If a qcow2 file is preallocated, it can no longer guarantee that it
initially appears as filled with zeroes.
So implement .bdrv_has_zero_init() by checking whether the file is
preallocated; if so, forward the call to the underlying storage node,
except for when it is encrypted: Encrypted preallocated images always
return effectively random data, so .bdrv_has_zero_init() must always
return 0 for them.
Reported-by: Stefano Garzarella <sgarz...@redhat.com>
Signed-off-by: Max Reitz <mre...@redhat.com>
---
block/qcow2.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 89 insertions(+), 1 deletion(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index 039bdc2f7e..730fd53890 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4631,6 +4631,94 @@ static ImageInfoSpecific
*qcow2_get_specific_info(BlockDriverState *bs,
return spec_info;
}
+/*
+ * Return 1 if the file only contains zero and unallocated clusters.
+ * Return 0 if it contains compressed or normal clusters.
+ * Return -errno on error.
+ */
+static int qcow2_is_zero(BlockDriverState *bs)
+{
+ BDRVQcow2State *s = bs->opaque;
+ int l1_i;
+ int ret;
+
+ if (bs->backing) {
+ return 0;
+ }
+
+ for (l1_i = 0; l1_i < s->l1_size; l1_i++) {
+ uint64_t l2_offset = s->l1_table[l1_i] & L1E_OFFSET_MASK;
+ int slice_start_i;
+
+ if (!l2_offset) {
+ continue;
+ }
+
+ for (slice_start_i = 0; slice_start_i < s->l2_size;
+ slice_start_i += s->l2_slice_size)
+ {
+ uint64_t *l2_slice;
+ int l2_slice_i;
+
+ ret = qcow2_cache_get(bs, s->l2_table_cache,
+ l2_offset + slice_start_i * sizeof(uint64_t),
+ (void **)&l2_slice);
+ if (ret < 0) {
+ return ret;
+ }
+
+ for (l2_slice_i = 0; l2_slice_i < s->l2_slice_size; l2_slice_i++) {
+ uint64_t l2_entry = be64_to_cpu(l2_slice[l2_slice_i]);
+
+ switch (qcow2_get_cluster_type(bs, l2_entry)) {
+ case QCOW2_CLUSTER_UNALLOCATED:
+ case QCOW2_CLUSTER_ZERO_PLAIN:
+ case QCOW2_CLUSTER_ZERO_ALLOC:
+ break;
+
+ case QCOW2_CLUSTER_NORMAL:
+ case QCOW2_CLUSTER_COMPRESSED:
+ qcow2_cache_put(s->l2_table_cache, (void **)&l2_slice);
+ return 0;
+
+ default:
+ abort();
+ }
+ }
+
+ qcow2_cache_put(s->l2_table_cache, (void **)&l2_slice);
+ }
+ }
+
+ return 1;
+}
+
+static int qcow2_has_zero_init(BlockDriverState *bs)
+{
+ BDRVQcow2State *s = bs->opaque;
+ int ret;
+
+ if (qemu_in_coroutine()) {
+ qemu_co_mutex_lock(&s->lock);
+ }
+ /* Check preallocation status */
+ ret = qcow2_is_zero(bs);
+ if (qemu_in_coroutine()) {
+ qemu_co_mutex_unlock(&s->lock);
+ }
+ if (ret < 0) {
+ return 0;
+ }
+
+ if (ret == 1) {
+ return 1;
+ } else if (bs->encrypted) {
+ return 0;
+ } else {
+ return bdrv_has_zero_init(s->data_file->bs);
+ }
+}
+
static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
int64_t pos)
{
@@ -5186,7 +5274,7 @@ BlockDriver bdrv_qcow2 = {
.bdrv_child_perm = bdrv_format_default_perms,
.bdrv_co_create_opts = qcow2_co_create_opts,
.bdrv_co_create = qcow2_co_create,
- .bdrv_has_zero_init = bdrv_has_zero_init_1,
+ .bdrv_has_zero_init = qcow2_has_zero_init,
.bdrv_co_block_status = qcow2_co_block_status,
.bdrv_co_preadv = qcow2_co_preadv,
--
2.21.0
