commit 8f23aaf5d6a5458e251c5d5d0555d9e515355e35
author Eric Blake <eblake@redhat.com> Tue Apr 28 15:28:59 2020 -0500
committer Kevin Wolf <kwolf@redhat.com> Fri May 08 13:26:35 2020 +0200
tree 222449c884848e6ede2fb43e7d0343372aa91192
parent 8e519795041e3293ab6b4e67f5416fa80dc0efc4

nfs: Support BDRV_REQ_ZERO_WRITE for truncate

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 <eblake@redhat.com>
Message-Id: <20200428202905.770727-4-eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/nfs.c

diff --git a/block/nfs.c b/block/nfs.c
index 385d756..76daa7c 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -620,6 +620,9 @@
     }
 
     bs->total_sectors = ret;
+    if (client->has_zero_init) {
+        bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
+    }
     return 0;
 }