cluster/afr: add a new option to select read-subvol by index

read subvolume is a nice option to set prefred read child if you have a
replication over 2 datacenter.  if you have 2 datacenter and have a
distributed replication where one set of servers are in datacenter one
and the other (the replicated) are in the other datacenter
read-subvolume it not very handy since it goes over name and the
subvolume name is different for each replication pair.  i added a new
option called read-subvolume-index which take the number of the
subvolume to choose.  0 fo first , 1 for second and so on subvolume in
every replication.  this option can now be used in the --xlator-option
mount option to choose the prefered read child for all replication at
once.  For Example on all clients in datacenter one you can use
--xlator-option=volumename-replication-*.read-subvolume-index=0 to
prefer read from the servers in datacenter one.  when you expand or
shrink the volume no changes are needed to the client config since the
wildcard will set this option automatic on reconfigure.

Change-Id: I3b47432f77037c380ff4a6296636c6f8fc953db9
BUG: 837420
Original-author: domwo <glusterfs@wollina.de>
Signed-off-by: domwo <glusterfs@wollina.de>
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.com/3615
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/xlators/cluster/afr/src/afr.c b/xlators/cluster/afr/src/afr.c
index ebb9f1ee904..cd84c357da8 100644
--- a/xlators/cluster/afr/src/afr.c
+++ b/xlators/cluster/afr/src/afr.c
@@ -107,6 +107,7 @@ reconfigure (xlator_t *this, dict_t *options)
 {
         afr_private_t *priv        = NULL;
         xlator_t      *read_subvol = NULL;
+        int            read_subvol_index = -1;
         int            ret         = -1;
         int            index       = -1;
         char          *qtype       = NULL;
@@ -162,6 +163,18 @@ reconfigure (xlator_t *this, dict_t *options)
                 priv->read_child = index;
         }
 
+        GF_OPTION_RECONF ("read-subvolume-index",read_subvol_index, options,int32,out);
+
+        if (read_subvol_index >-1) {
+                index=read_subvol_index;
+                if (index >= priv->child_count) {
+                        gf_log (this->name, GF_LOG_ERROR, "%d not a subvolume-index",
+                                index);
+                        goto out;
+                }
+                priv->read_child = index;
+        }
+
         GF_OPTION_RECONF ("eager-lock", priv->eager_lock, options, bool, out);
         GF_OPTION_RECONF ("quorum-type", qtype, options, str, out);
         GF_OPTION_RECONF ("quorum-count", priv->quorum_count, options,
@@ -199,6 +212,7 @@ init (xlator_t *this)
         int            ret         = -1;
         GF_UNUSED int  op_errno    = 0;
         xlator_t      *read_subvol = NULL;
+        int            read_subvol_index = -1;
         xlator_t      *fav_child   = NULL;
         char          *qtype       = NULL;
 
@@ -241,6 +255,15 @@ init (xlator_t *this)
                         goto out;
                 }
         }
+        GF_OPTION_INIT ("read-subvolume-index",read_subvol_index,int32,out);
+        if (read_subvol_index > -1) {
+                if (read_subvol_index >= priv->child_count) {
+                        gf_log (this->name, GF_LOG_ERROR, "%d not a subvolume-index",
+                                read_subvol_index);
+                        goto out;
+                }
+                priv->read_child = read_subvol_index;
+        }
         GF_OPTION_INIT ("choose-local", priv->choose_local, bool, out);
 
         GF_OPTION_INIT ("read-hash-mode", priv->hash_mode, uint32, out);
@@ -502,6 +525,10 @@ struct volume_options options[] = {
         { .key  = {"read-subvolume" },
           .type = GF_OPTION_TYPE_XLATOR
         },
+        { .key  = {"read-subvolume-index" },
+          .type = GF_OPTION_TYPE_INT,
+          .default_value = "-1",
+        },
         { .key = {"read-hash-mode" },
           .type = GF_OPTION_TYPE_INT,
           .min = 0,