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

[Nicholas A. Bellinger]

From: Nicholas Bellinger <nab at linux-iscsi.org>

Greetings Tomo and Mike,

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(-)

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