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, 17 insertions, 0 deletions

diff --git a/xlators/cluster/dht/src/dht-shared.c b/xlators/cluster/dht/src/dht-shared.c
index 8c011f72530..51c9d9cb3cf 100644
--- a/xlators/cluster/dht/src/dht-shared.c
+++ b/xlators/cluster/dht/src/dht-shared.c
@@ -524,6 +524,10 @@ dht_reconfigure (xlator_t *this, dict_t *options)
         GF_OPTION_RECONF ("lock-migration", conf->lock_migration_enabled,
                           options, bool, out);
 
+        GF_OPTION_RECONF ("force-migration", conf->force_migration,
+                          options, bool, out);
+
+
         if (conf->defrag) {
                 if (dict_get_str (options, "rebal-throttle", &temp_str) == 0) {
                         ret = dht_configure_throttle (this, conf, temp_str);
@@ -810,6 +814,10 @@ dht_init (xlator_t *this)
         GF_OPTION_INIT ("lock-migration", conf->lock_migration_enabled,
                          bool, err);
 
+        GF_OPTION_INIT ("force-migration", conf->force_migration,
+                        bool, err);
+
+
         if (defrag) {
               defrag->lock_migration_enabled = conf->lock_migration_enabled;
 
@@ -1203,5 +1211,14 @@ struct volume_options options[] = {
           .flags = OPT_FLAG_CLIENT_OPT | OPT_FLAG_SETTABLE | OPT_FLAG_DOC
         },
 
+        { .key =  {"force-migration"},
+          .type = GF_OPTION_TYPE_BOOL,
+          .default_value = "off",
+          .description = "If disabled, rebalance will not migrate files that "
+                         "are being written to by an application",
+          .op_version  = {GD_OP_VERSION_4_0_0},
+          .flags = OPT_FLAG_CLIENT_OPT | OPT_FLAG_SETTABLE | OPT_FLAG_DOC
+        },
+
         { .key  = {NULL} },
 };