afr,dht,ec: Replace GF_EVENT_CHILD_MODIFIED with event SOME_DESCENDENT_DOWN/UP

Backport of http://review.gluster.org/#/c/15764/

Currently these are few events related to child_up/down:
GF_EVENT_CHILD_UP :  Issued when any of the protocol client
connects.
GF_EVENT_CHILD_MODIFIED : Issued by afr/dht/ec
GF_EVENT_CHILD_DOWN : Issued when any of the protocol client
disconnects.
These events get modified at the dht/afr/ec layers. Here is a
brief on the same.

DHT:
- All the subvolumes reported once, and atleast one child came
  up, then GF_EVENT_CHILD_UP is issued
- connect GF_EVENT_CHILD_UP is issued
- disconnect GF_EVENT_CHILD_MODIFIED is issued
- All the subvolumes disconnected, GF_EVENT_CHILD_DOWN is issued

AFR:
- First subvolume came up, then GF_EVENT_CHILD_UP is issued
- Subsequent subvolumes coming up, results in GF_EVENT_CHILD_MODIFIED
- Any of the subvolumes go down, then GF_EVENT_SOME_CHILD_DOWN is issued
- Last up subvolume goes down, then GF_EVENT_CHILD_DOWN is issued

Until the patch [1] introduced GF_EVENT_SOME_CHILD_UP,
GF_EVENT_CHILD_MODIFIED was issued by afr/dht when any of the subvolumes
go up or down.

Now with md-cache changes, there is a necessity to differentiate between
child up and down. Hence, introducing GF_EVENT_SOME_DESCENDENT_DOWN/UP and
getting rid of GF_EVENT_CHILD_MODIFIED.

[1] http://review.gluster.org/12573

>Reviewed-on: http://review.gluster.org/15764
>CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
>NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
>Smoke: Gluster Build System <jenkins@build.gluster.org>
>Reviewed-by: N Balachandran <nbalacha@redhat.com>
>Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com> 
>Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
(cherry picked from commit f7ab6c45963fa0da68acedfb14281cd2456abc68)

Change-Id: I704140b6598f7ec705493251d2dbc4191c965a58
BUG: 1396880
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/15890
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/xlators/nfs/server/src/nfs.c b/xlators/nfs/server/src/nfs.c
index ddfa89dab11..3e7199c036d 100644
--- a/xlators/nfs/server/src/nfs.c
+++ b/xlators/nfs/server/src/nfs.c
@@ -1542,7 +1542,8 @@ notify (xlator_t *this, int32_t event, void *data, ...)
                 nfs_startup_subvolume (this, subvol);
                 break;
 
-        case GF_EVENT_CHILD_MODIFIED:
+        case GF_EVENT_SOME_DESCENDENT_DOWN:
+        case GF_EVENT_SOME_DESCENDENT_UP:
                 priv = this->private;
                 ++(priv->generation);
                 break;