[PATCH v2 2/3] docs/nvdimm: add description of alignment requirement of device dax

[Jingqi Liu <jingqi.liu@intel.com>]

For device dax (e.g., /dev/dax0.0), the NUM of 'align=NUM' option
needs to match the alignment requirement of the device dax.
It must be larger than or equal to the 'align' of device dax.

Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
---
 docs/nvdimm.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index 362e99109e..3c7b6dab5f 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -132,6 +132,15 @@ address to the page size (getpagesize(2)) by default. However, some
 types of backends may require an alignment different than the page
 size. In that case, QEMU v2.12.0 and later provide 'align' option to
 memory-backend-file to allow users to specify the proper alignment.
+For device dax (e.g., /dev/dax0.0), this alignment needs to match the
+alignment requirement of the device dax. The NUM of 'align=NUM' option
+must be larger than or equal to the 'align' of device dax.
+We can use the following command to show the 'align' of device dax.
+
+    ndctl list -X
+
+In order to get the proper 'align' of device dax, you need to install
+the library 'libdaxctl'.
 
 For example, device dax require the 2 MB alignment, so we can use
 following QEMU command line options to use it (/dev/dax0.0) as the
-- 
2.17.1