Re: [Qemu-block] [PATCH v2 12/14] qemu-img: Make MapEntry a QAPI struct

[Paolo Bonzini]

On 25/11/2015 08:39, Fam Zheng wrote:
>           */
> -        if (next &&
> -            (next->flags & (BDRV_BLOCK_DATA|BDRV_BLOCK_ZERO)) != 
> BDRV_BLOCK_DATA) {
> -            next->flags &= ~BDRV_BLOCK_DATA;
> -            next->flags |= BDRV_BLOCK_ZERO;
> +        if (next && !next->data) {
> +            next->zero = true;

                before          after
0               ZERO            ZERO
DATA            DATA            DATA
DATA|ZERO       ZERO            DATA|ZERO
ZERO            ZERO            ZERO

This would not coalesce 0 with DATA|ZERO.

I think you need to do exactly as in the older code: test (!next->data
|| next->zero), and clear next->data.

Paolo