[PATCH 6/5] x86/intel_rdt: Add documentation for "info/last_cmd_status"

["Luck, Tony" <tony.luck@intel.com>]

From: Tony Luck <tony.luck@intel.com>

New file in the "info" directory helps diagnose what went wrong
when using the /sys/fs/resctrl file system

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
Oops ... forgot the Documentation ... here it is.

 Documentation/x86/intel_rdt_ui.txt | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/x86/intel_rdt_ui.txt b/Documentation/x86/intel_rdt_ui.txt
index 4d8848e4e224..6851854cf69d 100644
--- a/Documentation/x86/intel_rdt_ui.txt
+++ b/Documentation/x86/intel_rdt_ui.txt
@@ -87,6 +87,17 @@ with the following files:
 			bytes) at which a previously used LLC_occupancy
 			counter can be considered for re-use.
 
+Finally, in the top level of the "info" directory there is a file
+named "last_cmd_status". This is reset with every "command" issued
+via the file system (making new directories or writing to any of the
+control files). If the command was successful, it will read as "ok".
+If the command failed, it will provide more information that can be
+conveyed in the error returns from file operations. E.g.
+
+	# echo L3:0=f7 > schemata
+	bash: echo: write error: Invalid argument
+	# cat info/last_cmd_status
+	mask f7 has non-consecutive 1-bits
 
 Resource alloc and monitor groups
 ---------------------------------
-- 
2.11.0