On 2017-08-17 11:15, 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 <[email protected]> > Reviewed-by: Max Reitz <[email protected]> > --- > block/qcow2-cluster.c | 50 +++++++++++++++++++++ > block/qcow2-refcount.c | 120 > +++++++++++++++++++++++++++++++++++++++++++++++++ > block/qcow2.c | 43 ++++++++++++++---- > block/qcow2.h | 14 ++++++ > qapi/block-core.json | 3 +- > 5 files changed, 220 insertions(+), 10 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index f06c08f64c..0c7a9a920c 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -32,6 +32,56 @@ > #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 + > + new_l1_size * sizeof(uint64_t), > + (s->l1_size - new_l1_size) * sizeof(uint64_t), > 0); > + if (ret < 0) { > + goto fail; > + } > + > + ret = bdrv_flush(bs->file->bs); > + if (ret < 0) { > + goto fail; > + } > + > + 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; > + > +fail: > + /* > + * If the write in the l1_table failed the image may contain partially > + * overwritten the l1_table. In this case would be better to clear the
e.g. *"may contain a partially overwritten l1_table"
*"In this case it would be better"
> + * l1_table in memory to avoid possible image corruption.
> + */
> + memset(s->l1_table + exact_size, 0,
Though it doesn't make a functional difference, I'd prefer "new_l1_size"
instead of "exact_size", because you're using new_l1_size everywhere
else (including the line below).
> + (s->l1_size - new_l1_size) * sizeof(uint64_t));
> + return ret;
> +}
> +
> 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 8c17c0e3aa..15af9a795f 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,
> @@ -3061,3 +3062,122 @@ done:
> qemu_vfree(new_refblock);
> return ret;
> }
> +
> +static int qcow2_discard_refcount_block(BlockDriverState *bs,
> + uint64_t discard_block_offs)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + uint64_t refblock_offs = get_refblock_offset(s, discard_block_offs);
> + uint64_t cluster_index = discard_block_offs >> s->cluster_bits;
> + uint32_t block_index = cluster_index & (s->refcount_block_size - 1);
> + void *refblock;
> + int ret;
> +
> + assert(discard_block_offs != 0);
> +
> + ret = qcow2_cache_get(bs, s->refcount_block_cache, refblock_offs,
> + &refblock);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + if (s->get_refcount(refblock, block_index) != 1) {
> + qcow2_signal_corruption(bs, true, -1, -1, "Invalid refcount:"
> + " refblock offset %#" PRIx64
> + ", reftable index %u"
> + ", block offset %#" PRIx64
> + ", refcount %#" PRIx64,
> + refblock_offs,
> + offset_to_reftable_index(s,
> discard_block_offs),
> + discard_block_offs,
> + s->get_refcount(refblock, block_index));
> + qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
> + return -EINVAL;
> + }
> + s->set_refcount(refblock, block_index, 0);
> +
> + qcow2_cache_entry_mark_dirty(bs, s->refcount_block_cache, refblock);
> +
> + qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
> +
> + if (cluster_index < s->free_cluster_index) {
> + s->free_cluster_index = cluster_index;
> + }
> +
> + refblock = qcow2_cache_is_table_offset(bs, s->refcount_block_cache,
> + discard_block_offs);
> + if (refblock) {
> + /* discard refblock from the cache if refblock is cached */
> + qcow2_cache_discard(bs, s->refcount_block_cache, refblock);
> + }
> + update_refcount_discard(bs, discard_block_offs, s->cluster_size);
> +
> + return 0;
> +}
> +
> +int qcow2_shrink_reftable(BlockDriverState *bs)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + uint64_t *reftable_tmp =
> + g_malloc(s->refcount_table_size * sizeof(uint64_t));
> + int i, ret;
> +
> + 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 == offset_to_reftable_index(s, refblock_offs)) {
> + uint64_t block_index = (refblock_offs >> s->cluster_bits) &
> + (s->refcount_block_size - 1);
> + uint64_t refcount = s->get_refcount(refblock, block_index);
> +
> + s->set_refcount(refblock, block_index, 0);
> +
> + unused_block = buffer_is_zero(refblock, s->cluster_size);
> +
> + s->set_refcount(refblock, block_index, refcount);
> + } else {
> + unused_block = buffer_is_zero(refblock, s->cluster_size);
> + }
> + 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,
> + s->refcount_table_size * sizeof(uint64_t));
> + /*
> + * If the write in the reftable failed the image may contain partially
> + * overwritten the reftable. In this case would be better to clear the
*"may contain a partially overwritten reftable"
*"In this case it would be better"
With these changes:
Reviewed-by: Max Reitz <[email protected]>
> + * reftable in memory to avoid possible image corruption.
> + */
> + for (i = 0; i < s->refcount_table_size; i++) {
> + if (s->refcount_table[i] && !reftable_tmp[i]) {
> + if (ret == 0) {
> + ret = qcow2_discard_refcount_block(bs, s->refcount_table[i] &
> + REFT_OFFSET_MASK);
> + }
> + s->refcount_table[i] = 0;
> + }
> + }
> +
> + if (!s->cache_discards) {
> + qcow2_process_discards(bs, ret);
> + }
> +
> +out:
> + g_free(reftable_tmp);
> + return ret;
> +}
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