Re: [Qemu-devel] [PATCHv4 4/4] block: avoid creating oversized writes in multiwrite_merge

[Max Reitz <mreitz@redhat.com>]

On 2014-10-16 at 09:54, Peter Lieven wrote:
> Signed-off-by: Peter Lieven <pl@kamp.de>
> Reviewed-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
> ---
>   block.c |    5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/block.c b/block.c
> index 0fbf916..9ad2287 100644
> --- a/block.c
> +++ b/block.c
> @@ -4554,6 +4554,11 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
>               merge = 0;
>           }
>   
> +        if (bs->bl.max_transfer_length && reqs[outidx].nb_sectors +
> +            reqs[i].nb_sectors > bs->bl.max_transfer_length) {
> +            merge = 0;
> +        }
> +
>           if (merge) {
>               size_t size;
>               QEMUIOVector *qiov = g_malloc0(sizeof(*qiov));

Reviewed-by: Max Reitz <mreitz@redhat.com>

I feel like we should respect max_transfer_length in more than just this 
function, though. Every block device (or block driver) that sets a 
maximum transfer length should check requests against it as well, so we 
don't need to duplicate the same tests in the block layer functions, but 
maybe if at some point there are no things left to be done on the block 
layer, we could do that.

Max