Re: [Qemu-devel] [PATCH v5 04/42] block: Add child access functions

[Vladimir Sementsov-Ogievskiy]

13.06.2019 1:09, Max Reitz wrote:
> There are BDS children that the general block layer code can access,
> namely bs->file and bs->backing.  Since the introduction of filters and
> external data files, their meaning is not quite clear.  bs->backing can
> be a COW source, or it can be an R/W-filtered child; bs->file can be an
> R/W-filtered child, it can be data and metadata storage, or it can be
> just metadata storage.
> 
> This overloading really is not helpful.  This patch adds function that
> retrieve the correct child for each exact purpose.  Later patches in
> this series will make use of them.  Doing so will allow us to handle
> filter nodes and external data files in a meaningful way.
> 
> Signed-off-by: Max Reitz <address@hidden>

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

> ---
>   include/block/block_int.h | 57 ++++++++++++++++++++--
>   block.c                   | 99 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 153 insertions(+), 3 deletions(-)
> 
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 58fca37ba3..7ce71623f8 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h

[..]

>   
>   typedef struct BlockLimits {
> @@ -1249,4 +1258,46 @@ int coroutine_fn bdrv_co_copy_range_to(BdrvChild *src, 
> uint64_t src_offset,
>   
>   int refresh_total_sectors(BlockDriverState *bs, int64_t hint);
>   
> +BdrvChild *bdrv_filtered_cow_child(BlockDriverState *bs);
> +BdrvChild *bdrv_filtered_rw_child(BlockDriverState *bs);
> +BdrvChild *bdrv_filtered_child(BlockDriverState *bs);
> +BdrvChild *bdrv_metadata_child(BlockDriverState *bs);
> +BdrvChild *bdrv_storage_child(BlockDriverState *bs);
> +BdrvChild *bdrv_primary_child(BlockDriverState *bs);
> +

Wow! Such a big family :)

I'd like to put them into a table, just for me to make it easier to keep it all 
in mind.
But if you want, you may include it here as a comment.. But it's difficult to 
keep it less than 80 columns.
I think, I'll modify it after reviewing following patches.

+--------------------+----------------------------+-------------------------------+-------------------------------+
| child              | description                | filter node                 
  | format node                   |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| filtered_cow_child | for COW/COR                | NULL                        
  | bs->backing                   |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| filtered_rw_child  | for IO pass-through        | bs->backing or bs->file     
  | NULL                          |
|                    |                            | (only one may exist)        
  |                               |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| filtered_child     | one of the previous        |                             
  |                               |
|                    | for extended backing       | filtered_rw_child           
  | filtered_cow_child            |
|                    | chain                      |                             
  |                               |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| metadata_child     | where metadata is stored   | NULL                        
  | bs->file                      |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| storage_child      | where actual guest visible | 
bs->drv->bdrv_storage_child() | bs->drv->bdrv_storage_child() |
|                    | data is stored             | or filtered_rw_child        
  | or bs->file                   |
+--------------------+----------------------------+-------------------------------+-------------------------------+
| primary_child      | don't know yet             | filtered_rw_child           
  | bs->file                      |
+--------------------+----------------------------+-------------------------------+-------------------------------+




-- 
Best regards,
Vladimir