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>

2 files changed, 72 insertions, 16 deletions

diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index 7eb40faa9a3..73d58d853b2 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -2984,20 +2984,26 @@ dht_normalize_stats (struct statvfs *buf, unsigned long bsize,
 
 int
 dht_statfs_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                int op_ret, int op_errno, struct statvfs *statvfs, dict_t *xdata)
+                int op_ret, int op_errno, struct statvfs *statvfs,
+                dict_t *xdata)
 {
-        dht_local_t *local              = NULL;
-        int          this_call_cnt      = 0;
-        int          bsize              = 0;
-        int          frsize             = 0;
-        int8_t       quota_deem_statfs  = 0;
-        GF_UNUSED int     ret           = 0;
-        unsigned long     new_usage     = 0;
-        unsigned long     cur_usage     = 0;
 
-        ret = dict_get_int8 (xdata, "quota-deem-statfs", &quota_deem_statfs);
+        gf_boolean_t            event              = _gf_false;
+        qdstatfs_action_t       action             = qdstatfs_action_OFF;
+        dht_local_t *           local              = NULL;
+        int                     this_call_cnt      = 0;
+        int                     bsize              = 0;
+        int                     frsize             = 0;
+        GF_UNUSED int           ret                = 0;
+        unsigned long           new_usage          = 0;
+        unsigned long           cur_usage          = 0;
 
         local = frame->local;
+        GF_ASSERT (local);
+
+        if (xdata)
+                ret = dict_get_int8 (xdata, "quota-deem-statfs",
+                                     (int8_t *)&event);
 
         LOCK (&frame->lock);
         {
@@ -3012,13 +3018,51 @@ dht_statfs_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 }
                 local->op_ret = 0;
 
-                if (quota_deem_statfs) {
-                        new_usage = statvfs->f_blocks - statvfs->f_bfree;
-                        cur_usage = local->statvfs.f_blocks - local->statvfs.f_bfree;
-                        /* We take the maximux of the usage from the subvols */
-                        if (new_usage >= cur_usage)
+                switch (local->quota_deem_statfs) {
+                case _gf_true:
+                        if (event == _gf_true)
+                                action = qdstatfs_action_COMPARE;
+                        else
+                                action = qdstatfs_action_NEGLECT;
+                        break;
+
+                case _gf_false:
+                        if (event == _gf_true) {
+                                action = qdstatfs_action_REPLACE;
+                                local->quota_deem_statfs = _gf_true;
+                        }
+                        break;
+
+                default:
+                        gf_log (this->name, GF_LOG_ERROR, "Encountered third "
+                                "value for boolean variable %d",
+                                local->quota_deem_statfs);
+                        break;
+                }
+
+                if (local->quota_deem_statfs) {
+                        switch (action) {
+                        case qdstatfs_action_NEGLECT:
+                                goto unlock;
+
+                        case qdstatfs_action_REPLACE:
                                 local->statvfs = *statvfs;
-                        goto unlock;
+                                goto unlock;
+
+                        case qdstatfs_action_COMPARE:
+                                new_usage = statvfs->f_blocks -
+                                             statvfs->f_bfree;
+                                cur_usage = local->statvfs.f_blocks -
+                                             local->statvfs.f_bfree;
+
+                                /* Take the max of the usage from subvols */
+                                if (new_usage >= cur_usage)
+                                        local->statvfs = *statvfs;
+                                goto unlock;
+
+                        default:
+                                break;
+                        }
                 }
 
                 if (local->statvfs.f_bsize != 0) {
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;