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qcow2: Zero write support

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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2012-03-20 15:12:58 +01:00
parent ab3a32ad5e
commit 621f058940
4 changed files with 105 additions and 3 deletions
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72
block/qcow2-cluster.c
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@ -1102,3 +1102,75 @@ int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,
return 0;
}
/*
* This zeroes as many clusters of nb_clusters as possible at once (i.e.
* all clusters in the same L2 table) and returns the number of zeroed
* clusters.
*/
static int zero_single_l2(BlockDriverState *bs, uint64_t offset,
unsigned int nb_clusters)
{
BDRVQcowState *s = bs->opaque;
uint64_t *l2_table;
int l2_index;
int ret;
int i;
ret = get_cluster_table(bs, offset, &l2_table, &l2_index);
if (ret < 0) {
return ret;
}
/* Limit nb_clusters to one L2 table */
nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
for (i = 0; i < nb_clusters; i++) {
uint64_t old_offset;
old_offset = be64_to_cpu(l2_table[l2_index + i]);
/* Update L2 entries */
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
if (old_offset & QCOW_OFLAG_COMPRESSED) {
l2_table[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
qcow2_free_any_clusters(bs, old_offset, 1);
} else {
l2_table[l2_index + i] |= cpu_to_be64(QCOW_OFLAG_ZERO);
}
}
ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
if (ret < 0) {
return ret;
}
return nb_clusters;
}
int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors)
{
BDRVQcowState *s = bs->opaque;
unsigned int nb_clusters;
int ret;
/* The zero flag is only supported by version 3 and newer */
if (s->qcow_version < 3) {
return -ENOTSUP;
}
/* Each L2 table is handled by its own loop iteration */
nb_clusters = size_to_clusters(s, nb_sectors << BDRV_SECTOR_BITS);
while (nb_clusters > 0) {
ret = zero_single_l2(bs, offset, nb_clusters);
if (ret < 0) {
return ret;
}
nb_clusters -= ret;
offset += (ret * s->cluster_size);
}
return 0;
}