[PATCH v12 12/14] copy-on-read: skip non-guest reads if no copy needed

[Andrey Shinkevich via <qemu-devel@nongnu.org>]

If the flag BDRV_REQ_PREFETCH was set, skip idling read/write
operations in COR-driver. It can be taken into account for the
COR-algorithms optimization. That check is being made during the
block stream job by the moment.

Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
---
 block/copy-on-read.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index a2b180a..081e661 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -153,10 +153,14 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
             }
         }
 
-        ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
-                                  local_flags);
-        if (ret < 0) {
-            return ret;
+        /* Skip if neither read nor write are needed */
+        if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=
+            BDRV_REQ_PREFETCH) {
+            ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
+                                      local_flags);
+            if (ret < 0) {
+                return ret;
+            }
         }
 
         offset += n;
-- 
1.8.3.1