nbd: Simplify client FUA handling

Now that the block layer honors per-bds FUA support, we don't
have to duplicate the fallback flush at the NBD layer.  The
static function nbd_co_writev_flags() is no longer needed, and
the driver can just directly use nbd_client_co_writev().

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/nbd-client.c

@@ -243,15 +243,15 @@ static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num,
 
 static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,
                            int nb_sectors, QEMUIOVector *qiov,
-                           int offset, int *flags)
+                           int offset, int flags)
 {
     NbdClientSession *client = nbd_get_client_session(bs);
     struct nbd_request request = { .type = NBD_CMD_WRITE };
     struct nbd_reply reply;
     ssize_t ret;
 
-    if ((*flags & BDRV_REQ_FUA) && (client->nbdflags & NBD_FLAG_SEND_FUA)) {
-        *flags &= ~BDRV_REQ_FUA;
+    if (flags & BDRV_REQ_FUA) {
+        assert(client->nbdflags & NBD_FLAG_SEND_FUA);
         request.type |= NBD_CMD_FLAG_FUA;
     }
 
@@ -291,7 +291,7 @@ int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,
 }
 
 int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,
-                         int nb_sectors, QEMUIOVector *qiov, int *flags)
+                         int nb_sectors, QEMUIOVector *qiov, int flags)
 {
     int offset = 0;
     int ret;

block/nbd-client.h

@@ -48,7 +48,7 @@ int nbd_client_co_discard(BlockDriverState *bs, int64_t sector_num,
                           int nb_sectors);
 int nbd_client_co_flush(BlockDriverState *bs);
 int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,
-                         int nb_sectors, QEMUIOVector *qiov, int *flags);
+                         int nb_sectors, QEMUIOVector *qiov, int flags);
 int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,
                         int nb_sectors, QEMUIOVector *qiov);
 

block/nbd.c

@@ -355,25 +355,6 @@ static int nbd_co_readv(BlockDriverState *bs, int64_t sector_num,
     return nbd_client_co_readv(bs, sector_num, nb_sectors, qiov);
 }
 
-static int nbd_co_writev_flags(BlockDriverState *bs, int64_t sector_num,
-                               int nb_sectors, QEMUIOVector *qiov, int flags)
-{
-    int ret;
-
-    ret = nbd_client_co_writev(bs, sector_num, nb_sectors, qiov, &flags);
-    if (ret < 0) {
-        return ret;
-    }
-
-    /* The flag wasn't sent to the server, so we need to emulate it with an
-     * explicit flush */
-    if (flags & BDRV_REQ_FUA) {
-        ret = nbd_client_co_flush(bs);
-    }
-
-    return ret;
-}
-
 static int nbd_co_flush(BlockDriverState *bs)
 {
     return nbd_client_co_flush(bs);
@@ -470,7 +451,7 @@ static BlockDriver bdrv_nbd = {
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
     .bdrv_co_readv              = nbd_co_readv,
-    .bdrv_co_writev_flags       = nbd_co_writev_flags,
+    .bdrv_co_writev_flags       = nbd_client_co_writev,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,
@@ -488,7 +469,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
     .bdrv_co_readv              = nbd_co_readv,
-    .bdrv_co_writev_flags       = nbd_co_writev_flags,
+    .bdrv_co_writev_flags       = nbd_client_co_writev,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,
@@ -506,7 +487,7 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
     .bdrv_co_readv              = nbd_co_readv,
-    .bdrv_co_writev_flags       = nbd_co_writev_flags,
+    .bdrv_co_writev_flags       = nbd_client_co_writev,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_discard            = nbd_co_discard,