Re: Possible Bug? LIO does not support SCSI commands with Immediate Bit Set?

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On 11/25/23 10:28, Lee Duncan wrote:
Hi Martin/list:

I am trying to track down an issue I am seeing when trying to boot using iSCSI root using the fastlinq qedi converged network adapter initiator and an LIO target.

In this configuration, but using a non-LIO (hardware) iSCSI target, everything "just works". But when I switch to using an LIO software target, I get this error when booting:

2023-09-20T14:10:32.835358-0500 worker5 kernel: Illegally set Immediate Bit in iSCSI Initiator Scsi Command PDU. ... > 2023-09-20T14:10:32.835422-0500 worker5 kernel: Got unknown iSCSI
OpCode: 0x52

It looks like the fastlinq adapter is sending a SCSI write (0x12) with the Immediate bit set (0x40).

The code in iscsi_target.c:iscsit_setup_scsi_cmd(): looks like this:

    if (hdr->opcode & ISCSI_OP_IMMEDIATE) {
        pr_err("Illegally set Immediate Bit in iSCSI Initiator"
                " Scsi Command PDU.\n");
        return iscsit_add_reject_cmd(cmd,
                         ISCSI_REASON_BOOKMARK_INVALID, buf);
    }


But I looked at rfc3720, and it looks like SCSI PDUs can have the Immediate Bit set:

10.3.  SCSI Command
   The format of the SCSI Command PDU is:
   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x01      |F|R|W|. .|ATTR | Reserved                      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| Logical Unit Number (LUN)                                     |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
...

Where "I" is the immediate bit.

Frankly, I'm never sure I read the SPEC correctly, so I'm not sure if I'm mistaken here, but it looks like LIO does not allow the Immediate bit (and hence Immediate data), even though the SPEC does allow it. But it also looks like, during negotiation phase, LIO negotiates ImmediateData like any other parameter, allowing "YES".

In our testing, if we set ImmediateData=No in the target, then our problem goes away, i.e. we can now boot from an LIO target. This is because Immediate Data is negotiated off, of course.

Is this a bug, or is this adapter doing something wrong? I would appreciate other viewpoints.

Thank you.


Note: I have sent a set of two patches for this, but evidently my mailer is considered SPAM now? I'm working on getting it figured out.

--
Lee Duncan





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