dht, md-cache, upcall: Add invalidation of IATT when the layout changes

Issue:
dht_layout is built as a part of lookup only. The layout can be
modified by rebalance process. Since every IO fop is preceded
by a lookup, there are very less issues of stale layout. But
with enhancements of aggressive caching of stats in md-cache,
the lookup will reduce and expose the stale layout issue often.

Solution:
Since stale layout is already an issue on dht, there is already
a plan to fix this at the dht layer, but this fix is not currently
planned for any release. Until this fix comes out, we can have
a workaround where, the upcall will send a notification to md-cache
when a layout xattr is changed. As a part of layout change notification
the existing cache is invalidated and the next lookup will fetch the
latest layout.

This is not a foolproof solution as the window between the layout change
and the next lookup(after invalidation of stat), where there will be stale
layout. But until the final fix comes in, this reduces the stale layout
window.

Change-Id: Iacf871a38b35880c1fc0bc68fe7ce291265e71d4
BUG: 1369638
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/15300
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>

0 files changed, 0 insertions, 0 deletions