Re: [Qemu-devel] libiscsi task cancellation

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Feb 8, 2018 at 2:58 PM, Hannes Reinecke <hare@suse.de> 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
> FUNCTION COMPLETE, too.
>
> 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.

Stefan