[PATCH 3/9] nfs: Support BDRV_REQ_ZERO_WRITE for truncate

[Eric Blake]

Our .bdrv_has_zero_init_truncate returns 1 if we detect that the OS
always 0-fills; we can use that same knowledge to implement
BDRV_REQ_ZERO_WRITE by ignoring it when the OS gives it to us for
free.

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

diff --git a/block/nfs.c b/block/nfs.c
index 2393fbfe6bcc..b93989265630 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -623,6 +623,9 @@ static int nfs_file_open(BlockDriverState *bs, QDict 
*options, int flags,
     }

     bs->total_sectors = ret;
+    if (client->has_zero_init) {
+        bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
+    }
     ret = 0;
     return ret;
 }
-- 
2.26.2