Linux Configuration HP VA 7100/7400

Linux Configuration
HP VA 7100/7400
Rev 2002-01-23 Page 7
Recommendation: This patch is required if managing the VA 7100/7400 through a Linux host. If
other device management options are pursued, this patch is not required.
Files Affected: ../linux/drivers/scsi/qlogicfc.c
2.1.2 16-Byte SCSI CDBs
Problem synopsis: The Linux 2.2 kernel SCSI subsystem supports command descriptor blocks
(CDBs) up to 12 bytes in length. The constant, MAX_COMMAND_SIZE, defines this length but is
not used consistently throughout the SCSI source code. In many places a CDB size of 12 bytes is
hard-coded. Several management features specific to the VA 7100/7400 require 16-byte CDBs.
Patch description: This patch to the SCSI mid-layer removes all hard-coded size restrictions on
CDB data structures. All such data structures now reference the MAX_COMMAND_SIZE constant,
which has also been increased to 16 bytes.
Caveats: This patch applies to the entire SCSI subsystem, not just fibre-channel devices. All
processing of SCSI command data structures will now involve manipulating a 16-byte field instead of
the typical 12 bytes. This is a modest amount of overhead to support the few commands which require
16-byte CDBs.