Am 17.04.2014 um 23:59 hat Max Reitz geschrieben:
> Implement bdrv_make_empty() by making all clusters in the image fall
> through to the backing file (via the now modified discard).
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> block/qcow2.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 1e7b7d5..4d70665 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2006,6 +2006,27 @@ fail:
> return ret;
> }
>
> +static int qcow2_make_empty(BlockDriverState *bs)
> +{
> + uint64_t start_sector;
> + int ret = 0;
> +
> + /* The step taken here may not exceed INT_MAX when multiplied by
> + * BDRV_SECTOR_SIZE. 64k is arbitrary, but works well. */
So you really mean something like this?
int max_sectors_per_iteration = (INT_MAX / BDRV_SECTOR_SIZE);
> + for (start_sector = 0; start_sector < bs->total_sectors;
> + start_sector += 65536)
> + {
> + ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE,
> + MIN(65536, bs->total_sectors - start_sector),
> + QCOW2_DISCARD_REQUEST, true);
QCOW2_DISCARD_REQUEST is for requests that come from the guest. SNAPSHOT
would be a nice fit if we reinterpreted it so that it doesn't only refer
to internal snapshots but also to external ones. I would be okay with
OTHER as well if you prefer.
Perhaps a look at the defaults can help us: SNAPSHOT defaults to on,
OTHER to off. I think it totally makes sense to physically discard
clusters in qcow2_make_empty() in almost every case, so that might be a
good reason to use SNAPSHOT here.
> + if (ret < 0) {
> + break;
> + }
> + }
> +
> + return ret;
> +}
> +
Kevin
