[PATCH v9 6/9] copy-on-read: skip non-guest reads if no copy needed

[Andrey Shinkevich]

If the flag BDRV_REQ_PREFETCH was set, pass it further to the
COR-driver to skip unneeded reading. 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 | 14 ++++++++++----
 block/io.c           |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index f53f7e0..5389dca 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -145,10 +145,16 @@ 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;
+        if ((flags & BDRV_REQ_PREFETCH) &
+            !(local_flags & BDRV_REQ_COPY_ON_READ)) {
+            /* Skip non-guest reads if no copy needed */
+        } else {
+
+            ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
+                                      local_flags);
+            if (ret < 0) {
+                return ret;
+            }
         }
 
         offset += n;
diff --git a/block/io.c b/block/io.c
index 11df188..62b75a5 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1388,7 +1388,7 @@ static int coroutine_fn 
bdrv_co_do_copy_on_readv(BdrvChild *child,
             qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
 
             ret = bdrv_driver_preadv(bs, cluster_offset, pnum,
-                                     &local_qiov, 0, 0);
+                                     &local_qiov, 0, flags & 
BDRV_REQ_PREFETCH);
             if (ret < 0) {
                 goto err;
             }
-- 
1.8.3.1