cluster/afr: Enforce order in pre/post op

The xattrop order in pre/post op on all the subvols
is client-0, client-1... client-n where n is (replica-count - 1).
This order can lead to invalid split-brains if the brick
dies in the middle of xattrops.

Example: transaction completed pre-op, so on all the subvolumes
xattrs have '1' changelog. Now post-op is sent to both the subvols.
On subvol-0 change-log of client-0 is decremented to 0, before
decrementing change-log of client-1 to 0 the brick dies.
This change-log status on subvol-0 gives the meaning that a
change is done on subvol-0 successfully but on subvol-1 it failed.
Which is not what happened.
Changes done when the subvol-0 was down will lead to pending
change-log on subvol-1 for subvol-0. Which is correct.
When the subvol-0 is brought back up, the change-log will be in
split-brain state even when it is not a legitimate split-brain.

If the brick dies in the middle of xattrops it should remain fool.
Pre-op should perform xattrop of the local change-log first and
post-op should perform xattrop of the local change-log last.
In case of optimistic changelogs txn_changelog should be done
last on local if it succeeds, first if it fails.

Change-Id: Ib6eeb20cdc49b0b1fd2f454f25a9c8e08388c6e7
BUG: 765194
Signed-off-by: Pranith Kumar K <pranithk@gluster.com>
Reviewed-on: http://review.gluster.com/3226
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 1 insertions, 6 deletions

diff --git a/xlators/cluster/afr/src/afr.h b/xlators/cluster/afr/src/afr.h
index dfad29de..27cb83a5 100644
--- a/xlators/cluster/afr/src/afr.h
+++ b/xlators/cluster/afr/src/afr.h
@@ -670,12 +670,7 @@ typedef struct _afr_local {
 
                 afr_transaction_type type;
 
-                int success_count;
-                int erase_pending;
-                int failure_count;
-
-                int last_tried;
-                int32_t *child_errno;
+                int32_t         **txn_changelog;//changelog after pre+post ops
                 unsigned char   *pre_op;
 
                 call_frame_t *main_frame;