[PATCH v12 07/14] copy-on-read: limit COR operations to bottom node

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

Limit COR operations to the bottom node (inclusively) in the backing
chain when the bottom node name is given. It will be useful for a block
stream job when the COR-filter is applied. The bottom node is passed as
the base itself may change due to concurrent commit jobs on the same
backing chain.

Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
---
 block/copy-on-read.c | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 3d8e4db..8178a91 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -123,8 +123,46 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs,
                                            size_t qiov_offset,
                                            int flags)
 {
-    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
-                               flags | BDRV_REQ_COPY_ON_READ);
+    int64_t n = 0;
+    int local_flags;
+    int ret;
+    BDRVStateCOR *state = bs->opaque;
+
+    if (!state->bottom_bs) {
+        return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
+                                   flags | BDRV_REQ_COPY_ON_READ);
+    }
+
+    while (bytes) {
+        local_flags = flags;
+
+        /* In case of failure, try to copy-on-read anyway */
+        ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
+        if (!ret || ret < 0) {
+            ret = bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
+                                          state->bottom_bs, true, offset,
+                                          n, &n);
+            if (ret == 1 || ret < 0) {
+                local_flags |= BDRV_REQ_COPY_ON_READ;
+            }
+            /* Finish earlier if the end of a backing file has been reached */
+            if (ret == 0 && n == 0) {
+                break;
+            }
+        }
+
+        ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
+                                  local_flags);
+        if (ret < 0) {
+            return ret;
+        }
+
+        offset += n;
+        qiov_offset += n;
+        bytes -= n;
+    }
+
+    return 0;
 }
 
 
-- 
1.8.3.1