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.
Add the BDRV_REQ_PREFETCH flag to the supported_read_flags of the
COR-filter.
block: Modify the comment for the flag BDRV_REQ_PREFETCH as we are
going to use it alone and pass it to the COR-filter driver for further
processing.
Signed-off-by: Andrey Shinkevich
---
block/copy-on-read.c | 14 ++
include/block/block.h | 8 +---
2 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 2cddc96..123d197 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -49,6 +49,8 @@ static int cor_open(BlockDriverState *bs, QDict *options, int
flags,
return -EINVAL;
}
+bs->supported_read_flags = BDRV_REQ_PREFETCH;
+
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
@@ -150,10 +152,14 @@ 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;
diff --git a/include/block/block.h b/include/block/block.h
index 81a3894..3499554 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -81,9 +81,11 @@ typedef enum {
BDRV_REQ_NO_FALLBACK= 0x100,
/*
- * BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_READ
- * on read request and means that caller doesn't really need data to be
- * written to qiov parameter which may be NULL.
+ * BDRV_REQ_PREFETCH makes sense only in the context of copy-on-read
+ * (i.e., together with the BDRV_REQ_COPY_ON_READ flag or when a COR
+ * filter is involved), in which case it signals that the COR operation
+ * need not read the data into memory (qiov) but only ensure they are
+ * copied to the top layer (i.e., that COR operation is done).
*/
BDRV_REQ_PREFETCH = 0x200,
/* Mask of valid flags */
--
1.8.3.1
