On 2017-06-13 14:16, Pavel Butsykin wrote: > 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> > --- > block/qcow2-cluster.c | 42 ++++++++++++++++++++++++++++++++ > block/qcow2-refcount.c | 65 > ++++++++++++++++++++++++++++++++++++++++++++++++++ > block/qcow2.c | 40 +++++++++++++++++++++++-------- > block/qcow2.h | 2 ++ > qapi/block-core.json | 3 ++- > 5 files changed, 141 insertions(+), 11 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index d779ea19cf..a84b7e607e 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -32,6 +32,48 @@ > #include "qemu/bswap.h" > #include "trace.h" > > +int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t max_size)
It's not really a max_size but always an exact size. You don't want it
to be any smaller than this.
> +{
> + BDRVQcow2State *s = bs->opaque;
> + int new_l1_size, i, ret;
> +
> + if (max_size >= s->l1_size) {
> + return 0;
> + }
> +
> + new_l1_size = max_size;
> +
> +#ifdef DEBUG_ALLOC2
> + fprintf(stderr, "shrink l1_table from %d to %" PRId64 "\n",
> + s->l1_size, new_l1_size);
new_l1_size is of type int, not int64_t.
> +#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;
> + }
> +
> + 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->l2_size * sizeof(uint64_t),
I'm more of a fan of s->cluster_size instead of s->l2_size *
sizeof(uint64_t) but it's not like it matters...
> + QCOW2_DISCARD_ALWAYS);
> + s->l1_table[i] = 0;
I'd probably clear the overhanging s->l1_table entries before
bdrv_flush() (before you shouldn't really use them after
bdrv_pwrite_zeroes() has returned, even if bdrv_flush() has failed), but
it's not absolutely necessary. As long as they still have a refcount of
at least one, writing to them will just be useless but not destroy any data.
> + }
> + return 0;
> +}
> +
> int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> bool exact_size)
> {
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 576ab551d6..e98306acd8 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -29,6 +29,7 @@
> #include "block/qcow2.h"
> #include "qemu/range.h"
> #include "qemu/bswap.h"
> +#include "qemu/cutils.h"
>
> static int64_t alloc_clusters_noref(BlockDriverState *bs, uint64_t size);
> static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
> @@ -2936,3 +2937,67 @@ done:
> qemu_vfree(new_refblock);
> return ret;
> }
> +
> +int qcow2_shrink_reftable(BlockDriverState *bs)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + uint64_t *reftable_tmp =
> + g_try_malloc(sizeof(uint64_t) * s->refcount_table_size);
> + int i, ret;
> +
> + if (s->refcount_table_size && reftable_tmp == NULL) {
> + return -ENOMEM;
> + }
> +
> + for (i = 0; i < s->refcount_table_size; i++) {
> + int64_t refblock_offs = s->refcount_table[i] & REFT_OFFSET_MASK;
> + void *refblock;
> + bool unused_block;
> +
> + if (refblock_offs == 0) {
> + reftable_tmp[i] = 0;
> + continue;
> + }
> + ret = qcow2_cache_get(bs, s->refcount_block_cache, refblock_offs,
> + &refblock);
> + if (ret < 0) {
> + goto out;
> + }
> +
> + /* the refblock has own reference */
> + if (i == refblock_offs >> (s->refcount_block_bits +
> s->cluster_bits)) {
> + uint64_t blk_index = (refblock_offs >> s->cluster_bits) &
> + (s->refcount_block_size - 1);
> + uint64_t refcount = s->get_refcount(refblock, blk_index);
> +
> + s->set_refcount(refblock, blk_index, 0);
> +
> + unused_block = buffer_is_zero(refblock, s->refcount_block_size);
s/refcount_block_size/cluster_size/
> +
> + s->set_refcount(refblock, blk_index, refcount);
> + } else {
> + unused_block = buffer_is_zero(refblock, s->refcount_block_size);
Same here.
> + }
> + qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
> +
> + reftable_tmp[i] = unused_block ? 0 :
> cpu_to_be64(s->refcount_table[i]);
> + }
> +
> + ret = bdrv_pwrite_sync(bs->file, s->refcount_table_offset, reftable_tmp,
> + sizeof(uint64_t) * s->refcount_table_size);
> + if (ret < 0) {
> + goto out;
> + }
> +
> + for (i = 0; i < s->refcount_table_size; i++) {
> + if (s->refcount_table[i] && !reftable_tmp[i]) {
> + qcow2_free_clusters(bs, s->refcount_table[i] & REFT_OFFSET_MASK,
> + s->cluster_size, QCOW2_DISCARD_ALWAYS);
This doesn't feel like a very good idea. The bdrv_pwrite_sync() before
has brought the on-disk refcount structures into a different state than
what we have cached.
