From: Vladimir Sementsov-Ogievskiy <etendren@gmail.com>

Introduce lock/unlock range functionality, based on serialized
requests. This is needed to refactor backup, dropping local
tracked-request-like synchronization.

Signed-off-by: Vladimir Sementsov-Ogievskiy <etendren@gmail.com>
---
 include/block/block_int.h |  3 +++
 block/io.c                | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 92ecbd866e..20617e5853 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -856,6 +856,9 @@ int coroutine_fn bdrv_co_preadv(BdrvChild *child,
 int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
+void *coroutine_fn bdrv_co_try_lock(BdrvChild *child,
+                                    int64_t offset, unsigned int bytes);
+void coroutine_fn bdrv_co_unlock(void *opaque);
 
 extern unsigned int bdrv_drain_all_count;
 void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent);
diff --git a/block/io.c b/block/io.c
index d4e46cb3dc..fd4ec53167 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3243,3 +3243,38 @@ int bdrv_truncate(BdrvChild *child, int64_t offset, PreallocMode prealloc,
 
     return tco.ret;
 }
+
+void *coroutine_fn bdrv_co_try_lock(BdrvChild *child,
+                                    int64_t offset, unsigned int bytes)
+{
+    BlockDriverState *bs = child->bs;
+    BdrvTrackedRequest *req;
+
+    qemu_co_mutex_lock(&bs->reqs_lock);
+
+    QLIST_FOREACH(req, &bs->tracked_requests, list) {
+        if (req->type == BDRV_TRACKED_READ) {
+            continue;
+        }
+        if (tracked_request_overlaps(req, offset, bytes)) {
+            qemu_co_mutex_unlock(&bs->reqs_lock);
+            return NULL;
+        }
+    }
+
+    qemu_co_mutex_unlock(&bs->reqs_lock);
+
+    req = g_new(BdrvTrackedRequest, 1);
+    tracked_request_begin(req, bs, offset, bytes, BDRV_TRACKED_READ);
+    mark_request_serialising(req, bdrv_get_cluster_size(bs));
+
+    return req;
+}
+
+void coroutine_fn bdrv_co_unlock(void *opaque)
+{
+    BdrvTrackedRequest *req = opaque;
+
+    tracked_request_end(req);
+    g_free(req);
+}
-- 
2.18.0