Re: [Qemu-devel] [PATCH v6 16/42] block: Flush all children in generic code

[Vladimir Sementsov-Ogievskiy]

09.08.2019 19:13, Max Reitz wrote:
> If the driver does not support .bdrv_co_flush() so bdrv_co_flush()
> itself has to flush the children of the given node, it should not flush
> just bs->file->bs, but in fact all children.
> 
> In any case, the BLKDBG_EVENT() should be emitted on the primary child,
> because that is where a blkdebug node would be if there is any.
> 
> Suggested-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Signed-off-by: Max Reitz <address@hidden>
> ---
>   block/io.c | 23 +++++++++++++++++------
>   1 file changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index c5a8e3e6a3..bcc770d336 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2572,6 +2572,8 @@ static void coroutine_fn bdrv_flush_co_entry(void 
> *opaque)
>   
>   int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>   {
> +    BdrvChild *primary_child = bdrv_primary_child(bs);
> +    BdrvChild *child;
>       int current_gen;
>       int ret = 0;
>   
> @@ -2601,7 +2603,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>       }
>   
>       /* Write back cached data to the OS even with cache=unsafe */
> -    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_OS);
> +    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_OS);
>       if (bs->drv->bdrv_co_flush_to_os) {
>           ret = bs->drv->bdrv_co_flush_to_os(bs);
>           if (ret < 0) {
> @@ -2611,15 +2613,15 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>   
>       /* But don't actually force it to the disk with cache=unsafe */
>       if (bs->open_flags & BDRV_O_NO_FLUSH) {
> -        goto flush_parent;
> +        goto flush_children;
>       }
>   
>       /* Check if we really need to flush anything */
>       if (bs->flushed_gen == current_gen) {
> -        goto flush_parent;
> +        goto flush_children;
>       }
>   
> -    BLKDBG_EVENT(bs->file, BLKDBG_FLUSH_TO_DISK);
> +    BLKDBG_EVENT(primary_child, BLKDBG_FLUSH_TO_DISK);
>       if (!bs->drv) {
>           /* bs->drv->bdrv_co_flush() might have ejected the BDS
>            * (even in case of apparent success) */
> @@ -2663,8 +2665,17 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>       /* Now flush the underlying protocol.  It will also have BDRV_O_NO_FLUSH
>        * in the case of cache=unsafe, so there are no useless flushes.
>        */
> -flush_parent:
> -    ret = bs->file ? bdrv_co_flush(bs->file->bs) : 0;
> +flush_children:
> +    ret = 0; > +    QLIST_FOREACH(child, &bs->children, next) {
> +        int this_child_ret;
> +
> +        this_child_ret = bdrv_co_flush(child->bs);
> +        if (!ret) {
> +            ret = this_child_ret;
> +        }
> +    }

Hmm, you said that we want to flush only children with write-access from 
parent..
Shouldn't we check it? Or we assume that it's always safe to call bdrv_co_flush 
on
a node?

> +
>   out:
>       /* Notify any pending flushes that we have completed */
>       if (ret == 0) {
> 


-- 
Best regards,
Vladimir