linux-kernel - Re: [PATCH v4 3/3] ibmvscsi: Allow to configure maximum LUN

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Date:	Mon, 09 Nov 2015 16:05:53 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Laurent Vivier <lvivier@...hat.com>
CC:	martin.petersen@...cle.com, brking@...ux.vnet.ibm.com,
	tyreld@...ux.vnet.ibm.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] ibmvscsi: Allow to configure maximum LUN

On 11/09/2015 03:59 PM, Laurent Vivier wrote:
> 
> 
> On 09/11/2015 15:50, Hannes Reinecke wrote:
>> On 11/09/2015 03:47 PM, Laurent Vivier wrote:
>>> This patch allows to define the maximum LUN numbers.
>>> As defined in 4.6.9 of SAM-4, the encoding of LUN is
>>> on 5 bits (max_lun=32) and the current value is only 8.
>>>
>>> Signed-off-by: Laurent Vivier <lvivier@...hat.com>
>>> ---
>>>  drivers/scsi/ibmvscsi/ibmvscsi.c | 9 ++++++++-
>>>  drivers/scsi/ibmvscsi/ibmvscsi.h | 1 +
>>>  2 files changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.c b/drivers/scsi/ibmvscsi/ibmvscsi.c
>>> index 04de287..adcd5e8 100644
>>> --- a/drivers/scsi/ibmvscsi/ibmvscsi.c
>>> +++ b/drivers/scsi/ibmvscsi/ibmvscsi.c
>>> @@ -84,6 +84,7 @@
>>>   */
>>>  static int max_id = 64;
>>>  static int max_channel = 3;
>>> +static int max_lun = 8;
>>>  static int init_timeout = 300;
>>>  static int login_timeout = 60;
>>>  static int info_timeout = 30;
>>> @@ -117,6 +118,9 @@ module_param_named(fast_fail, fast_fail, int, S_IRUGO | S_IWUSR);
>>>  MODULE_PARM_DESC(fast_fail, "Enable fast fail. [Default=1]");
>>>  module_param_named(client_reserve, client_reserve, int, S_IRUGO );
>>>  MODULE_PARM_DESC(client_reserve, "Attempt client managed reserve/release");
>>> +module_param(max_lun, int, S_IRUGO);
>>> +MODULE_PARM_DESC(max_lun, "Maximum allowed LUN "
>>> +                          "[Default=8,Max="__stringify(IBMVSCSI_MAX_LUN)"]");
>>>  
>>>  static void ibmvscsi_handle_crq(struct viosrp_crq *crq,
>>>  				struct ibmvscsi_host_data *hostdata);
>>> @@ -2289,7 +2293,7 @@ static int ibmvscsi_probe(struct vio_dev *vdev, const struct vio_device_id *id)
>>>  		goto init_pool_failed;
>>>  	}
>>>  
>>> -	host->max_lun = 8;
>>> +	host->max_lun = max_lun;
>>>  	host->max_id = max_id;
>>>  	host->max_channel = max_channel;
>>>  	host->max_cmd_len = 16;
>>> @@ -2414,6 +2418,9 @@ int __init ibmvscsi_module_init(void)
>>>  {
>>>  	int ret;
>>>  
>>> +	if (max_lun > IBMVSCSI_MAX_LUN)
>>> +		return -EINVAL;
>>> +
>>>  	/* Ensure we have two requests to do error recovery */
>>>  	driver_template.can_queue = max_requests;
>>>  	max_events = max_requests + 2;
>>> diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.h b/drivers/scsi/ibmvscsi/ibmvscsi.h
>>> index 7d64867..1067367 100644
>>> --- a/drivers/scsi/ibmvscsi/ibmvscsi.h
>>> +++ b/drivers/scsi/ibmvscsi/ibmvscsi.h
>>> @@ -48,6 +48,7 @@ struct Scsi_Host;
>>>  #define IBMVSCSI_CMDS_PER_LUN_DEFAULT 16
>>>  #define IBMVSCSI_MAX_SECTORS_DEFAULT 256 /* 32 * 8 = default max I/O 32 pages */
>>>  #define IBMVSCSI_MAX_CMDS_PER_LUN 64
>>> +#define IBMVSCSI_MAX_LUN 32
>>>  
>>>  /* ------------------------------------------------------------
>>>   * Data Structures
>>>
>> Please set max_lun to 31, and remove everything else.
>> As discussed, max_lun is the max number of LUNs supported by the
>> hardware/HBA. There is no point in restricting it further.
> 
> You mean no module parameter and a simple "host->max_lun = 31" ?
> 
Yes.

> I'm wondering if it should be "host->max_lun = 32". What about this ?
> 
'max_lun' is used as the stopping condition while scanning LUNs
sequentially in drivers/scsi/scsi_scan.c:

	for (lun = 1; lun < max_dev_lun; ++lun)
		if ((scsi_probe_and_add_lun(starget, lun, NULL, NULL, rescan,
					    NULL) != SCSI_SCAN_LUN_PRESENT) &&

so indeed it needs to be set to '32'.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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