Am 12.07.2017 um 13:46 hat Pavel Butsykin geschrieben:
> This patch add shrinking of the image file for qcow2. As a result, this allows
> us to reduce the virtual image size and free up space on the disk without
> copying the image. Image can be fragmented and shrink is done by punching
> holes
> in the image file.
>
> Signed-off-by: Pavel Butsykin <pbutsy...@virtuozzo.com>
> Reviewed-by: Max Reitz <mre...@redhat.com>
> ---
> block/qcow2-cluster.c | 40 ++++++++++++++++++
> block/qcow2-refcount.c | 110
> +++++++++++++++++++++++++++++++++++++++++++++++++
> block/qcow2.c | 43 +++++++++++++++----
> block/qcow2.h | 14 +++++++
> qapi/block-core.json | 3 +-
> 5 files changed, 200 insertions(+), 10 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index f06c08f64c..518429c64b 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -32,6 +32,46 @@
> #include "qemu/bswap.h"
> #include "trace.h"
>
> +int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t exact_size)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + int new_l1_size, i, ret;
> +
> + if (exact_size >= s->l1_size) {
> + return 0;
> + }
> +
> + new_l1_size = exact_size;
> +
> +#ifdef DEBUG_ALLOC2
> + fprintf(stderr, "shrink l1_table from %d to %d\n", s->l1_size,
> new_l1_size);
> +#endif
> +
> + BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_WRITE_TABLE);
> + ret = bdrv_pwrite_zeroes(bs->file, s->l1_table_offset +
> + sizeof(uint64_t) * new_l1_size,
> + (s->l1_size - new_l1_size) * sizeof(uint64_t),
> 0);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + ret = bdrv_flush(bs->file->bs);
> + if (ret < 0) {
> + return ret;
> + }
If we have an error here (or after a partial bdrv_pwrite_zeroes()), we
have entries zeroed out on disk, but in memory we still have the
original L1 table.
Should the in-memory L1 table be zeroed first? Then we can't
accidentally reuse stale entries, but would have to allocate new ones,
which would get on-disk state and in-memory state back in sync again.
> + BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_FREE_L2_CLUSTERS);
> + for (i = s->l1_size - 1; i > new_l1_size - 1; i--) {
> + if ((s->l1_table[i] & L1E_OFFSET_MASK) == 0) {
> + continue;
> + }
> + qcow2_free_clusters(bs, s->l1_table[i] & L1E_OFFSET_MASK,
> + s->cluster_size, QCOW2_DISCARD_ALWAYS);
> + s->l1_table[i] = 0;
> + }
> + return 0;
> +}
> +
> int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> bool exact_size)
> {
I haven't checked qcow2_shrink_reftable() for similar kinds of problems,
I hope Max has.
Kevin
