linux-kernel - Re: [PATCH] ibmvscsis: Initial commit of IBM VSCSI Tgt Driver

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Date:	Fri, 10 Jun 2016 12:03:51 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Bryant G Ly <bryantly@...ux.vnet.ibm.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	<martin.petersen@...cle.com>, <tyreld@...ux.vnet.ibm.com>,
	<akpm@...ux-foundation.org>, <kvalo@...eaurora.org>,
	<davem@...emloft.net>, <gregkh@...uxfoundation.org>,
	<mchehab@....samsung.com>, <jslaby@...e.com>, <joe@...ches.com>,
	<bp@...e.de>, <linux-kernel@...r.kernel.org>,
	<linux-scsi@...r.kernel.org>, <target-devel@...r.kernel.org>,
	bgly <bgly@...ibm.com>
Subject: Re: [PATCH] ibmvscsis: Initial commit of IBM VSCSI Tgt Driver

On 05/24/2016 01:00 PM, Bryant G Ly wrote:
> Quoting Bart Van Assche <bart.vanassche@...disk.com>:
>> On 05/24/2016 06:52 AM, Bryant G. Ly wrote:
>>> +static uint64_t ibmvscsis_unpack_lun(const uint8_t *lun, int len)
>>> +{
>>> +    uint64_t res = NO_SUCH_LUN;
>>> +    int addressing_method;
>>> +
>>> +    if (unlikely(len < 2)) {
>>> +        pr_err("Illegal LUN length %d, expected 2 bytes or more\n",
>>> +            len);
>>> +        goto out;
>>> +    }
>>> +
>>> +    switch (len) {
>>> +    case 8:
>>> +        if ((*((__be64 *)lun) & cpu_to_be64(0x0000FFFFFFFFFFFFLL))
>>> != 0)
>>> +            goto out_err;
>>> +        break;
>>> +    case 4:
>>> +        if (*((__be16 *)&lun[2]) != 0)
>>> +            goto out_err;
>>> +        break;
>>> +    case 6:
>>> +        if (*((__be32 *)&lun[2]) != 0)
>>> +            goto out_err;
>>> +        break;
>>> +    case 2:
>>> +        break;
>>> +    default:
>>> +        goto out_err;
>>> +    }
>>> +
>>> +    addressing_method = (*lun) >> 6; /* highest two bits of byte 0 */
>>> +    switch (addressing_method) {
>>> +    case SCSI_LUN_ADDR_METHOD_PERIPHERAL:
>>> +    case SCSI_LUN_ADDR_METHOD_FLAT:
>>> +    case SCSI_LUN_ADDR_METHOD_LUN:
>>> +        res = *(lun + 1) | (((*lun) & 0x3f) << 8);
>>> +        break;
>>> +
>>> +    case SCSI_LUN_ADDR_METHOD_EXTENDED_LUN:
>>> +    default:
>>> +        pr_err("Unimplemented LUN addressing method %u\n",
>>> +            addressing_method);
>>> +        break;
>>> +    }
>>> +
>>> +out:
>>> +    return res;
>>> +out_err:
>>> +    pr_err("Support for multi-level LUNs has not yet been
>>> implemented\n");
>>> +    goto out;
>>> +}
>>
>> In the above function there is nothing that is specific to the VIO
>> mechanism. Please consider to merge this function with
>> scsilun_to_int(), e.g. by introducing a new function that accepts a
>> SCSI LUN and the addressing method as arguments and by making
>> scsilun_to_int() call that function with
>> SCSI_LUN_ADDR_METHOD_PERIPHERAL as one of its arguments.
>>
>
> We are going to keep this here atm, until we can make sure canonical can
> pick up
> these changes, since we have a deliverable for a 3rd party vendor who is
> going to
> fully utilize this driver. Once they can pick it up in 4.4 kernel I will
> make the
> change you recommended / move the scsi_lun_addr_method addressed below.
> I will also
> address the changes that ib_srpt needs to utilize this new function too.

A much better approach would be to move this function into the SCSI core 
and to add a copy of that function to the backported driver that will be 
provided to Canonical.

Thanks,

Bart.