gotgt/docs/SCSI_COMMANDS.md

SCSI Commands Support

This document lists all SCSI commands supported by gotgt iSCSI target implementation.

Overview

gotgt implements SCSI Primary Commands (SPC-3/4) and SCSI Block Commands (SBC-2/3) to provide a complete iSCSI target solution for block storage devices.

Supported SCSI Commands

SPC Commands (Primary Commands)

Opcode	Command Name	Description	Status
0x00	TEST UNIT READY	Check if device is ready	✅ Supported
0x03	REQUEST SENSE	Request sense data	✅ Supported
0x12	INQUIRY	Get device information	✅ Supported
0x1A	MODE SENSE (6)	Get device parameters	✅ Supported
0x5A	MODE SENSE (10)	Get device parameters	✅ Supported
0x15	MODE SELECT (6)	Set device parameters	✅ Supported
0x55	MODE SELECT (10)	Set device parameters	✅ Supported
0x1B	START STOP UNIT	Control device power state	✅ Supported
0x1E	PREVENT ALLOW MEDIUM REMOVAL	Control media removal	✅ Supported
0xA0	REPORT LUNS	Report LUN inventory	✅ Supported
0x1D	SEND DIAGNOSTIC	Run diagnostics	✅ Supported
0x5E	PERSISTENT RESERVE IN	Read reservation info	✅ Supported
0x5F	PERSISTENT RESERVE OUT	Modify reservations	✅ Supported
0xA3	MAINTENANCE IN	Maintenance commands	✅ Supported (Report Supported Operation Codes)

SBC Commands (Block Commands)

Opcode	Command Name	Description	Status
0x08	READ (6)	Read data (21-bit LBA)	✅ Supported
0x28	READ (10)	Read data (32-bit LBA)	✅ Supported
0xA8	READ (12)	Read data (32-bit LBA)	✅ Supported
0x88	READ (16)	Read data (64-bit LBA)	✅ Supported
0x0A	WRITE (6)	Write data (21-bit LBA)	✅ Supported
0x2A	WRITE (10)	Write data (32-bit LBA)	✅ Supported
0xAA	WRITE (12)	Write data (32-bit LBA)	✅ Supported
0x8A	WRITE (16)	Write data (64-bit LBA)	✅ Supported
0x2E	WRITE AND VERIFY (10)	Write and verify	✅ Supported
0xAE	WRITE AND VERIFY (12)	Write and verify	✅ Supported
0x8E	WRITE AND VERIFY (16)	Write and verify	✅ Supported
0x41	WRITE SAME (10)	Write same pattern	✅ Supported
0x93	WRITE SAME (16)	Write same pattern	✅ Supported
0x8B	ORWRITE (16)	OR write operation	✅ Supported
0x89	COMPARE AND WRITE	Atomic compare and write	✅ Supported
0x25	READ CAPACITY (10)	Get device capacity	✅ Supported
0x9E	SERVICE ACTION IN (16)	Read capacity (16)	✅ Supported
0x2F	VERIFY (10)	Verify data integrity	✅ Supported
0xAF	VERIFY (12)	Verify data integrity	✅ Supported
0x8F	VERIFY (16)	Verify data integrity	✅ Supported
0x34	PRE-FETCH (10)	Cache data	✅ Supported
0x90	PRE-FETCH (16)	Cache data	✅ Supported
0x35	SYNCHRONIZE CACHE (10)	Flush cache	✅ Supported
0x91	SYNCHRONIZE CACHE (16)	Flush cache	✅ Supported
0x42	UNMAP	Deallocate blocks	✅ Supported
0x04	FORMAT UNIT	Format media	✅ Supported
0x16	RESERVE (6)	Reserve device	✅ Supported
0x17	RELEASE (6)	Release device	✅ Supported

Persistent Reservation Service Actions

PR IN Service Actions

Service Action	Name	Description	Status
0x00	READ KEYS	Read reservation keys	✅ Supported
0x01	READ RESERVATION	Read current reservation	✅ Supported
0x02	REPORT CAPABILITIES	Report PR capabilities	✅ Supported

PR OUT Service Actions

Service Action	Name	Description	Status
0x00	REGISTER	Register reservation key	✅ Supported
0x01	RESERVE	Reserve device	✅ Supported
0x02	RELEASE	Release reservation	✅ Supported
0x03	CLEAR	Clear all reservations	✅ Supported
0x04	PREEMPT	Preempt reservation	✅ Supported
0x06	REGISTER AND IGNORE EXISTING KEY	Register new key	✅ Supported
0x07	REGISTER AND MOVE	Register and move	✅ Supported

