block: Introduce buf register API

Allow block driver to map and unmap a buffer for later I/O, as a performance
hint.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20180116060901.17413-5-famz@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>

2 files changed, 19 insertions, 1 deletions

diff --git a/include/block/block.h b/include/block/block.h
index 9b12774ddf..2025d7ed19 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -631,5 +631,14 @@ void bdrv_del_child(BlockDriverState *parent, BdrvChild *child, Error **errp);
 
 bool bdrv_can_store_new_dirty_bitmap(BlockDriverState *bs, const char *name,
                                      uint32_t granularity, Error **errp);
-
+/**
+ *
+ * bdrv_register_buf/bdrv_unregister_buf:
+ *
+ * Register/unregister a buffer for I/O. For example, VFIO drivers are
+ * interested to know the memory areas that would later be used for I/O, so
+ * that they can prepare IOMMU mapping etc., to get better performance.
+ */
+void bdrv_register_buf(BlockDriverState *bs, void *host, size_t size);
+void bdrv_unregister_buf(BlockDriverState *bs, void *host);
 #endif
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 29cafa4236..99b9190627 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -446,6 +446,15 @@ struct BlockDriver {
                                                 const char *name,
                                                 Error **errp);
 
+    /**
+     * Register/unregister a buffer for I/O. For example, when the driver is
+     * interested to know the memory areas that will later be used in iovs, so
+     * that it can do IOMMU mapping with VFIO etc., in order to get better
+     * performance. In the case of VFIO drivers, this callback is used to do
+     * DMA mapping for hot buffers.
+     */
+    void (*bdrv_register_buf)(BlockDriverState *bs, void *host, size_t size);
+    void (*bdrv_unregister_buf)(BlockDriverState *bs, void *host);
     QLIST_ENTRY(BlockDriver) list;
 };