OTOH, the bdrv_pwrite_sync() has accessed only the reftable and this
should only access refblocks. So I cannot think of any way this might
actually do something bad. But I guess it'll be better for to revisit
this when it's not in the middle of the night (so on Friday).
> + s->refcount_table[i] = 0;
> + }
> + }
> +
> +out:
> + g_free(reftable_tmp);
> + return ret;
> +}
> diff --git a/block/qcow2.c b/block/qcow2.c
> index b3ba5daa93..0ad46d2776 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2545,6 +2545,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t
> offset, Error **errp)
> {
> BDRVQcow2State *s = bs->opaque;
> int64_t new_l1_size;
> + uint64_t total_size;
> int ret;
>
> if (offset & 511) {
> @@ -2558,17 +2559,36 @@ static int qcow2_truncate(BlockDriverState *bs,
> int64_t offset, Error **errp)
> return -ENOTSUP;
> }
>
> - /* shrinking is currently not supported */
> - if (offset < bs->total_sectors * 512) {
> - error_setg(errp, "qcow2 doesn't support shrinking images yet");
> - return -ENOTSUP;
> - }
> -
> new_l1_size = size_to_l1(s, offset);
> - ret = qcow2_grow_l1_table(bs, new_l1_size, true);
> - if (ret < 0) {
> - error_setg_errno(errp, -ret, "Failed to grow the L1 table");
> - return ret;
> + total_size = bs->total_sectors << BDRV_SECTOR_BITS;
> +
> + if (offset < total_size) {
> + ret = qcow2_cluster_discard(bs, ROUND_UP(offset, s->cluster_size),
> + total_size - ROUND_UP(offset,
> + s->cluster_size),
> + QCOW2_DISCARD_ALWAYS, true);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Failed to discard reduced
> clasters");
s/clasters/clusters/
And maybe "truncated", "stripped", or "cropped" instead of "reduced"?
> + return ret;
> + }
> +
> + ret = qcow2_shrink_l1_table(bs, new_l1_size);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Failed to reduce the L1 table");
s/reduce/shrink/ (or "truncate"; or "reduce the L1 table size")
Also, to be fair, you're actually reducing the number of L2 tables, not
the size of the L1 table. (But that's a nit pick)
> + return ret;
> + }
> +
> + ret = qcow2_shrink_reftable(bs);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Failed to shrink the refcount
> table");
And this is not really shrinking the reftable but instead discarding
some refblocks (potentially). (This is a nit pick, too)
Max
> + return ret;
> + }
> + } else {
> + ret = qcow2_grow_l1_table(bs, new_l1_size, true);
> + if (ret < 0) {
> + error_setg_errno(errp, -ret, "Failed to grow the L1 table");
> + return ret;
> + }
> }
>
> /* write updated header.size */
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 07faa6dc78..600463bf8e 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -531,10 +531,12 @@ int qcow2_pre_write_overlap_check(BlockDriverState *bs,
> int ign, int64_t offset,
> int qcow2_change_refcount_order(BlockDriverState *bs, int refcount_order,
> BlockDriverAmendStatusCB *status_cb,
> void *cb_opaque, Error **errp);
> +int qcow2_shrink_reftable(BlockDriverState *bs);
>
> /* qcow2-cluster.c functions */
> int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> bool exact_size);
> +int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t max_size);
> int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index);
> int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset);
> int qcow2_encrypt_sectors(BDRVQcow2State *s, int64_t sector_num,
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index f85c2235c7..bcbffa3339 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2372,7 +2372,8 @@
> 'cluster_alloc_bytes', 'cluster_free', 'flush_to_os',
> 'flush_to_disk', 'pwritev_rmw_head', 'pwritev_rmw_after_head',
> 'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
> - 'pwritev_zero', 'pwritev_done', 'empty_image_prepare' ] }
> + 'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
> + 'l1_shrink_write_table', 'l1_shrink_free_l2_clusters' ] }
>
> ##
> # @BlkdebugInjectErrorOptions:
>
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