[stgt] [PATCH 0/2] [tgt]: Add proper SG_IO struct cmd CDB passthrough

[Nicholas A. Bellinger]

On Tue, 2010-05-18 at 13:39 +0900, FUJITA Tomonori wrote:
> On Mon, 17 May 2010 22:12:54 -0700
> "Nicholas A. Bellinger" <nab at linux-iscsi.org> wrote:
> 
> > These are two patches to allow the STGT SG_IO backstore to function using a
> > new struct scsi_cmd->sg_iovec member with sg_io_hdr->iovec_count=1, and to update
> > usr/scsi.c:scsi_cmd_perform() to allow for a hand off incoming descriptors into the
> > struct device_type_template->cmd_passthrough() function pointer.
> > 
> > I initially updated usr/sbc.c to set sbc_rw() as it's CDB passthrough function for
> > TYPE_DISK, but the logic should apply to any device types *_rw() functions.  Please let
> > me know if this makes sense, and I will look at updating the other stgt device types.
> > 
> > So far with this patch, I am able to successfully mkfs new iSCSI TYPE_DISK LUNS with
> > Open-iSCSI to the userspace STGT iSCSI fabric module + SG_IO into kernel level TCM_Loop
> > virtual iSCSI target ports on a x86 HVM, and bulk 512KB DATA_SG_IO payloads between STGT
> > and TCM_Loop are now functioning as expected.
> > 
> > There is one unresolved issue that I ran into while running initially with TCM_Loop
> > and struct scsi_device->max_sectors=256.  SG_IO writes larger than the
> > struct scsi_device->max_sectors are being returned with -EINVAL, but it appears that
> > the CHECK_CONDITION is not actually being propigated back into STGT/iSCSI.
> > 
> > After increasing the TCM_Loop ports to struct scsi_device->max_sectors=1024 following
> > the Open-iSCSI Initiator default, the 512KB paylods begin work as expected.  I will need
> > to have a look at the case for CDB length > max_sectors, which means that bs_sg.c getting
> > the correct scsi_status and sense data out of the kernel might still need more work.
> > 
> > In the mean time, please have a look at applying these patches.
> > 
> > Best,
> > 
> > Signed-off-by: Nicholas A. Bellinger <nab at linux-iscsi.org>
> > 
> > Nicholas Bellinger (2):
> >   [tgt]: Add proper CDB passthrough for SG_IO backstores
> >   [tgt]: Add support for SG_IO CDB passthrough in scsi_cmd_perform()
> > 
> >  usr/bs_sg.c     |   31 ++++++++++++++++++++++++-------
> >  usr/sbc.c       |    1 +
> >  usr/scsi.c      |   11 +++++++++++
> >  usr/scsi_cmnd.h |    4 ++++
> >  usr/tgtd.h      |    2 ++
> >  5 files changed, 42 insertions(+), 7 deletions(-)
> 
> Thanks! Surely, the first patch looks fine.
> 

Great!   Please let me know if I should also generate patches for
conversion of remaining STGT struct device_type_templates for proper
SG_IO passthrough support.

> I thought that you want to send all SCSI commands to your in-kernel
> target code via SG_IO. That's, you want the proper 'pass-through' code
> since tgt's pass-through code is broken.
> 
> However, looks like non I/O commands are still performed in user-space
> tgt code and only I/O commands goes to kernel via SG_IO. Hmm, that's
> what you want to do?

Hmmm, not sure what you mean here..

AFAICT using the newly provided struct
device_type_template->cmd_passthrough() instead CDB emulation specific
callers in usr/scsi.c:scsi_cmd_perform() with device type template
   
	cmd->dev->dev_type_template.ops[op].cmd_perform(()

will always capture incoming struct scsi_cmnd for SG_IO passthrough
before the device type CDB userspace STGT emulation execution and hand
off into .cmd_perform()..?

This is why the patches to use sbc_rw() as device type passthrough works
for TYPE_DISK into SG_IO backstores with [READ,WRITE]_[6,10,12,16])
CDBs, yes?

Best,

--nab


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