On 2017-09-28 11:27, 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>
> Reviewed-by: John Snow <js...@redhat.com>
> ---
> block/qcow2-refcount.c | 22 ++++++++++++++++++++++
> block/qcow2.c | 23 +++++++++++++++++++++++
> block/qcow2.h | 1 +
> 3 files changed, 46 insertions(+)
>
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 88d5a3f1ad..aa3fd6cf17 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -3181,3 +3181,25 @@ 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;
> +
> + for (i = size_to_clusters(s, size) - 1; i >= 0; i--) {
> + uint64_t refcount;
> + 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));
> + return ret;
> + }
> + if (refcount > 0) {
> + return i;
> + }
> + }
> + qcow2_signal_corruption(bs, true, -1, -1,
> + "There are no references in the refcount
> table.");
> + return -EIO;
> +}
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 8a4311d338..f08c69ccd9 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -3106,6 +3106,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t
> offset,
> new_l1_size = size_to_l1(s, offset);
>
> if (offset < old_length) {
> + int64_t last_cluster, old_file_size;
> if (prealloc != PREALLOC_MODE_OFF) {
> error_setg(errp,
> "Preallocation can't be used for shrinking an image");
> @@ -3134,6 +3135,28 @@ static int qcow2_truncate(BlockDriverState *bs,
> int64_t offset,
> "Failed to discard unused refblocks");
> return ret;
> }
> +
> + old_file_size = bdrv_getlength(bs->file->bs);
> + if (old_file_size < 0) {
> + error_setg_errno(errp, -old_file_size,
> + "Failed to inquire current file length");
> + return old_file_size;
> + }
> + last_cluster = qcow2_get_last_cluster(bs, old_file_size);
> + if (last_cluster < 0) {
> + error_setg_errno(errp, -last_cluster,
> + "Failed to find the last cluster");
> + return last_cluster;
> + }
> + if ((last_cluster + 1) * s->cluster_size < old_file_size) {
> + ret = bdrv_truncate(bs->file, (last_cluster + 1) *
> s->cluster_size,
> + PREALLOC_MODE_OFF, NULL);
> + if (ret < 0) {
> + warn_report("Failed to truncate the tail of the image: "
> + "ret = %d", ret);
How about using strerror(-ret) instead?
Max
> + ret = 0;
> + }
> + }
> } else {
> ret = qcow2_grow_l1_table(bs, new_l1_size, true);
> if (ret < 0) {
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 5a289a81e2..782a206ecb 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -597,6 +597,7 @@ int qcow2_change_refcount_order(BlockDriverState *bs, int
> refcount_order,
> BlockDriverAmendStatusCB *status_cb,
> void *cb_opaque, Error **errp);
> int qcow2_shrink_reftable(BlockDriverState *bs);
> +int64_t qcow2_get_last_cluster(BlockDriverState *bs, int64_t size);
>
> /* qcow2-cluster.c functions */
> int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
>
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