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[Qemu-devel] libiscsi task cancellation

From: Stefan Hajnoczi
Subject: [Qemu-devel] libiscsi task cancellation
Date: Thu, 8 Feb 2018 14:08:02 +0000

SAM-5, 5.6 Aborting commands says:

  A command is aborted when a SCSI device condition (see 6.3), command,
  or task management function causes termination of the command prior to
  its completion by the device server. After a command is aborted and
  TASK ABORTED status, if any, is returned, the SCSI target device shall
  send no further requests or responses for that command.

Then "Table 48 — Task management functions that abort commands (part 1
of 2)" goes on to say that no TASK ABORTED status is returned for
aborted commands "if the ABORT TASK scope is I_T_L nexus".

My interpretation is that the target doesn't have to send a response
for the aborted command.  It just needs to complete the ABORT TASK
TMF.  Afterwards the initiator knows the task is gone and will receive
no more responses.

Is my understanding correct?

Now on to libiscsi:

The iscsi_task_mgmt_async() API documentation says:

  * abort_task will also cancel the scsi task. The callback for the
scsi task will be invoked with

I see that the ABORT TASK TMF response invokes the user's
iscsi_task_mgmt_async() callback but not the command callback.  I'm
not sure how the command callback is invoked with
SCSI_STATUS_CANCELLED unless libiscsi is relying on the target to send
that response.

Is libiscsi honoring its iscsi_task_mgmt_async() contract?


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