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

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Message-Id: <1275901324.26888.56.camel@haakon2.linux-iscsi.org>
Date:	Mon, 07 Jun 2010 02:02:04 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Boaz Harrosh <bharrosh@...asas.com>
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 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..?

Best,

--nab

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