HP SureStore 7400 Linux Configuration HP VA 7100/7400 - Page 7

Recommendation, Files Affected, Byte SCSI CDBs, Problem synopsis, Patch description, Caveats

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Linux Configuration HP VA 7100/7400 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. Rev 2002-01-23 Page 7

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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.