On 09/13/2013 04:25 AM, Peter Lieven wrote:
> this patch does 2 things:
> a) only do additional call outs if BDRV_BLOCK_ZERO is not already set.
> b) use bdi.discard_zeroes to return the zero state of an unallocated block.
> the callout to bdrv_has_zero_init() is only valid right after bdrv_create.
>
> Signed-off-by: Peter Lieven <p...@kamp.de>
> ---
> block.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 282943b..6698c10 100644
> --- a/block.c
> +++ b/block.c
> @@ -3153,8 +3153,10 @@ static int64_t coroutine_fn
> bdrv_co_get_block_status(BlockDriverState *bs,
> return ret;
> }
>
> - if (!(ret & BDRV_BLOCK_DATA)) {
> - if (bdrv_has_zero_init(bs)) {
> + if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {
Why not avoid the &&:
if ((ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) == 0) {
Then again, any decent compiler will probably already do that
optimization on your behalf.
> + BlockDriverInfo bdi;
> + if (bdrv_get_info(bs, &bdi) == 0 &&
> + bdi.discard_zeroes) {
> ret |= BDRV_BLOCK_ZERO;
> } else if (bs->backing_hd) {
> BlockDriverState *bs2 = bs->backing_hd;
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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