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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@7046 d57e44dd-8a1f-0410-8b47-8ef2f437770f
45 lines
2.6 KiB
Plaintext
45 lines
2.6 KiB
Plaintext
ib_srpt and session management
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==============================
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The following actions related to SRP sessions can all occur concurrently:
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* The communication manager invokes either srpt_ib_cm_handler() or
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srpt_rdma_cm_handler().
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* HCA driver invokes the queue pair (QP) completion handler srpt_completion().
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* HCA driver invokes the QP async event handler srpt_qp_event().
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* HCA transfers data between initiator and target via RDMA.
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* srpt_compl_thread() polls the QP.
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* SCST core invokes one of the callback functions defined in srpt_template.
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The actions that occur over the lifetime of a session are as follows:
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- A REQ message is received from the initiator.
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- srpt_cm_req_recv() is invoked, allocates a queue pair and creates a
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completion thread.
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- If the connection request is not accepted, a REJ message is sent and
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srpt_close_ch() is invoked. The srpt_close_ch() call causes the completion
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thread to stop and the allocated resources to be freed asynchronously.
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- If the connection request is accepted a REP message is sent to the initiator.
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- Once an RTU message is received from the initiator, srpt_cm_rtu_recv() is
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invoked. That function changes the queue pair state into RTS, the channel
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state into CH_LIVE and wakes up the completion thread.
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- RDMA communication starts and continues until either a DREQ message is
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received or sent. A DREQ is sent either because a target port is disabled or
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from inside the srpt_close_session() function.
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- After a DREQ has been sent either a DREP will be received
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(srpt_cm_drep_recv()) or the TimeWait state will be reached and will be left
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(srpt_cm_timewait_exit()).
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- srpt_cm_drep_recv() and srpt_cm_timewait_exit() invoke srpt_close_ch().
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- srpt_close_ch() changes the channel state into CH_DISCONNECTING, the
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queue pair state into IB_QPS_ERR and queues a zero-length write.
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- Upon receipt of the zero-length write completion the channel state is
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changed into CH_DISCONNECTED. This is the last work completion so once the
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channel state has reached CH_DISCONNECTED it is guaranteed that the queue
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pair completion handler won't be invoked again and also that the completion
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handler won't call wake_up_process(ch->thread) anymore.
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- That channel state change causes the polling loop in the completion thread
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to stop and also triggers a call of scst_unregister_session().
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- Once scst_unregister_session() has finished srpt_unreg_sess() is invoked.
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- srpt_unreg_sess() destroys the CM ID and decrements the channel refcount.
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- Once the channel refcount drops to zero srpt_free_ch() is invoked which
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frees the queue pair and other IB resources.
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