From: Chaitanya Kulkarni <kch@nvidia.com>
Date: Wed, 2 Feb 2022 01:04:45 -0800
Subject: nvmet: allow bdev in buffered_io mode
Patch-mainline: v5.18-rc1
Git-commit: 6f6d604b4ef896793901f213db3b45eefa7288fa
References: jsc#PED-1183

Allow block device to be configured in the buffered I/O mode by using
the file backend. In this way now we can use cache for the block
device namespace which shows significant performance improvement.

We update the block device ns enable function and return early when
buffered_io flag is set.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 drivers/nvme/target/io-cmd-bdev.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -76,6 +76,14 @@ int nvmet_bdev_ns_enable(struct nvmet_ns
 {
 	int ret;
 
+	/*
+	 * When buffered_io namespace attribute is enabled that means user want
+	 * this block device to be used as a file, so block device can take
+	 * an advantage of cache.
+	 */
+	if (ns->buffered_io)
+		return -ENOTBLK;
+
 	ns->bdev = blkdev_get_by_path(ns->device_path,
 			FMODE_READ | FMODE_WRITE, NULL);
 	if (IS_ERR(ns->bdev)) {