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https://github.com/SCST-project/scst.git
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Gleb Chesnokov
b836a17e35
The SRPT guides mix current RDMA/CM code with Linux 2.6, procfs and OFED 1.5 procedures. Their parameter defaults, session names and tuning advice no longer describe the driver built by this tree. Commit020ec68ddc("ib_srpt: Change default behavior from using SRQ to not using SRQ") changed receive queues, and commit434207ab53("ib_srpt: Restore immediate data support") changed request sizing. Commitfa58faf95b("ib_srpt: Add RDMA/CM support") added the IP-based session naming mode. Commit08e532715d("Remove procfs support") invalidated the in-tree setup, while commitd6fd03107f("Split Makefiles: move kernel build rules into Kbuild files") moved the fault-injection flag. Commitc2bd2e8bf5("ib_srpt: Remove "thread" kernel module parameter and keep thread=1 behavior - the other two modes could cause soft lockup complaints") made threaded completion unconditional. Use ib_srpt.c, ib_srpt.h and conftests for current behavior. Scope SCSI multiqueue advice after Linux commit f664a3cc17b7 ("scsi: kill off the legacy IO path"), and mark OFED, HA, benchmark and test recipes as historical or destructive.
40 lines
2.3 KiB
Plaintext
40 lines
2.3 KiB
Plaintext
ib_srpt and session management
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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_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_do_compl_work() 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 an I/O context ring and a queue pair
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and creates an SCST session.
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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 allocated
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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 triggers processing of the wait list.
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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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because the SCST core requested to close the session.
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- After a DREQ has been sent either a DREP will be received or the TimeWait
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state will be reached. Both trigger a srpt_close_ch() call.
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- srpt_close_ch() changes the channel state into CH_DRAINING, 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.
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- scst_unregister_session() is called.
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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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