dm cache: add block sizes and total cache blocks to status output

Improve cache_status to emit:
<metadata block size> <#used metadata blocks>/<#total metadata blocks>
<cache block size> <#used cache blocks>/<#total cache blocks>
...

Adding the block sizes allows for easier calculation of the overall size
of both the metadata and cache devices.  Adding <#total cache blocks>
provides useful context for how much of the cache is used.

Unfortunately these additions to the status will require updates to
users' scripts that monitor the cache status.  But these changes help
provide more comprehensive information about the cache device and will
simplify tools that are being developed to manage dm-cache devices --
because they won't need to issue 3 operations to cobble together the
information that we can easily provide via a single status ioctl.

While updating the status documentation in cache.txt spaces were
tabify'd.

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

1 files changed, 28 insertions, 22 deletions

diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt
index 719320b5ed3f..63fd7cfa4cf1 100644
--- a/Documentation/device-mapper/cache.txt
+++ b/Documentation/device-mapper/cache.txt
@@ -217,36 +217,42 @@ the characteristics of a specific policy, always request it by name.
 Status
 ------
 
-<#used metadata blocks>/<#total metadata blocks> <#read hits> <#read misses>
-<#write hits> <#write misses> <#demotions> <#promotions> <#blocks in cache>
-<#dirty> <#features> <features>* <#core args> <core args>* <#policy args>
-<policy args>*
-
-#used metadata blocks    : Number of metadata blocks used
-#total metadata blocks   : Total number of metadata blocks
-#read hits               : Number of times a READ bio has been mapped
+<metadata block size> <#used metadata blocks>/<#total metadata blocks>
+<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>*
+
+metadata block size      : Fixed block size for each metadata block in
+                             sectors
+#used metadata blocks    : Number of metadata blocks used
+#total metadata blocks   : Total number of metadata blocks
+cache block size         : Configurable block size for the cache device
+                             in sectors
+#used cache blocks       : Number of blocks resident in the cache
+#total cache blocks      : Total number of cache blocks
+#read hits               : Number of times a READ bio has been mapped
                              to the cache
-#read misses             : Number of times a READ bio has been mapped
+#read misses             : Number of times a READ bio has been mapped
                              to the origin
-#write hits              : Number of times a WRITE bio has been mapped
+#write hits              : Number of times a WRITE bio has been mapped
                              to the cache
-#write misses            : Number of times a WRITE bio has been
+#write misses            : Number of times a WRITE bio has been
                              mapped to the origin
-#demotions               : Number of times a block has been removed
+#demotions               : Number of times a block has been removed
                              from the cache
-#promotions              : Number of times a block has been moved to
+#promotions              : Number of times a block has been moved to
                              the cache
-#blocks in cache         : Number of blocks resident in the cache
-#dirty                   : Number of blocks in the cache that differ
+#dirty                   : Number of blocks in the cache that differ
                              from the origin
-#feature args            : Number of feature args to follow
-feature args             : 'writethrough' (optional)
-#core args               : Number of core arguments (must be even)
-core args                : Key/value pairs for tuning the core
+#feature args            : Number of feature args to follow
+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 args             : Number of policy arguments to follow (must be even)
-policy args              : Key/value pairs
-                             e.g. 'sequential_threshold 1024
+#policy args             : Number of policy arguments to follow (must be even)
+policy args              : Key/value pairs
+                             e.g. sequential_threshold
 
 Messages
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