[PATCH 6/9] ssh: Support BDRV_REQ_ZERO_WRITE for truncate

[Eric Blake <eblake@redhat.com>]

Our .bdrv_has_zero_init_truncate can detect when the remote side
always zero fills; we can reuse that same knowledge to implement
BDRV_REQ_ZERO_WRITE by ignoring it when the server gives it to us for
free.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/ssh.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/ssh.c b/block/ssh.c
index 9eb33df8598c..f9e08a490069 100644
--- a/block/ssh.c
+++ b/block/ssh.c
@@ -883,6 +883,10 @@ static int ssh_file_open(BlockDriverState *bs, QDict *options, int bdrv_flags,
     /* Go non-blocking. */
     ssh_set_blocking(s->session, 0);

+    if (s->attrs->type == SSH_FILEXFER_TYPE_REGULAR) {
+        bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
+    }
+
     qapi_free_BlockdevOptionsSsh(opts);

     return 0;
-- 
2.26.2