cluster/dht: avoid overwriting client writes during migration

For more details on this issue see
https://github.com/gluster/glusterfs/issues/308

Solution:
This is a restrictive solution where a file will not be migrated
if a client writes to it during the migration. This does not
check if the writes from the rebalance and the client actually
do overlap.

If dht_writev_cbk finds that the file is being migrated (PHASE1)
it will set an xattr on the destination file indicating the file
was updated by a non-rebalance client.
Rebalance checks if any other client has written to the dst file
and aborts the file migration if it finds the xattr.

updates gluster/glusterfs#308

Change-Id: I73aec28bc9dbb8da57c7425ec88c6b6af0fbc9dd
Signed-off-by: Susant Palai <spalai@redhat.com>
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Signed-off-by: N Balachandran <nbalacha@redhat.com>

1 files changed, 27 insertions, 1 deletions

diff --git a/xlators/cluster/dht/src/dht-inode-write.c b/xlators/cluster/dht/src/dht-inode-write.c
index 7c596b1c099..226ee95e8b3 100644
--- a/xlators/cluster/dht/src/dht-inode-write.c
+++ b/xlators/cluster/dht/src/dht-inode-write.c
@@ -95,6 +95,33 @@ dht_writev_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 
         /* Check if the rebalance phase1 is true */
         if (IS_DHT_MIGRATION_PHASE1 (postbuf)) {
+                if (!dht_is_tier_xlator (this)) {
+                        if (!local->xattr_req) {
+                                local->xattr_req = dict_new ();
+                                if (!local->xattr_req) {
+                                        gf_msg (this->name, GF_LOG_ERROR,
+                                                DHT_MSG_NO_MEMORY,
+                                                ENOMEM, "insufficient memory");
+                                        local->op_errno = ENOMEM;
+                                        local->op_ret = -1;
+                                        goto out;
+                                }
+                        }
+
+                        ret = dict_set_uint32 (local->xattr_req,
+                                               GF_PROTECT_FROM_EXTERNAL_WRITES,
+                                               1);
+                        if (ret) {
+                                gf_msg (this->name, GF_LOG_ERROR,
+                                        DHT_MSG_DICT_SET_FAILED, 0,
+                                        "Failed to set key %s in dictionary",
+                                        GF_PROTECT_FROM_EXTERNAL_WRITES);
+                                local->op_errno = ENOMEM;
+                                local->op_ret = -1;
+                                goto out;
+                        }
+                }
+
                 dht_iatt_merge (this, &local->stbuf, postbuf, NULL);
                 dht_iatt_merge (this, &local->prebuf, prebuf, NULL);
 
@@ -146,7 +173,6 @@ dht_writev2 (xlator_t *this, xlator_t *subvol, call_frame_t *frame, int ret)
                 return 0;
         }
 
-
         if (subvol == NULL)
                 goto out;