[Sheepdog] [PATCH v5]introduce SD_STATUS_HALT to stop serving IO

[Liu Yuan]

This patch set introduce a new cluster status into sheepdog, which is supposed
to prevent sheepdog from serving IO when lack of redundant nodes.

Changes from v4 to v5 are:

 - rebased on the msater branch
 - add get/set_cluster_flags()
 - revert hdr flags into uint16_t
 - use Macro in set_nohalt()

Changes from v3 to v4 are:

 - change hdr flags into uint32_t from uint16_t

Changes from v2 to v3 are:

 - add a new flag field in struct cluster_info and NOHALT uses one bit of it.
 - use hdr.flags to set the nohalt option in collie.
 - add a new epoch_log_read_nr() to return # of the entries instead of bytes.

Changes from v1 to v2 are:

 - refactor's get_cluster_status() to prepare the code for change.
 - address Kazutaka's comments.
 - make cluster 'halt' optionally.

Liu Yuan (7):
      sheep: add a helper epoch_log_read_nr()
      sheep: refactor get_cluster_status()
      sheep: remove wrong 'unknown message' in the log
      sheep: introduce SD_STATUS_HALT
      sheep: add a helper function to get nr_zones
      sheep: add set/get_cluster_status()
      sheep: use SD_STATUS_HALT to stop serving IO

 collie/cluster.c         |   14 +++-
 collie/collie.c          |    1 +
 include/sheep.h          |    3 +
 include/sheepdog_proto.h |    1 +
 sheep/group.c            |  228 +++++++++++++++++++++++++++++-----------------
 sheep/sheep_priv.h       |    7 ++
 sheep/store.c            |   46 +++++++++
 7 files changed, 214 insertions(+), 86 deletions(-)

Thanks,
Yuan