block: Allow waiting for overlapping requests between begin/end

Previously, it was not possible to use wait_for_overlapping_requests()
between tracked_request_begin()/end() because it would wait for itself.

Ignore the current request in the overlap check and run more of the
bdrv_co_do_preadv/pwritev code with a BdrvTrackedRequest present.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>

block.c

@@ -2286,7 +2286,7 @@ static bool tracked_request_overlaps(BdrvTrackedRequest *req,
 }
 
 static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
-        int64_t offset, unsigned int bytes)
+        BdrvTrackedRequest *self, int64_t offset, unsigned int bytes)
 {
     BdrvTrackedRequest *req;
     int64_t cluster_offset;
@@ -2304,6 +2304,9 @@ static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
     do {
         retry = false;
         QLIST_FOREACH(req, &bs->tracked_requests, list) {
+            if (req == self) {
+                continue;
+            }
             if (tracked_request_overlaps(req, cluster_offset, cluster_bytes)) {
                 /* Hitting this means there was a reentrant request, for
                  * example, a block driver issuing nested requests.  This must
@@ -2906,10 +2909,10 @@ err:
  * implemented by the caller.
  */
 static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
-    int64_t offset, unsigned int bytes, QEMUIOVector *qiov, int flags)
+    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
+    QEMUIOVector *qiov, int flags)
 {
     BlockDriver *drv = bs->drv;
-    BdrvTrackedRequest req;
     int ret;
 
     int64_t sector_num = offset >> BDRV_SECTOR_BITS;
@@ -2924,11 +2927,9 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
     }
 
     if (bs->copy_on_read_in_flight) {
-        wait_for_overlapping_requests(bs, offset, bytes);
+        wait_for_overlapping_requests(bs, req, offset, bytes);
     }
 
-    tracked_request_begin(&req, bs, offset, bytes, false);
-
     if (flags & BDRV_REQ_COPY_ON_READ) {
         int pnum;
 
@@ -2975,8 +2976,6 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
     }
 
 out:
-    tracked_request_end(&req);
-
     if (flags & BDRV_REQ_COPY_ON_READ) {
         bs->copy_on_read_in_flight--;
     }
@@ -2992,6 +2991,8 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
     BdrvRequestFlags flags)
 {
     BlockDriver *drv = bs->drv;
+    BdrvTrackedRequest req;
+
     /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
     uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
     uint8_t *head_buf = NULL;
@@ -3042,9 +3043,11 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
         bytes = ROUND_UP(bytes, align);
     }
 
-    ret = bdrv_aligned_preadv(bs, offset, bytes,
+    tracked_request_begin(&req, bs, offset, bytes, false);
+    ret = bdrv_aligned_preadv(bs, &req, offset, bytes,
                               use_local_qiov ? &local_qiov : qiov,
                               flags);
+    tracked_request_end(&req);
 
     if (use_local_qiov) {
         qemu_iovec_destroy(&local_qiov);
@@ -3163,10 +3166,10 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
  * Forwards an already correctly aligned write request to the BlockDriver.
  */
 static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
-    int64_t offset, unsigned int bytes, QEMUIOVector *qiov, int flags)
+    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
+    QEMUIOVector *qiov, int flags)
 {
     BlockDriver *drv = bs->drv;
-    BdrvTrackedRequest req;
     int ret;
 
     int64_t sector_num = offset >> BDRV_SECTOR_BITS;
@@ -3176,12 +3179,10 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
     assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
 
     if (bs->copy_on_read_in_flight) {
-        wait_for_overlapping_requests(bs, offset, bytes);
+        wait_for_overlapping_requests(bs, req, offset, bytes);
     }
 
-    tracked_request_begin(&req, bs, offset, bytes, true);
+    ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);
-
-    ret = notifier_with_return_list_notify(&bs->before_write_notifiers, &req);
 
     if (ret < 0) {
         /* Do nothing, write notifier decided to fail this request */
@@ -3204,8 +3205,6 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
         bs->total_sectors = MAX(bs->total_sectors, sector_num + nb_sectors);
     }
 
-    tracked_request_end(&req);
-
     return ret;
 }
 
@@ -3216,6 +3215,7 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags)
 {
+    BdrvTrackedRequest req;
     int ret;
 
     if (!bs->drv) {
@@ -3234,7 +3234,9 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
         bdrv_io_limits_intercept(bs, bytes >> BDRV_SECTOR_BITS, true);
     }
 
-    ret = bdrv_aligned_pwritev(bs, offset, bytes, qiov, flags);
+    tracked_request_begin(&req, bs, offset, bytes, true);
+    ret = bdrv_aligned_pwritev(bs, &req, offset, bytes, qiov, flags);
+    tracked_request_end(&req);
 
     return ret;
 }