offset, bytes, pnum, map, file);
}
+/*
+ * Check @bs (and its backing chain) to see if the range defined
+ * by @offset and @bytes is known to read as zeroes.
+ * Return 1 if that is the case, 0 otherwise and -errno on error.
+ * This test is meant to be fast rather than accurate so returning 0
+ * does not guarantee non-zero data.
+ */
+int coroutine_fn bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset,
+ int64_t bytes)
+{
+ int ret;
+ int64_t pnum = bytes;
+
+ if (!bytes) {
+ return 1;
+ }
+
+ ret = bdrv_common_block_status_above(bs, NULL, false, false, offset,
+ bytes, &pnum, NULL, NULL);
+
+ if (ret < 0) {
+ return ret;
+ }
+
+ return (pnum == bytes) && (ret & BDRV_BLOCK_ZERO);
+}
+
int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
int64_t bytes, int64_t *pnum)
{
return false;
}
-static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes)
-{
- int64_t nr;
- return !bytes ||
- (!bdrv_is_allocated_above(bs, NULL, false, offset, bytes, &nr) &&
- nr == bytes);
-}
-
-static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
+/*
+ * Return 1 if the COW regions read as zeroes, 0 if not, < 0 on error.
+ * Note that returning 0 does not guarantee non-zero data.
+ */
+static int is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
{
/*
* This check is designed for optimization shortcut so it must be
* efficient.
- * Instead of is_zero(), use is_unallocated() as it is faster (but not
- * as accurate and can result in false negatives).
+ * Instead of is_zero(), use bdrv_co_is_zero_fast() as it is
+ * faster (but not as accurate and can result in false negatives).
*/
- return is_unallocated(bs, m->offset + m->cow_start.offset,
- m->cow_start.nb_bytes) &&
- is_unallocated(bs, m->offset + m->cow_end.offset,
- m->cow_end.nb_bytes);
+ int ret = bdrv_co_is_zero_fast(bs, m->offset + m->cow_start.offset,
+ m->cow_start.nb_bytes);
+ if (ret <= 0) {
+ return ret;
+ }
+
+ return bdrv_co_is_zero_fast(bs, m->offset + m->cow_end.offset,
+ m->cow_end.nb_bytes);
}
static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
continue;
}
- if (!is_zero_cow(bs, m)) {
+ ret = is_zero_cow(bs, m);
+ if (ret < 0) {
+ return ret;
+ } else if (ret == 0) {
continue;
}
int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
bool include_base, int64_t offset, int64_t bytes,
int64_t *pnum);
+int coroutine_fn bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset,
+ int64_t bytes);
bool bdrv_is_read_only(BlockDriverState *bs);
int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only,