From: Brian King <brking@linux.vnet.ibm.com>
To: Laurent Vivier <lvivier@redhat.com>,
Hannes Reinecke <hare@suse.de>,
martin.petersen@oracle.com
Cc: tyreld@linux.vnet.ibm.com, linux-scsi@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] ibmvscsi: Allow to configure maximum LUN
Date: Thu, 5 Nov 2015 14:00:43 -0600 [thread overview]
Message-ID: <563BB56B.5090709@linux.vnet.ibm.com> (raw)
In-Reply-To: <563B12D1.1050000@redhat.com>
On 11/05/2015 02:26 AM, Laurent Vivier wrote:
>
>
> On 05/11/2015 00:06, Brian King wrote:
>> On 11/04/2015 07:02 AM, Hannes Reinecke wrote:
>>> On 11/04/2015 12:46 PM, Laurent Vivier wrote:
>>>>
>>>>
>>>> On 04/11/2015 12:16, Hannes Reinecke wrote:
>>>>> On 11/04/2015 11:20 AM, Laurent Vivier wrote:
>>>>>> QEMU allows until 32 LUNs.
>>>>>>
>>>>>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>>>>>> ---
>>>>>> drivers/scsi/ibmvscsi/ibmvscsi.c | 5 ++++-
>>>>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/scsi/ibmvscsi/ibmvscsi.c b/drivers/scsi/ibmvscsi/ibmvscsi.c
>>>>>> index 04de287..4480d3e 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 +118,8 @@ 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 LUN value [Default=8]");
>>>>>>
>>>>>> static void ibmvscsi_handle_crq(struct viosrp_crq *crq,
>>>>>> struct ibmvscsi_host_data *hostdata);
>>>>>> @@ -2289,7 +2292,7 @@ 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;
>>>>>>
>>>>> Please, don't do this.
>>>>>
>>>>> 'max_lun' should only be set if the HBA / transport has some hard
>>>>> limitations on the number of bytes it can use.
>>>>> Otherwise the scanning algorithm in scsi_scan.c should do the
>>>>> correct thing, independent on the 'max_lun' setting.
>>>>
>>>> So you are saying we can remove the line ?
>>>>
>>> Ho-hum. In principle you could, as ibmvscsi is using SRP internally,
>>> which does support 64 bit LUNs.
>>>
>>> However, due to some weird design decisions there is
>>> the function 'lun_from_dev()', which mangles the incoming LUN number
>>> into something ... else.
>>> Which leaves only 4 bits free for the actual LUN number, requiring
>>> you to use max_lun = 16.
>>>
>>> Personally I would just do away with that function and use the
>>> incoming LUN numbers as is.
>>
>> I pulled out my copy of SAM, what lun_from_dev is doing is translating
>> the incoming bus / id / LUN to a LUN in the logical unit addressing format,
>> as defined in 4.6.9 of SAM-4.
>>
>> --------------------------------------
>> |Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
>> --------------------------------------
>> | n | (10b) | Target |
>> --------------------------------------
>> | n+1| Bus | LUN |
>> --------------------------------------
>>
>> So this means, in the current implementation, we have 6 bits for target (max=63),
>> 3 bits for bus (max=7), and 5 bits for LUN (max=31).
>>
>> It might not be a bad idea to enforce these limits on the module parameters. Otherwise
>> we'll have a mess when we run through lun_from_dev...
>>
>> As far as eliminating lun_from_dev and just passing the LUN through, I don't think we
>> can do that. The LUN list returned by Report LUNs to a VSCSI disk assumes we are
>> doing the translation above.
>
> So what I understand is this patch is OK but I have to check the given
> value is less than 32 (the same max value as for QEMU) ?
As far as I'm concerned, yes.
Thanks,
Brian
--
Brian King
Power Linux I/O
IBM Linux Technology Center
next prev parent reply other threads:[~2015-11-05 20:00 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-04 10:20 [PATCH v2 0/3] ibmvscsi parameter cleanup Laurent Vivier
2015-11-04 10:20 ` [PATCH v2 1/3] ibmvscsi: make parameters max_id and max_channel read-only Laurent Vivier
2015-11-04 10:20 ` [PATCH v2 2/3] ibmvscsi: display default value for max_id, max_lun and max_channel Laurent Vivier
2015-11-04 10:20 ` [PATCH v2 3/3] ibmvscsi: Allow to configure maximum LUN Laurent Vivier
2015-11-04 10:24 ` Laurent Vivier
2015-11-04 11:16 ` Hannes Reinecke
2015-11-04 11:46 ` Laurent Vivier
2015-11-04 13:02 ` Hannes Reinecke
2015-11-04 23:06 ` Brian King
2015-11-05 8:26 ` Laurent Vivier
2015-11-05 20:00 ` Brian King [this message]
2015-11-05 8:51 ` Hannes Reinecke
2015-11-05 19:01 ` Brian King
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