[PATCH v13 13/15] block: add lock/unlock range functions

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.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 <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 include/block/block_int.h |  4 ++++
 block/io.c                | 44 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 0422acdf1c..b59011ca97 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -65,6 +65,7 @@ enum BdrvTrackedRequestType {
     BDRV_TRACKED_WRITE,
     BDRV_TRACKED_DISCARD,
     BDRV_TRACKED_TRUNCATE,
+    BDRV_TRACKED_LOCK,
 };
 
 typedef struct BdrvTrackedRequest {
@@ -968,6 +969,9 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
 int coroutine_fn bdrv_co_pwritev_part(BdrvChild *child,
     int64_t offset, unsigned int bytes,
     QEMUIOVector *qiov, size_t qiov_offset, BdrvRequestFlags flags);
+void *coroutine_fn bdrv_co_try_lock(BlockDriverState *bs,
+                                    int64_t offset, unsigned int bytes);
+void coroutine_fn bdrv_co_unlock(void *opaque);
 
 static inline int coroutine_fn bdrv_co_pread(BdrvChild *child,
     int64_t offset, unsigned int bytes, void *buf, BdrvRequestFlags flags)
diff --git a/block/io.c b/block/io.c
index f5f7b7357c..a749583453 100644
--- a/block/io.c
+++ b/block/io.c
@@ -786,6 +786,15 @@ void bdrv_dec_in_flight(BlockDriverState *bs)
     bdrv_wakeup(bs);
 }
 
+static bool ignore_intersection(BdrvTrackedRequest *a, BdrvTrackedRequest *b)
+{
+    return a == b || (!a->serialising && !b->serialising) ||
+        (a->type == BDRV_TRACKED_LOCK && b->type == BDRV_TRACKED_READ &&
+         !b->serialising) ||
+        (b->type == BDRV_TRACKED_LOCK && a->type == BDRV_TRACKED_READ &&
+         !a->serialising);
+}
+
 static bool coroutine_fn do_wait_serialising_requests(BdrvTrackedRequest *self,
                                                       bool wait)
 {
@@ -802,7 +811,7 @@ static bool coroutine_fn do_wait_serialising_requests(BdrvTrackedRequest *self,
         retry = false;
         qemu_co_mutex_lock(&bs->reqs_lock);
         QLIST_FOREACH(req, &bs->tracked_requests, list) {
-            if (req == self || (!req->serialising && !self->serialising)) {
+            if (ignore_intersection(self, req)) {
                 continue;
             }
             if (tracked_request_overlaps(req, self->overlap_offset,
@@ -840,6 +849,12 @@ static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
     return do_wait_serialising_requests(self, true);
 }
 
+static bool coroutine_fn should_wait_serialising_requests(
+        BdrvTrackedRequest *self)
+{
+    return do_wait_serialising_requests(self, false);
+}
+
 static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
                                    size_t size)
 {
@@ -3378,3 +3393,30 @@ int bdrv_truncate(BdrvChild *child, int64_t offset, PreallocMode prealloc,
 
     return tco.ret;
 }
+
+void *coroutine_fn bdrv_co_try_lock(BlockDriverState *bs,
+                                    int64_t offset, unsigned int bytes)
+{
+    BdrvTrackedRequest *req = g_new(BdrvTrackedRequest, 1);
+
+    tracked_request_begin(req, bs, offset, bytes, BDRV_TRACKED_LOCK);
+    mark_request_serialising(req, bdrv_get_cluster_size(bs));
+
+    if (should_wait_serialising_requests(req)) {
+        tracked_request_end(req);
+        g_free(req);
+        return NULL;
+    }
+
+    return req;
+}
+
+void coroutine_fn bdrv_co_unlock(void *opaque)
+{
+    BdrvTrackedRequest *req = opaque;
+
+    assert(req->type == BDRV_TRACKED_LOCK);
+
+    tracked_request_end(req);
+    g_free(req);
+}
-- 
2.21.0