block: remove unused BLOCK_OP_TYPE_DATAPLANE

BLOCK_OP_TYPE_DATAPLANE prevents BlockDriverState from being used by
virtio-blk/virtio-scsi with IOThread. Commit b112a65c52aa ("block:
declare blockjobs and dataplane friends!") eliminated the main reason
for this blocker in 2014.

Nowadays the block layer supports I/O from multiple AioContexts, so
there is even less reason to block IOThread users. Any legitimate
reasons related to interference would probably also apply to
non-IOThread users.

The only remaining users are bdrv_op_unblock(BLOCK_OP_TYPE_DATAPLANE)
calls after bdrv_op_block_all(). If we remove BLOCK_OP_TYPE_DATAPLANE
their behavior doesn't change.

Existing bdrv_op_block_all() callers that don't explicitly unblock
BLOCK_OP_TYPE_DATAPLANE seem to do so simply because no one bothered to
rather than because it is necessary to keep BLOCK_OP_TYPE_DATAPLANE
blocked.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250203182529.269066-1-stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/replication.c

@@ -576,7 +576,6 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
             return;
         }
         bdrv_op_block_all(top_bs, s->blocker);
-        bdrv_op_unblock(top_bs, BLOCK_OP_TYPE_DATAPLANE, s->blocker);
 
         bdrv_graph_wrunlock();
 

blockjob.c

@@ -539,8 +539,6 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
         goto fail;
     }
 
-    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
-
     if (!block_job_set_speed(job, speed, errp)) {
         goto fail;
     }

hw/block/virtio-blk.c

@@ -1562,15 +1562,6 @@ static bool virtio_blk_vq_aio_context_init(VirtIOBlock *s, Error **errp)
             error_setg(errp, "ioeventfd is required for iothread");
             return false;
         }
-
-        /*
-         * If ioeventfd is (re-)enabled while the guest is running there could
-         * be block jobs that can conflict.
-         */
-        if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
-            error_prepend(errp, "cannot start virtio-blk ioeventfd: ");
-            return false;
-        }
     }
 
     s->vq_aio_context = g_new(AioContext *, conf->num_queues);

hw/scsi/virtio-scsi.c

@@ -1065,9 +1065,6 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
     int ret;
 
     if (s->ctx && !s->dataplane_fenced) {
-        if (blk_op_is_blocked(sd->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
-            return;
-        }
         ret = blk_set_aio_context(sd->conf.blk, s->ctx, errp);
         if (ret < 0) {
             return;

include/block/block-common.h

@@ -356,7 +356,6 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_CHANGE,
     BLOCK_OP_TYPE_COMMIT_SOURCE,
     BLOCK_OP_TYPE_COMMIT_TARGET,
-    BLOCK_OP_TYPE_DATAPLANE,
     BLOCK_OP_TYPE_DRIVE_DEL,
     BLOCK_OP_TYPE_EJECT,
     BLOCK_OP_TYPE_EXTERNAL_SNAPSHOT,