mirror of
https://github.com/SCST-project/scst.git
synced 2026-05-14 09:11:27 +00:00
46e11e4b32
Background: loading qla2xxx with "ql2xtgt_tape_enable=1" enables
Sequence Level Error Recovery (SLER), which is most commonly used for
tape drives. With SLER enabled, if there is a recoverable I/O error
during a SCSI command, a Sequence Retransmission Request (SRR) will be
used to retry the I/O at a low-level completely within the driver
without propagating the error to the upper levels of the SCSI stack.
SRR support was removed in 2017 by commit 2c39b5ca2a8c ("qla2xxx: Remove
SRR code"). Add it back, new and improved.
The old removed SRR code used sequence numbers to correlate the SRR
CTIOs with SRR immediate notify messages. I don't see how that would
work reliably with MSI-X interrupts and multiple queues. So instead use
the exchange address to find the command associated with the immediate
notify (qlt_srr_to_cmd).
The old removed SRR code had a function qlt_check_srr_debug() to
simulate a SRR, but it didn't work for me. Instead I just used fiber
optic attenuators attached to the FC cable to reduce the strength of the
signal and induce errors. Unfortunately this only worked for inducing
SRRs on Data-Out (write) commands, so that is all I was able to test.
The code to build a new scatterlist for a SRR with nonzero offset has
been improved to reduce memory requirements and has been well-tested.
However it does not support protection information.
When a single cmd gets multiple SRRs, the old removed SRR code would
restore the data buffer from the values in cmd->se_cmd before processing
the new SRR. That might be needed if the offset for the new SRR was
lower than the offset for the previous SRR, but I am not sure if that
can happen. In my testing, when a single cmd gets multiple SRRs, the
SRR offset always increases or stays the same. But in case it can
decrease, I added the function qlt_restore_orig_sg(). If this is not
supposed to happen then qlt_restore_orig_sg() can be removed to simplify
the code.
I ran into some HBA firmware bugs with QLE269x, QLE27xx, and QLE28xx
firmware 9.05.xx - 9.08.xx where a SRR would cause the HBA to misbehave
badly. Since SRRs are rare and therefore difficult to test, I figured
it would be worth checking for the buggy firmware and disabling SLER
with a warning instead of letting others run into the same problem on
the rare occasion that they get a SRR. This turned out to be difficult
because the firmware version isn't known in the normal NVRAM config
routine, so I added a second NVRAM config routine that is called after
the firmware version is known.
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Link: https://patch.msgid.link/654b7181-b79e-40ed-a15b-6d6e441a5d5f@cybernetics.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[ commit c7bd85a7b9c5 upstream ]
Overview
This is the source code repository of the SCST project. SCST is a collection of Linux kernel drivers that implement SCSI target functionality. The SCST project includes:
- The SCST core in the scst/ subdirectory.
- A tool for loading, saving and modifying the SCST configuration in directory scstadmin/.
- Several SCSI target drivers in the directories iscsi-scst/, qla2x00t/, srpt/, scst_local/ and fcst/.
- User space programs in the usr/ subdirectory, e.g. fileio_tgt.
- Various documentation in the doc/ subdirectory.
Instructions for building and installing SCST are available in the INSTALL.md file.
QLogic target driver
Two QLogic target drivers are included in the SCST project.
The default driver is located in qla2x00t-32gbit directory and it supports up to 32 Gb/s FC. It is the newer one.
May anyone wish to switch back to the older driver that only supported up to
16 Gb/s adapters, it is located in qla2x00t directory. To make use of the
older driver build scst with environment variable QLA_32GBIT=no set.
Vladislav Bolkhovitin vst@vlnb.net, http://scst.sourceforge.net
Sourceforge achievements
