linux-kernel - Re: [PATCH 3/3] [tgt]: Add BSG v4 backstore support to usr/bs

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Date:	Mon, 07 Jun 2010 13:35:21 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
CC:	stgt-devel <stgt@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	James Bottomley <James.Bottomley@...e.de>,
	Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH 3/3] [tgt]: Add BSG v4 backstore support to usr/bs_sg.c

On 06/07/2010 12:37 PM, Nicholas A. Bellinger wrote:
> On Mon, 2010-06-07 at 12:27 +0300, Boaz Harrosh wrote:
>> On 06/07/2010 12:02 PM, Nicholas A. Bellinger wrote:
>>> On Mon, 2010-06-07 at 11:40 +0300, Boaz Harrosh wrote:
>>>> On 06/07/2010 06:50 AM, Nicholas A. Bellinger wrote:
>>>>> From: Nicholas Bellinger <nab@...ux-iscsi.org>
>>>>>
>>>>> This patch adds initial support for the block layer implementation of the sg v4 interface
>>>>> (BSG) -> STGT with a new struct backingstore_template bsg_bst sharing code with the
>>>>> original sg_bst.  It adds for new function bs_bsg_cmd_submit() for incoming write I/O
>>>>> and bs_bsg_cmd_complete() for polling read I/O using include/linux/bsg.h:struct sg_io_v4.
>>>>>
>>>>> This patch also splits up bs_sg_open() to support both BSG and SG looking for the
>>>>> path "/dev/bsg" in bs_sg_open(), and getting max_queue using SG_GET_COMMAND_Q and
>>>>> calling SG_SET_RESERVED_SIZE (following the original bs_sg code in init_sg_device)
>>>>>
>>>>> Also chk_bsg_device() currently using a hardcoded 254 major as def for BSG does not
>>>>> appear in include/linux/major.h just yet..
>>>>>
>>>>> So far this has been tested with STGT/iSCSI <-> BSG <-> TCM_Loop SPC-4 iSCSI Target
>>>>> Port emulation and is able to mkfs, fsck and mount a filesystem from a TCM/IBLOCK
>>>>> Linux LVM kernel level backstore
>>>>>
>>>>> Signed-off-by: Nicholas A. Bellinger <nab@...ux-iscsi.org>
>>>>> ---
>>>>>  usr/bs_sg.c     |  178 +++++++++++++++++++++++++++++++++++++++++++++++++++---
>>>>>  usr/scsi_cmnd.h |    7 ++
>>>>>  2 files changed, 175 insertions(+), 10 deletions(-)
>>>>>
>>>>> diff --git a/usr/bs_sg.c b/usr/bs_sg.c
>>>>> index 23676ef..d071714 100644
>>>>> --- a/usr/bs_sg.c
>>>>> +++ b/usr/bs_sg.c
>>>
>>> <SNIP>
>>>
>>>>> +
>>>>> +static int bs_bsg_cmd_submit(struct scsi_cmd *cmd)
>>>>> +{
>>>>> +	struct scsi_lu *dev = cmd->dev;
>>>>> +	int fd = dev->fd;
>>>>> +	struct sg_io_v4 *io_hdr = &cmd->cmd_bsg_hdr;
>>>>> +	int err = 0;
>>>>> +	/*
>>>>> +	 * Following linux/include/linux/bsg.h
>>>>> +	 */
>>>>> +	/* [i] 'Q' to differentiate from v3 */
>>>>> +	io_hdr->guard = 'Q';
>>>>> +	io_hdr->protocol = BSG_PROTOCOL_SCSI;
>>>>> +	io_hdr->subprotocol = BSG_SUB_PROTOCOL_SCSI_CMD;
>>>>> +	io_hdr->request_len = cmd->scb_len;
>>>>> +	io_hdr->request = (unsigned long )cmd->scb;
>>>>> +
>>>>> +	if (scsi_get_data_dir(cmd) == DATA_WRITE) {
>>>>
>>>> Why the if? both sides are fully bidi just remove the ifs
>>>> and: OUT <= OUT, IN <= IN
>>>>
>>>
>>> Whoops, thanks for pointing this one out (again).  Tested with
>>> unidirection commands and included into my local tgt.git/pass that I
>>> will send along to Tomo-san..
>>>
>>> Btw, I still need to sort out BIDI support for TCM_Loop at some point in
>>> the not too distant future.  What would be a good way to generate BIDI
>>> traffic into STGT or a local SCSI LLD..?
>>
>> scsi_debug has some emulation for XOR commands, does that help?
>>
> 
> Great, thanks for the pointer on the LLD side.  Is there any userspace
> code around that will generate XDWRITEREAD_* CDBs for bulk I/O or do I
> need to code this part myself..?
> 
> Best,
> 
> --nab
> 

You could use iscsi as LLD and generate OSD heavy traffic. (With a real osd_tgtd
on the end side). But that will need more work, right? what does the TCM_Loop
do exactly. Please forgive my laziness, I never took the time to find out.

Boaz
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