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    • Hoang Huu Le's avatar
      tipc: update a binding service via broadcast · cad2929d
      Hoang Huu Le authored
      
      
      Currently, updating binding table (add service binding to
      name table/withdraw a service binding) is being sent over replicast.
      However, if we are scaling up clusters to > 100 nodes/containers this
      method is less affection because of looping through nodes in a cluster one
      by one.
      
      It is worth to use broadcast to update a binding service. This way, the
      binding table can be updated on all peer nodes in one shot.
      
      Broadcast is used when all peer nodes, as indicated by a new capability
      flag TIPC_NAMED_BCAST, support reception of this message type.
      
      Four problems need to be considered when introducing this feature.
      1) When establishing a link to a new peer node we still update this by a
      unicast 'bulk' update. This may lead to race conditions, where a later
      broadcast publication/withdrawal bypass the 'bulk', resulting in
      disordered publications, or even that a withdrawal may arrive before the
      corresponding publication. We solve this by adding an 'is_last_bulk' bit
      in the last bulk messages so that it can be distinguished from all other
      messages. Only when this message has arrived do we open up for reception
      of broadcast publications/withdrawals.
      
      2) When a first legacy node is added to the cluster all distribution
      will switch over to use the legacy 'replicast' method, while the
      opposite happens when the last legacy node leaves the cluster. This
      entails another risk of message disordering that has to be handled. We
      solve this by adding a sequence number to the broadcast/replicast
      messages, so that disordering can be discovered and corrected. Note
      however that we don't need to consider potential message loss or
      duplication at this protocol level.
      
      3) Bulk messages don't contain any sequence numbers, and will always
      arrive in order. Hence we must exempt those from the sequence number
      control and deliver them unconditionally. We solve this by adding a new
      'is_bulk' bit in those messages so that they can be recognized.
      
      4) Legacy messages, which don't contain any new bits or sequence
      numbers, but neither can arrive out of order, also need to be exempt
      from the initial synchronization and sequence number check, and
      delivered unconditionally. Therefore, we add another 'is_not_legacy' bit
      to all new messages so that those can be distinguished from legacy
      messages and the latter delivered directly.
      
      v1->v2:
       - fix warning issue reported by kbuild test robot <lkp@intel.com>
       - add santiy check to drop the publication message with a sequence
      number that is lower than the agreed synch point
      
      Signed-off-by: default avatarkernel test robot <lkp@intel.com>
      Signed-off-by: default avatarHoang Huu Le <hoang.h.le@dektech.com.au>
      Acked-by: default avatarJon Maloy <jmaloy@redhat.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      cad2929d