Add configuration for upload purging

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>

docs/configuration.md

@@ -43,6 +43,12 @@ storage:
 		rootdirectory: /s3/object/name/prefix
 	cache:
 		layerinfo: inmemory
+	maintenance:
+		uploadpurging:
+			enabled: true
+			age: 168h
+			interval: 24h
+			dryrun: false
 auth:
 	silly:
 		realm: silly-realm
@@ -221,6 +227,12 @@ storage:
 		rootdirectory: /s3/object/name/prefix
 	cache:
 		layerinfo: inmemory
+	maintenance:
+		uploadpurging:
+			enabled: true
+			age: 168h
+			interval: 24h
+			dryrun: false
 ```
 
 The storage option is **required** and defines which storage backend is in use.
@@ -410,6 +422,27 @@ This storage backend uses Amazon's Simple Storage Service (S3).
   </tr> 
 </table>
 
+### Maintenance
+
+Currently the registry can perform one maintenance function: upload purging.  This and future
+maintenance functions which are related to storage can be configured under the maintenance section.
+
+### Upload Purging
+
+Upload purging is a background process that periodically removes orphaned files from the upload
+directories of the registry.  Upload purging is enabled by default.  To 
+ configure upload directory purging, the following parameters
+must be set.
+
+
+| Parameter | Required | Description
+  --------- | -------- | -----------
+`enabled` | yes | Set to true to enable upload purging.  Default=true. |
+`age` | yes | Upload directories which are older than this age will be deleted.  Default=168h (1 week)
+`interval` | yes | The interval between upload directory purging.  Default=24h.  
+`dryrun` | yes |  dryrun can be set to true to obtain a summary of what directories will be deleted.  Default=false.
+
+Note: `age` and `interval` are strings containing a number with optional fraction and a unit suffix: e.g. 45m, 2h10m, 168h (1 week).  
 
 ## auth
 
@@ -1139,7 +1172,8 @@ Configure the behavior of the Redis connection pool.
     </td>
   </tr>  
 </table>
- 
+
+
 ## Example: Development configuration
 
 The following is a simple example you can use for local development:

docs/deploying.md

@@ -205,6 +205,9 @@ storage:
       layerinfo: inmemory
   filesystem:
       rootdirectory: /tmp/registry-dev
+  maintenance:
+		uploadpurging:
+			enabled: false
 http:
   addr: :5000
   secret: asecretforlocaldevelopment