dm cache: add policy name to status output

The cache's policy may have been established using the "default" alias,
which is currently the "mq" policy but the default policy may change in
the future.  It is useful to know exactly which policy is being used.

Add a 'real' member to the dm_cache_policy_type structure and have the
"default" dm_cache_policy_type point to the real "mq"
dm_cache_policy_type.  Update dm_cache_policy_get_name() to check if
real is set, if so report the name of the real policy (not the alias).

Requested-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt
index 63fd7cfa4cf1..e6b72d355151 100644
--- a/Documentation/device-mapper/cache.txt
+++ b/Documentation/device-mapper/cache.txt
@@ -221,7 +221,7 @@ Status
 <cache block size> <#used cache blocks>/<#total cache blocks>
 <#read hits> <#read misses> <#write hits> <#write misses>
 <#demotions> <#promotions> <#dirty> <#features> <features>*
-<#core args> <core args>* <#policy args> <policy args>*
+<#core args> <core args>* <policy name> <#policy args> <policy args>*
 
 metadata block size      : Fixed block size for each metadata block in
                              sectors
@@ -250,6 +250,7 @@ feature args		 : 'writethrough' (optional)
 #core args               : Number of core arguments (must be even)
 core args                : Key/value pairs for tuning the core
                              e.g. migration_threshold
+policy name              : Name of the policy
 #policy args             : Number of policy arguments to follow (must be even)
 policy args              : Key/value pairs
                              e.g. sequential_threshold