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Re: [Qemu-devel] libiscsi task cancellation

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] libiscsi task cancellation
Date: Thu, 8 Feb 2018 15:12:15 +0000

On Thu, Feb 8, 2018 at 2:58 PM, Hannes Reinecke <address@hidden> wrote:
> On 02/08/2018 03:14 PM, Paolo Bonzini wrote:
>> On 08/02/2018 15:08, Stefan Hajnoczi wrote:
>>> 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
>>>   *            SCSI_STATUS_CANCELLED
>>> 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?
>> No, and QEMU is assuming the "wrong" behavior:
>> static void
>> iscsi_abort_task_cb(struct iscsi_context *iscsi, int status, void 
>> *command_data,
>>                     void *private_data)
>> {
>>     IscsiAIOCB *acb = private_data;
>>     acb->status = -ECANCELED;
>>     iscsi_schedule_bh(acb);
>> }
> The definition of ABORT TASK TMF in SAM is pretty much useless.
> To quote:
> A response of FUNCTION COMPLETE shall indicate that the task was aborted
> or was not in the task set.
> IE we have no idea if we ever managed to abort the task; if the task had
> been in-flight by the time we've send the TMF we'll be getting a
> So most FC HBA firmware implement the abort task with just a blacklist;
> the TMF will be returned immediately and the command response will be
> dropped if and when is arrives.

Great, thanks for confirming.


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