features/quota: Make dht_statfs_cbk more fool proof from quota_deem_statfs

Problem:
The function depends on the fact that if quota-deem-statfs option is enabled,
all of the subvolumes send their xdata with quota-deem-statfs flag ON. But,
this may not be true in case of errors in some of the subvolumes.

There is a decision/policy made which assumes quota-deem-statfs to be ON if at
least ONE of the subvolumes sends the flag ON. By this, df reports quota
modified statfs values if *at least ONE* of the bricks sends the
quota-deem-statfs flag ON. This can be visualized with the below "Transition
Diagram/State Machine".

        Event: Each Quota deem statfs status from the individual bricks
        Action: Decision taken on the calculation of the statvfs received
        State: Whether quota deem statfs is ON or OFF (0: OFF, 1: ON)
        Input: Event from individual bricks

              ___                  ___
             /   \   OFF*         /   \  (OFF|ON)*
            |     |              |     |
             \   /        ON      \   /
        -----> 0  ----------------> 1

The below Transition Function depicts the relation between the statfs
calculation based on the events received.

         State          Event          action
        -------------------------------------
          OFF            OFF            OFF
          OFF            ON            REPLACE
          ON             OFF           NEGLECT
          ON             ON            COMPARE

Change-Id: I0e8fb7d3945a3ca3dde0bb99de6cd397e27a3162
BUG: 1048786
Signed-off-by: Varun Shastry <vshastry@redhat.com>
Reviewed-on: http://review.gluster.org/6652
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Tested-by: Raghavendra G <rgowdapp@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/xlators/cluster/dht/src/dht-common.h b/xlators/cluster/dht/src/dht-common.h
index ba66306dd13..e45418a73f6 100644
--- a/xlators/cluster/dht/src/dht-common.h
+++ b/xlators/cluster/dht/src/dht-common.h
@@ -100,6 +100,17 @@ struct dht_rebalance_ {
         dict_t              *xdata;
 };
 
+/**
+ * Enum to store decided action based on the qdstatfs (quota-deem-statfs)
+ * events
+ **/
+typedef enum {
+        qdstatfs_action_OFF = 0,
+        qdstatfs_action_REPLACE,
+        qdstatfs_action_NEGLECT,
+        qdstatfs_action_COMPARE,
+} qdstatfs_action_t;
+
 struct dht_local {
         int                      call_cnt;
         loc_t                    loc;
@@ -187,6 +198,7 @@ struct dht_local {
         struct dht_rebalance_ rebalance;
         xlator_t        *first_up_subvol;
 
+        gf_boolean_t     quota_deem_statfs;
 };
 typedef struct dht_local dht_local_t;