The RDMA QIOChannel does not support bi-directional communication, so when RDMA 
live migration with postcopy enabled, the source qemu return path get qemu file 
error.

These patches implement bi-directional communication for RDMA QIOChannel and 
disable the RDMA WRITE during the postcopy phase.

This patch just make postcopy works, and will improve performance later.

[v3]
 - add a mutex in QEMUFile struct to avoid concurrent channel close (Daniel)
 - destroy the mutex before free QEMUFile (David)
 - use rdmain and rmdaout instead of rdma->return_path (Daniel)

[v2]
 - does not update bytes_xfer when disable RDMA WRITE (David)
 - implement bi-directional communication for RDMA QIOChannel (Daniel)


Lidong Chen (6):
  migration: disable RDMA WRITE after postcopy started
  migration: create a dedicated connection for rdma return path
  migration: remove unnecessary variables len in QIOChannelRDMA
  migration: avoid concurrent invoke channel_close by different threads
  migration: implement bi-directional RDMA QIOChannel
  migration: Stop rdma yielding during incoming postcopy

 migration/colo.c         |   2 +
 migration/migration.c    |   2 +
 migration/postcopy-ram.c |   2 +
 migration/qemu-file.c    |  13 +-
 migration/ram.c          |   4 +
 migration/rdma.c         | 321 +++++++++++++++++++++++++++++++++++++++++------
 migration/savevm.c       |   3 +
 7 files changed, 307 insertions(+), 40 deletions(-)

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1.8.3.1