From 7fc4405c5d29dd580b403e927ff4afe7c12949f5 Mon Sep 17 00:00:00 2001
From: Daniel Verkamp <daniel.verkamp@intel.com>
Date: Fri, 1 Sep 2017 16:27:28 -0700
Subject: [PATCH] doc/bdev: document bdev_null

Change-Id: I5b48e798b0540ef7fbc99699ebf6dc913c075b44
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/376861
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
---
 doc/bdev.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/doc/bdev.md b/doc/bdev.md
index d368986dd..c10557843 100644
--- a/doc/bdev.md
+++ b/doc/bdev.md
@@ -57,6 +57,21 @@ Configuration file syntax:
 This exports 4 malloc block devices, named Malloc0 through Malloc3.  Each malloc block device will
 be 64MB in size.
 
+## Null {#bdev_config_null}
+
+The SPDK null bdev driver is a dummy block I/O target that discards all writes and returns undefined
+data for reads.  It is useful for benchmarking the rest of the bdev I/O stack with minimal block
+device overhead and for testing configurations that can't easily be created with the Malloc bdev.
+
+Configuration file syntax:
+~~~
+[Null]
+  # Dev <name> <size_in_MiB> <block_size>
+
+  # Create an 8 petabyte null bdev with 4K block size called Null0
+  Dev Null0 8589934592 4096
+ ~~~
+
 ## Linux AIO {#bdev_config_aio}
 
 The SPDK aio bdev driver provides SPDK block layer access to Linux kernel block devices via Linux AIO.