nvmet: use IOCB_NOWAIT only if the filesystem supports it

Submit I/O requests with the IOCB_NOWAIT flag set only if
the underlying filesystem supports it.

Fixes: 50a909db ("nvmet: use IOCB_NOWAIT for file-ns buffered I/O")
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/io-cmd-file.c

@@ -8,6 +8,7 @@
 #include <linux/uio.h>
 #include <linux/falloc.h>
 #include <linux/file.h>
+#include <linux/fs.h>
 #include "nvmet.h"
 
 #define NVMET_MAX_MPOOL_BVEC		16
@@ -266,6 +267,7 @@ static void nvmet_file_execute_rw(struct nvmet_req *req)
 
 	if (req->ns->buffered_io) {
 		if (likely(!req->f.mpool_alloc) &&
+		    (req->ns->file->f_mode & FMODE_NOWAIT) &&
 		    nvmet_file_execute_io(req, IOCB_NOWAIT))
 			return;
 		nvmet_file_submit_buffered_io(req);