On Fri, Sep 09, 2016 at 03:31:47PM +0300, Denis V. Lunev wrote:
> They should work very similar, covering same areas if backing store is
> shorter than the image. This change is necessary for the followup patch
> switching to bdrv_get_block_status_above() in mirror to avoid assert
> in check_block.
I wonder why bdrv_is_allocated_above has to be a separate function
rather than a trivial wrapper around bdrv_get_block_status_above() (like
bdrv_is_allocated() is over bdrv_get_block_status())?
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> CC: Stefan Hajnoczi <stefa...@redhat.com>
> CC: Fam Zheng <f...@redhat.com>
> CC: Kevin Wolf <kw...@redhat.com>
> CC: Max Reitz <mre...@redhat.com>
> CC: Jeff Cody <jc...@redhat.com>
> ---
> block/io.c | 26 ++++++++++++++++++++------
> 1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/block/io.c b/block/io.c
> index 420944d..0422123 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1745,14 +1745,28 @@ static int64_t coroutine_fn
> bdrv_co_get_block_status_above(BlockDriverState *bs,
>
> assert(bs != base);
> for (p = bs; p != base; p = backing_bs(p)) {
> - ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, pnum,
> file);
> - if (ret < 0 || ret & BDRV_BLOCK_ALLOCATED) {
> - break;
> + int sc;
> + ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, &sc, file);
> + if (ret < 0) {
> + return ret;
> + } else if (ret & BDRV_BLOCK_ALLOCATED) {
> + *pnum = sc;
> + return ret;
> + }
> +
> + /*
> + * [sector_num, nb_sectors] is unallocated on top but intermediate
> + * might have
> + *
> + * [sector_num+x, nr_sectors] allocated.
> + */
> + if (nb_sectors > sc &&
> + (p == bs || sector_num + sc < p->total_sectors)) {
> + nb_sectors = sc;
> }
> - /* [sector_num, pnum] unallocated on this layer, which could be only
> - * the first part of [sector_num, nb_sectors]. */
> - nb_sectors = MIN(nb_sectors, *pnum);
> }
> +
> + *pnum = nb_sectors;
> return ret;
IIUC in the chain image->backing_1->backing_2, where size(image) >
size(backing_1) and size(backing_1) < size(backing_2), if the status of
blocks beyond size(backing_1) is requested we'll start falling through
to backing_2. I'm not certain this is desirable. (And yes, this is
already the case in bdrv_is_allocated_above).
Roman.
