Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031642AbbKDXGz (ORCPT ); Wed, 4 Nov 2015 18:06:55 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:33107 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031459AbbKDXGw (ORCPT ); Wed, 4 Nov 2015 18:06:52 -0500 X-IBM-Helo: d01dlp03.pok.ibm.com X-IBM-MailFrom: brking@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-scsi@vger.kernel.org Subject: Re: [PATCH v2 3/3] ibmvscsi: Allow to configure maximum LUN To: Hannes Reinecke , Laurent Vivier , martin.petersen@oracle.com References: <1446632451-22365-1-git-send-email-lvivier@redhat.com> <1446632451-22365-4-git-send-email-lvivier@redhat.com> <5639E904.1070100@suse.de> <5639F020.4010308@redhat.com> <563A01CC.20809@suse.de> Cc: tyreld@linux.vnet.ibm.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org From: Brian King Message-ID: <563A8F83.7010601@linux.vnet.ibm.com> Date: Wed, 4 Nov 2015 17:06:43 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <563A01CC.20809@suse.de> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15110423-0033-0000-0000-000006B57AC9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3735 Lines: 99 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 >>>> --- >>>> 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. -Brian -- Brian King Power Linux I/O IBM Linux Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/