Supported VPD Pages

The INQUIRY command supports the following Vital Product Data (VPD) pages:

Page Code	Name	Description	Status
0x00	Supported VPD Pages	List of supported VPD pages	✅ Supported
0x80	Unit Serial Number	Device serial number	✅ Supported
0x83	Device Identification	Device identifiers	✅ Supported
0xB0	Block Limits	Block device limits	✅ Supported
0xB2	Logical Block Provisioning	Thin provisioning info	✅ Supported

Supported Mode Pages

The MODE SENSE command supports the following mode pages:

Page Code	Name	Description	Status
0x02	Disconnect-Reconnect	Disconnect/reconnect parameters	✅ Supported
0x08	Caching	Cache control parameters	✅ Supported
0x0A	Control	Control mode parameters	✅ Supported
0x0A/0x01	Control Extension	Extended control parameters	✅ Supported
0x1C	Informational Exceptions	SMART control parameters	✅ Supported

iSCSI Protocol Features

Feature	Description	Status
Login Authentication	CHAP authentication	✅ Supported
Multiple Connections	Multiple TCP connections per session	✅ Supported
Header Digest	CRC32C header integrity	✅ Supported
Data Digest	CRC32C data integrity	✅ Supported
Immediate Data	Immediate data delivery	✅ Supported
Unsolicited Data	Unsolicited data-out PDUs	✅ Supported
Error Recovery Level	Error recovery mechanisms	Level 0 Supported

Tested with libiscsi

All commands have been tested with the libiscsi test suite. The following test categories are fully supported:

• ✅ Inquiry commands (including EVPD handling)
• ✅ Read operations (6/10/12/16 byte CDBs)
• ✅ Write operations (6/10/12/16 byte CDBs)
• ✅ Write and Verify operations
• ✅ Verify operations
• ✅ Capacity reporting
• ✅ Mode Sense/Select operations
• ✅ Persistent Reservation operations
• ✅ Unmap/Trim operations
• ✅ Synchronize Cache operations
• ✅ iSCSI protocol compliance

Test Results

Total Tests: 38
Passed: 38
Failed: 0
Pass Rate: 100%

Tested with libiscsi test suite covering all major SCSI command categories.

Recent Fixes

Bug Fix: SCSICDBBufXLength Function (2025-03-10)

Fixed incorrect Allocation Length calculation for 6-byte CDB commands:

1. INQUIRY (0x12) and REQUEST_SENSE (0x03): Use bytes 3-4 for Allocation Length
2. Other Group 0 commands (READ_6, WRITE_6, etc.): Return ok=false since these commands don't have Allocation Length field in their CDB. This prevents incorrect truncation of sense data buffer.

Bug Fix: CDB Group ID Comparison (2025-03-10)

Fixed incorrect comparison between CDB length constants and group IDs:

• Original: Used CDB length constants (6, 10, 12, 16) which were incorrect
• Fixed: Use actual group IDs (0-7) for switch statement

Bug Fix: PERSISTENT_RESERVE_IN/OUT (0x5E/0x5F) (2025-03-10)

Fixed Allocation Length position for these commands:

• Use bytes 6-7 instead of bytes 7-8
• Added manual BigEndian conversion for correct byte order

Notes

Block Device Characteristics VPD Page (0xB1)

This VPD page is currently not supported. The INQUIRY command will return a CHECK CONDITION status with ILLEGAL_REQUEST sense key when this page is requested. This is expected behavior and does not affect normal operations.

Persistent Reservations

• All standard reservation types are supported: Write Exclusive, Exclusive Access, and their variants with registrants only.
• Reservation scopes: LU (Logical Unit) scope is supported.
• Persistent reservation operations require proper key registration before use.

Thin Provisioning

• UNMAP command is fully supported for thin-provisioned LUNs.
• Logical Block Provisioning VPD page (0xB2) reports thin provisioning capabilities.

Version Information

• SPC Version: SPC-3 (with some SPC-4 features)
• SBC Version: SBC-2 (with some SBC-3 features)
• iSCSI Protocol: RFC 3720 compliant

References

• SCSI Primary Commands - 4 (SPC-4)
• SCSI Block Commands - 3 (SBC-3)
• iSCSI Protocol (RFC 3720)
• libiscsi Test Suite