlockBackend *blk;
     BlockJob *job;
 
     if (bs->job) {
         error_setg(errp, QERR_DEVICE_IN_USE, bdrv_get_device_name(bs));
         return NULL;
     }
-    bdrv_ref(bs);
+
+    blk = blk_new();
+    blk_insert_bs(blk, bs);
+
     job = g_malloc0(driver->instance_size);
     error_setg(&job->blocker, "block device is in use by block job: %s",
                BlockJobType_lookup[driver->job_type]);
@@ -80,6 +84,7 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
     job->driver        = driver;
     job->id            = g_strdup(bdrv_get_device_name(bs));
     job->bs            = bs;
+    job->blk           = blk;
     job->cb            = cb;
     job->opaque        = opaque;
     job->busy          = true;
@@ -110,9 +115,10 @@ void block_job_ref(BlockJob *job)
 void block_job_unref(BlockJob *job)
 {
     if (--job->refcnt == 0) {
-        job->bs->job = NULL;
-        bdrv_op_unblock_all(job->bs, job->blocker);
-        bdrv_unref(job->bs);
+        BlockDriverState *bs = blk_bs(job->blk);
+        bs->job = NULL;
+        bdrv_op_unblock_all(bs, job->blocker);
+        blk_unref(job->blk);
         error_free(job->blocker);
         g_free(job->id);
         QLIST_REMOVE(job, job_list);
@@ -153,7 +159,7 @@ static void block_job_completed_txn_abort(BlockJob *job)
     txn->aborting = true;
     /* We are the first failed job. Cancel other jobs. */
     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
-        ctx = bdrv_get_aio_context(other_job->bs);
+        ctx = blk_get_aio_context(other_job->blk);
         aio_context_acquire(ctx);
     }
     QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
@@ -170,7 +176,7 @@ static void block_job_completed_txn_abort(BlockJob *job)
         assert(other_job->completed);
     }
     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
-        ctx = bdrv_get_aio_context(other_job->bs);
+        ctx = blk_get_aio_context(other_job->blk);
         block_job_completed_single(other_job);
         aio_context_release(ctx);
     }
@@ -192,7 +198,7 @@ static void block_job_completed_txn_success(BlockJob *job)
     }
     /* We are the last completed job, commit the transaction. */
     QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
-        ctx = bdrv_get_aio_context(other_job->bs);
+        ctx = blk_get_aio_context(other_job->blk);
         aio_context_acquire(ctx);
         assert(other_job->ret == 0);
         block_job_completed_single(other_job);
@@ -202,9 +208,7 @@ static void block_job_completed_txn_success(BlockJob *job)
 
 void block_job_completed(BlockJob *job, int ret)
 {
-    BlockDriverState *bs = job->bs;
-
-    assert(bs->job == job);
+    assert(blk_bs(job->blk)->job == job);
     assert(!job->completed);
     job->completed = true;
     job->ret = ret;
@@ -295,11 +299,10 @@ static int block_job_finish_sync(BlockJob *job,
                                  void (*finish)(BlockJob *, Error **errp),
                                  Error **errp)
 {
-    BlockDriverState *bs = job->bs;
     Error *local_err = NULL;
     int ret;
 
-    assert(bs->job == job);
+    assert(blk_bs(job->blk)->job == job);
 
     block_job_ref(job);
     finish(job, &local_err);
@@ -310,7 +313,7 @@ static int block_job_finish_sync(BlockJob *job,
     }
     while (!job->completed) {
         aio_poll(job->deferred_to_main_loop ? qemu_get_aio_context() :
-                                              bdrv_get_aio_context(bs),
+                                              blk_get_aio_context(job->blk),
                  true);
     }
     ret = (job->cancelled && job->ret == 0) ? -ECANCELED : job->ret;
@@ -337,7 +340,7 @@ void block_job_cancel_sync_all(void)
     AioContext *aio_context;
 
     while ((job = QLIST_FIRST(&block_jobs))) {
-        aio_context = bdrv_get_aio_context(job->bs);
+        aio_context = blk_get_aio_context(job->blk);
         aio_context_acquire(aio_context);
         block_job_cancel_sync(job);
         aio_context_release(aio_context);
@@ -362,7 +365,7 @@ void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns)
     if (block_job_is_paused(job)) {
         qemu_coroutine_yield();
     } else {
-        co_aio_sleep_ns(bdrv_get_aio_context(job->bs), type, ns);
+        co_aio_sleep_ns(blk_get_aio_context(job->blk), type, ns);
     }
     job->busy = true;
 }
@@ -491,7 +494,7 @@ static void block_job_defer_to_main_loop_bh(void *opaque)
     aio_context_acquire(data->aio_context);
 
     /* Fetch BDS AioContext again, in case it has changed */
-    aio_context = bdrv_get_aio_context(data->job->bs);
+    aio_context = blk_get_aio_context(data->job->blk);
     aio_context_acquire(aio_context);
 
     data->job->deferred_to_main_loop = false;
@@ -511,7 +514,7 @@ void block_job_defer_to_main_loop(BlockJob *job,
     BlockJobDeferToMainLoopData *data = g_malloc(sizeof(*data));
     data->job = job;
     data->bh = qemu_bh_new(block_job_defer_to_main_loop_bh, data);
-    data->aio_context = bdrv_get_aio_context(job->bs);
+    data->aio_context = blk_get_aio_context(job->blk);
     data->fn = fn;
     data->opaque = opaque;
     job->deferred_to_main_loop = true;
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index 4ac6831..32012af 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -82,7 +82,8 @@ struct BlockJob {
     const BlockJobDriver *driver;
 
     /** The block device on which the job is operating.  */
-    BlockDriverState *bs;
+    BlockDriverState *bs; /* TODO Remove */
+    BlockBackend *blk;
 
     /**
      * The ID of the block job. Currently the BlockBackend name of the BDS