On 2017-09-20 15:58, Pavel Butsykin wrote:
> Now after shrinking the image, at the end of the image file, there might be a
> tail that probably will never be used. So we can find the last used cluster
> and
> cut the tail.
>
> Signed-off-by: Pavel Butsykin <pbutsy...@virtuozzo.com>
> ---
> block/qcow2-refcount.c | 21 +++++++++++++++++++++
> block/qcow2.c | 19 +++++++++++++++++++
> block/qcow2.h | 1 +
> 3 files changed, 41 insertions(+)
>
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 88d5a3f1ad..5e221a166c 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -3181,3 +3181,24 @@ out:
> g_free(reftable_tmp);
> return ret;
> }
> +
> +int64_t qcow2_get_last_cluster(BlockDriverState *bs, int64_t size)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + int64_t i, last_cluster, nb_clusters = size_to_clusters(s, size);
> + uint64_t refcount;
> +
> + for (i = 0, last_cluster = 0; i < nb_clusters; i++) {
> + int ret = qcow2_get_refcount(bs, i, &refcount);
> + if (ret < 0) {
> + fprintf(stderr, "Can't get refcount for cluster %" PRId64 ":
> %s\n",
> + i, strerror(-ret));
> + continue;
Oh, and another thing: If you decide to ignore errors here, I'd at least
consider the cluster allocated.
Of course it would also be possible not to ignore errors, and instead
return them to the caller which would then just not truncate the file.
Max
> + }
> +
> + if (refcount > 0) {
> + last_cluster = i;
> + }
> + }
> + return last_cluster;
> +}
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