Several drivers supply .bdrv_has_zero_init that returns 1, but lack
the .bdrv_has_zero_init_truncate callback (parallels and qed outright,
vdi in some scenarios). A literal reading of the existing
documentation says such drivers are broken, because
bdrv_has_zero_init_truncate() defaults to zero if the callback is
missing; but in practice, the tie between the two functions is only
relevant when truncate is supported. Clarify the documentation to
make it obvious that this is okay.
Fixes: 1dcaf527
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
include/block/block_int.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 640fb82c789e..77ab45dc87cf 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -444,7 +444,8 @@ struct BlockDriver {
/*
* Returns 1 if newly created images are guaranteed to contain only
* zeros, 0 otherwise.
- * Must return 0 if .bdrv_has_zero_init_truncate() returns 0.
+ * Must return 0 if .bdrv_co_truncate is set and
+ * .bdrv_has_zero_init_truncate() returns 0.
*/
int (*bdrv_has_zero_init)(BlockDriverState *bs);
--
2.24.1
