[Qemu-devel] [PATCH 1/8] block: add bdrv_aio_stream

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

From: Anthony Liguori <aliguori@us.ibm.com>

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
 block.c     |   32 ++++++++++++++++++++++++++++++++
 block.h     |    2 ++
 block_int.h |    3 +++
 3 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index f731c7a..5e3476c 100644
--- a/block.c
+++ b/block.c
@@ -2248,6 +2248,38 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
     return ret;
 }
 
+/**
+ * Attempt to stream an image starting from sector_num.
+ *
+ * @sector_num - the first sector to start streaming from
+ * @cb - block completion callback
+ * @opaque - data to pass completion callback
+ *
+ * Returns NULL if the image format not support streaming, the image is
+ * read-only, or no image is open.
+ *
+ * The intention of this function is for a user to execute it once with a
+ * sector_num of 0 and then upon receiving a completion callback, to remember
+ * the number of sectors "streamed", and then to call this function again with
+ * an offset adjusted by the number of sectors previously streamed.
+ *
+ * This allows a user to progressive stream in an image at a pace that makes
+ * sense.  In general, this function tries to do the smallest amount of I/O
+ * possible to do some useful work.
+ *
+ * This function only really makes sense in combination with a block format
+ * that supports copy on read and has it enabled.  If copy on read is not
+ * enabled, a block format driver may return NULL.
+ */
+BlockDriverAIOCB *bdrv_aio_stream(BlockDriverState *bs, int64_t sector_num,
+                                  BlockDriverCompletionFunc *cb, void *opaque)
+{
+    if (!bs->drv || bs->read_only || !bs->drv->bdrv_aio_stream) {
+        return NULL;
+    }
+
+    return bs->drv->bdrv_aio_stream(bs, sector_num, cb, opaque);
+}
 
 typedef struct MultiwriteCB {
     int error;
diff --git a/block.h b/block.h
index 52e9cad..fad828a 100644
--- a/block.h
+++ b/block.h
@@ -119,6 +119,8 @@ BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
                                   BlockDriverCompletionFunc *cb, void *opaque);
 BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
 				 BlockDriverCompletionFunc *cb, void *opaque);
+BlockDriverAIOCB *bdrv_aio_stream(BlockDriverState *bs, int64_t sector_num,
+                                  BlockDriverCompletionFunc *cb, void *opaque);
 void bdrv_aio_cancel(BlockDriverAIOCB *acb);
 
 typedef struct BlockRequest {
diff --git a/block_int.h b/block_int.h
index 545ad11..0c125d0 100644
--- a/block_int.h
+++ b/block_int.h
@@ -73,6 +73,9 @@ struct BlockDriver {
         BlockDriverCompletionFunc *cb, void *opaque);
     BlockDriverAIOCB *(*bdrv_aio_flush)(BlockDriverState *bs,
         BlockDriverCompletionFunc *cb, void *opaque);
+    BlockDriverAIOCB *(*bdrv_aio_stream)(BlockDriverState *bs,
+        int64_t sector_num,
+        BlockDriverCompletionFunc *cb, void *opaque);
     int (*bdrv_discard)(BlockDriverState *bs, int64_t sector_num,
                         int nb_sectors);
 
-- 
1.7.4.4