dht/remove-brick: Avoid data loss for hard link migration

Problem: If the hashed subvol of a file has reached cluster.min-free-disk,
for a create opertaion a linkto file will be created on the hashed and
the data file will be created on some other brick.

For creation of the linkfile we populate the dictionary with linkto key
and value as the cached subvol. After successful linkto file creation,
the linkto-key-value pair is not deleted form the dictionary and hence,
the data file will also have linkto xattr which points to itself.This looks
something like this.

  client-0                                    client-1
-------T file                               rwx------file
linkto.xattr=client-1                       linkto.xattr=client-1

Now coming to the data loss part. Hardlink migration highly depend on this
linkto xattr on the data file. This value should be the new hashed subvol
of the first hardlink encountered post fix-layout. But when it tries to
read the linkto xattr it gets the same target as where it is sitting.

Now the source and destination are same for migration. At the end of
migration the source file is truncated and deleted, which in this case
is the destination and also the only data file it self resulting in
data loss.

Change-Id: I36b1d105752bd9467757ecf3f103b45c666783d6
BUG: 1260051
Signed-off-by: Susant Palai <spalai@redhat.com>
Reviewed-on: http://review.gluster.org/12105
Reviewed-by: N Balachandran <nbalacha@redhat.com>
Tested-by: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>

0 files changed, 0 insertions, 0 deletions