[PATCH 4/9] rbd: Support BDRV_REQ_ZERO_WRITE for truncate

[Eric Blake]

Our .bdrv_has_zero_init_truncate always returns 1 because rbd always
0-fills; we can use that same knowledge to implement
BDRV_REQ_ZERO_WRITE by ignoring it.

Signed-off-by: Eric Blake <address@hidden>
---
 block/rbd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/rbd.c b/block/rbd.c
index f2d52091c702..331c45adb2b2 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -817,6 +817,9 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict 
*options, int flags,
         }
     }

+    /* When extending regular files, we get zeros from the OS */
+    bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
+
     r = 0;
     goto out;

-- 
2.26.2