[stgt] [PATCH 3/3] [tgt]: Add BSG v4 backstore support to usr/bs_sg.c

[Nicholas A. Bellinger]

On Mon, 2010-06-07 at 13:35 +0300, Boaz Harrosh wrote:
> 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 at linux-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 at linux-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?

Hmmm, suppose I need to read up a bit on how to generate osd_tgtd
traffic..

>  what does the TCM_Loop
> do exactly. Please forgive my laziness, I never took the time to find out.
> 

TCM_Loop is a TCM fabric module that appears under /sys/kernel/config/target/loopback/
that emulates SAS, FC and iSCSI WWPN Ports and their assocated I_T Nexus
for SPC-4 PR and ALUA operations.  TCM_Loop registers as a Linux/SCSI
LLD (a la scsi_debug) that presents TCM backstores (IBLOCK, FILEIO,
RAMDISK) as a local struct scsi_device with a complete set of WWN port
naming identifiers (sg_inq -i) and TransportIDs (for PR).

With TCM v4 code in lio-core-2.6.git/lio-4.0, TCM_Loop has been
converted along with the rest of the v4.x fabric modules to use a
generic set of struct config_group logic from
drivers/target/target_core_fabric_configfs.c.  There is a bit of
information on the wiki at:

http://linux-iscsi.org/index.php/TCM_loop

but as you will notice the screenshots are still referencing the
original tests from last year with VMware Workstation.  Things have
changed quite a bit since then as TCM_Loop has gone from using internal
SAS WWPN+Nexus emulation to providing multi-protocol support based on
configfs provided WWPNs using the new generic naming handers from
drivers/target/target_core_fabric_lib.c

Best,

--nab

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