nbd: zero from and len fields in NBD_CMD_DISCONNECT.

Len field is already set to zero, but not the from field which is sent
as 0xfffffffffffffe00.  This makes no sense, and may cause confuse
server implementations doing sanity checks (qemu-nbd is an example.)

Signed-off-by: Hani Benhabiles <hani@linux.com>
Cc: Paul Clements <paul.clements@us.sios.com>
Cc: Paul Clements <Paul.Clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/nbd.c

@@ -243,14 +243,11 @@ static int nbd_send_req(struct nbd_device *nbd, struct request *req)
 	struct nbd_request request;
 	unsigned long size = blk_rq_bytes(req);
 
+	memset(&request, 0, sizeof(request));
 	request.magic = htonl(NBD_REQUEST_MAGIC);
 	request.type = htonl(nbd_cmd(req));
 
-	if (nbd_cmd(req) == NBD_CMD_FLUSH) {
-		/* Other values are reserved for FLUSH requests.  */
-		request.from = 0;
-		request.len = 0;
-	} else {
+	if (nbd_cmd(req) != NBD_CMD_FLUSH && nbd_cmd(req) != NBD_CMD_DISC) {
 		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
 		request.len = htonl(size);
 	}