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>

block/block-backend.c

@@ -2096,3 +2096,13 @@ static void blk_root_drained_end(BdrvChild *child)
         }
     }
 }
+
+void blk_register_buf(BlockBackend *blk, void *host, size_t size)
+{
+    bdrv_register_buf(blk_bs(blk), host, size);
+}
+
+void blk_unregister_buf(BlockBackend *blk, void *host)
+{
+    bdrv_unregister_buf(blk_bs(blk), host);
+}

block/io.c

@@ -2825,3 +2825,27 @@ void bdrv_io_unplug(BlockDriverState *bs)
         bdrv_io_unplug(child->bs);
     }
 }
+
+void bdrv_register_buf(BlockDriverState *bs, void *host, size_t size)
+{
+    BdrvChild *child;
+
+    if (bs->drv && bs->drv->bdrv_register_buf) {
+        bs->drv->bdrv_register_buf(bs, host, size);
+    }
+    QLIST_FOREACH(child, &bs->children, next) {
+        bdrv_register_buf(child->bs, host, size);
+    }
+}
+
+void bdrv_unregister_buf(BlockDriverState *bs, void *host)
+{
+    BdrvChild *child;
+
+    if (bs->drv && bs->drv->bdrv_unregister_buf) {
+        bs->drv->bdrv_unregister_buf(bs, host);
+    }
+    QLIST_FOREACH(child, &bs->children, next) {
+        bdrv_unregister_buf(child->bs, host);
+    }
+}

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

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;
 };
 

include/sysemu/block-backend.h

@@ -229,4 +229,7 @@ void blk_io_limits_enable(BlockBackend *blk, const char *group);
 void blk_io_limits_update_group(BlockBackend *blk, const char *group);
 void blk_set_force_allow_inactivate(BlockBackend *blk);
 
+void blk_register_buf(BlockBackend *blk, void *host, size_t size);
+void blk_unregister_buf(BlockBackend *blk, void *host);
+
 #endif