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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 2c39b5ca2a ("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.