[RFC PATCH 09/22] nbd: Add writethrough to block-export-add

[Kevin Wolf <kwolf@redhat.com>]

qemu-nbd allows use of writethrough cache modes, which mean that write
requests made through NBD will cause a flush before they complete.
Expose the same functionality in block-export-add.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qapi/block-export.json | 7 ++++++-
 blockdev-nbd.c         | 2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/qapi/block-export.json b/qapi/block-export.json
index 1fdc55c53a..4ce163411f 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -167,10 +167,15 @@
 # Describes a block export, i.e. how single node should be exported on an
 # external interface.
 #
+# @writethrough: If true, caches are flushed after every write request to the
+#                export before completion is signalled. (since: 5.2;
+#                default: false)
+#
 # Since: 4.2
 ##
 { 'union': 'BlockExportOptions',
-  'base': { 'type': 'BlockExportType' },
+  'base': { 'type': 'BlockExportType',
+            '*writethrough': 'bool' },
   'discriminator': 'type',
   'data': {
       'nbd': 'BlockExportOptionsNbd'
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 28159a92b2..17417c1b6b 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -218,7 +218,7 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 
     exp = nbd_export_new(bs, arg->name, arg->description, arg->bitmap,
                          !arg->writable, !arg->writable,
-                         NULL, false, errp);
+                         NULL, exp_args->writethrough, errp);
     if (!exp) {
         goto out;
     }
-- 
2.25.4