Re: [PATCHv2] scsi: disable automatic target scan

[Steffen Maier <maier@linux.vnet.ibm.com>]

On 03/15/2016 12:28 PM, Hannes Reinecke wrote:
> On 03/15/2016 12:03 PM, Steffen Maier wrote:
>> On 03/15/2016 08:19 AM, Hannes Reinecke wrote:
>>> On larger installations it is useful to disable automatic LUN
>>> scanning, and only add the required LUNs via udev rules.
>>> This can speed up bootup dramatically.
>>>
>>> This patch introduces a new scan module parameter value 'manual',
>>> which works like 'none', but can be overriden by setting the 'rescan'
>>> value from scsi_scan_target to 'SCSI_SCAN_MANUAL'.
>>> And it updates all relevant callers to set the 'rescan' value
>>> to 'SCSI_SCAN_MANUAL' if invoked via the 'scan' option in sysfs.
>>>
>>> Signed-off-by: Hannes Reinecke <hare@suse.de>

>> In particular, the following might be necessary in order not to
>> break zfcp manual LUN addition (as long as zfcp still has its own
>> unit_add sysfs interface; completely replacing it with the solution
>> here is not easy because it breaks the zfcp sysfs user interface):
>>
>>> void zfcp_unit_scsi_scan(struct zfcp_unit *unit)
>>> {
>>>      struct fc_rport *rport = unit->port->rport;
>>>      u64 lun;
>>>
>>>      lun = scsilun_to_int((struct scsi_lun *) &unit->fcp_lun);
>>>
>>>      if (rport && rport->port_state == FC_PORTSTATE_ONLINE)
>>> -         scsi_scan_target(&rport->dev, 0, rport->scsi_target_id,
>>> lun, 1);
>>> +         scsi_scan_target(&rport->dev, 0, rport->scsi_target_id,
>>> lun,
>>> +                  SCSI_SCAN_MANUAL);
>>> }

> As for zfcp: it also relies on the 'user_scan' callback from
> scsi_transport_fc, so it will fall under the same rules as any
> 'normal' FC HBA.

I'm not sure, since zfcp needs to continue to support HBA hardware 
virtualization without NPIV.

The zfcp unit_add sysfs interface is kind of a peer of your common code 
scsi scan interface interface. I think, for zfcp users, a unit_add needs 
to be sufficient. It would be strange to additionally have them also 
write the same LUN into the Scsi_Host's scan sysfs attribute, i.e. 
having to double configure things.

> But I do think we can tie the 'scan' module parameter with the
> 'allow_lun_scan' parameter from zfcp; both are now doing essentially
> the same. Eg the 'allow_lun_scan' parameter could take it's default
> value from the 'scan' parameter.

> In the long run we might want to check if and how the global 'scan'
> parameter can be moved down to a host parameter, which then would
> eliminate the need for a zfcp-specific parameter.

I need to think about this.

-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

Linux on z Systems Development

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