scst_lib: Allow REPORT LUNS to operate on an unsupported LUN

[bmeagherix]

Initiators will attempt to send LUN 0 INQUIRY and REPORT LUNS commands when connecting to a target. If a SCST target is configured with LUNs e.g. 100, 101 (i.e. no LUN 0) then disks would NOT surface when iscsiadm is used to login on Linux. This PR is to modify SCST behavior to rectify this.

• Add scst_set_lun_not_supported_report_luns to handle the case when REPORT LUNs is sent to an unsupported LUN.
• Also, in scst_set_lun_not_supported_inquiry report a valid vendor identification string to promote better initiator behavior.

Tested with SCST running on:

• Linux 6.1.20
• Linux 6.6.16

Tested with clients:

• Linux kernel 6.6.16 / iscsiadm version 2.1.8
• Linux kernel 5.10.191 / iscsiadm version 2.1.3
• Windows 11

---

open-iscsi/open-iscsi#175 is not wrt SCST, but offers some interesting insight nonetheless. Specifically:

• Linux kernel was having difficulty with empty vendor/model, hence the proposed change to scst_set_lun_not_supported_inquiry.
• The extract from SAM 5 4.7.4, hence scst_set_lun_not_supported_report_luns

All SCSI target devices shall support LUN 0 (i.e., 00000000 00000000h) or the REPORT LUNS well known logical unit. For SCSI target devices that support complex LUN structures (see 4.7.6) the LUN 0 or the REPORT LUNS well known logical unit shall be the logical unit that an application client addresses to determine information about the SCSI target device and the logical units contained within the SCSI target device.

The code in scst_set_lun_not_supported_report_luns was inspired by scst_set_lun_not_supported_inquiry and scst_report_luns_local.

[lnocturno]

Hi Brian,

Thank you for the patch!

Thanks,
Gleb