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, 9 insertions, 0 deletions

diff --git a/xlators/storage/posix/src/posix-inode-fd-ops.c b/xlators/storage/posix/src/posix-inode-fd-ops.c
index c90bc6c438a..812cf792874 100644
--- a/xlators/storage/posix/src/posix-inode-fd-ops.c
+++ b/xlators/storage/posix/src/posix-inode-fd-ops.c
@@ -1579,6 +1579,15 @@ posix_writev (call_frame_t *frame, xlator_t *this, fd_t *fd,
 
         _fd = pfd->fd;
 
+        ret = posix_check_internal_writes (this, fd, _fd, xdata);
+        if (ret < 0) {
+                gf_msg (this->name, GF_LOG_ERROR, 0, 0,
+                        "possible overwrite from internal client, fd=%p", fd);
+                op_ret = -1;
+                op_errno = EBUSY;
+                goto out;
+        }
+
         if (xdata) {
                 if (dict_get (xdata, GLUSTERFS_WRITE_IS_APPEND))
                         write_append = _gf_true;