[PATCH] null_blk: Add notes to use LightNVM

[Yasuaki Ishimatsu]

If CONFIG_NVM is disabled, loading null_block module with use_lightnvm=1
fails. But there are no messages and documents related to the failure.

So the patch adds the notes to use LightNVM.

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
---
 Documentation/block/null_blk.txt | 2 +-
 drivers/block/null_blk.c         | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/block/null_blk.txt b/Documentation/block/null_blk.txt
index d8880ca..0365a26 100644
--- a/Documentation/block/null_blk.txt
+++ b/Documentation/block/null_blk.txt
@@ -72,4 +72,4 @@ use_per_node_hctx=[0/1]: Default: 0
      queue for each CPU node in the system.

 use_lightnvm=[0/1]: Default: 0
-  Register device with LightNVM. Requires blk-mq to be used.
+  Register device with LightNVM. Requires blk-mq and CONFIG_NVM=y to be used.
diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index ba6f4a2e..4943ee2 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -577,6 +577,7 @@ static void null_nvm_unregister(struct nullb *nullb)
 #else
 static int null_nvm_register(struct nullb *nullb)
 {
+	pr_err("null_blk: CONFIG_NVM needs to be enabled for LightNVM\n");
 	return -EINVAL;
 }
 static void null_nvm_unregister(struct nullb *nullb) {}
--
1.8.3.1