Technical Reference: Kernel and Subsystems, Volume 2

rmt SCSI Device Driver

Purpose

Supports the sequential access bulk storage medium device driver.

Syntax

#include  <sys/devinfo.h>
#include  <sys/scsi.h>
#include  <sys/tape.h>

Note

The /dev/rmt0 through /dev/rmt255 special files provide access to magnetic tapes. Magnetic tapes are used primarily for backup, file archives, and other offline storage.

Device-Dependent Subroutines

Most tape operations are implemented using the open, read, write, and close subroutines. However, the openx subroutine must be used if the device is to be opened in Diagnostic mode.

open and close Subroutines

The openx subroutine is intended for use by the diagnostic commands and utilities. Appropriate authority is required for execution. Attempting to execute this subroutine without the proper authority causes the subroutine to return a value of -1 and sets the errno global variable to EPERM.

The openx subroutine allows the device driver to enter Diagnostic mode and disables command-retry logic. This action allows for execution of ioctl operations that perform special functions associated with diagnostic processing. Other openx capabilities, such as forced opens and retained reservations, are also available.

The ext parameter passed to the openx subroutine selects the operation to be used for the target device. The ext parameter is defined in the /usr/include/sys/scsi.h file. This parameter can contain any combination of the following flag values logically ORed together:

Flag Value	Description
SC_DIAGNOSTIC	Places the selected device in Diagnostic mode. This mode is singularly entrant. When a device is in Diagnostic mode, SCSI operations are performed during open or close operations and error logging is disabled. In Diagnostic mode, only the close and ioctl operations are accepted. All other device-supported subroutines return a value of -1, with the errno global variable set to a value of EACCES. A device can be opened in Diagnostic mode only if the target device is not currently opened. If an attempt is made to open a device in Diagnostic mode and the target device is already open, a value of -1 is returned and the errno global variable is set to EACCES.
SC_FORCED_OPEN	Forces a bus device reset (BDR) regardless of whether another initiator has the device reserved. The SCSI bus device reset is sent to the device before the open sequence begins. Otherwise, the open operation executes normally.
SC_RETAIN_RESERVATION	Retains the reservation of the device after a close operation by not issuing the release. This flag prevents other initiators from using the device unless they break the host machine's reservation.

"SCSI Options to the openx Subroutine" in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts gives more specific information on the open operations.

ioctl Subroutine

The STIOCMD ioctl operation provides the means for sending SCSI commands directly to a tape device. This allows an application to issue specific SCSI commands that are not directly supported by the tape device driver.

To use the STIOCMD operation, the device must be opened in Diagnostic mode. If this command is attempted while the device is not in Diagnostic mode, a value of -1 is returned and the errno global variable is set to a value of EACCES. The STIOCMD operation passes the address of a sc_iocmd structure. This structure is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for information on issuing the parameters.

Error Conditions

In addition to those errors listed, ioctl, open, read, and write subroutines against this device are unsuccessful in the following circumstances:

Error	Description
EACCES	Indicates that a diagnostic command was issued to a device not in Diagnostic mode.
EAGAIN	Indicates that an attempt was made to open a device that was already open.
EBUSY	Indicates that the target device is reserved by another initiator.
EINVAL	Indicates that a value of O_APPEND is supplied as the mode in which to open.
EINVAL	Indicates that the nbyte parameter supplied by a read or write operation is not a multiple of the block size.
EINVAL	Indicates that a parameter to an ioctl operation is not valid.
EINVAL	Indicates that the requested ioctl operation is not supported on the current device.
EIO	Indicates that the tape drive has been reset or that the tape has been changed. This error is returned on open if the previous operation to tape left the tape positioned beyond beginning of tape upon closing.
EIO	Indicates that the device could not space forward or reverse the number of records specified by the `st_count` field before encountering an EOM (end of media) or a file mark.
EMEDIA	Indicates that the tape device has encountered an unrecoverable media error.
EMFILE	Indicates that an open operation was attempted for a SCSI adapter that already has the maximum permissible number of open devices.
ENOTREADY	Indicates that there is no tape in the drive or the drive is not ready.
ENXIO	Indicates that there was an attempt to write to a tape that is at EOM.
EPERM	Indicates that this subroutine requires appropriate authority.
ETIMEDOUT	Indicates a command has timed out.
EWRPROTECT	Indicates an open operation requesting read/write mode was attempted on a read-only tape.
EWRPROTECT	Indicates that an ioctl operation that affects the media was attempted on a read-only tape.

Reliability and Serviceability Information

Errors returned from tape devices are as follows:

Error	Description
ABORTED COMMAND	Indicates the device ended the command.
BLANK CHECK	Indicates that a read command encountered a blank tape.
DATA PROTECT	Indicates that a write was attempted on a write-protected tape.
GOOD COMPLETION	Indicates that the command completed successfully.
HARDWARE ERROR	Indicates that an unrecoverable hardware failure occurred during command execution or during a self-test.
ILLEGAL REQUEST	Indicates an illegal command or command parameter.
MEDIUM ERROR	Indicates that the command terminated with a unrecovered media error condition. This condition may be caused by a tape flaw or a dirty head.
NOT READY	Indicates that the logical unit is offline.
RECOVERED ERROR	Indicates that the command was successful after some recovery was applied.
UNIT ATTENTION	Indicates the device has been reset or powered on.

Medium, hardware, and aborted command errors from the above list are to be logged every time they occur. The ABORTED COMMAND error may be recoverable, but the error is logged if recovery fails. For the RECOVERED ERROR and recovered ABORTED COMMAND error types, thresholds are maintained; when they are exceeded, an error is logged. The thresholds are then cleared.

Note

There are device-related adapter errors that are logged every time they occur.

Error Record Values for Tape Device Media Errors

The fields defined in the error record template for tape-device media errors are:

Field	Description
`Comment`	Equal to tape media error.
`Class`	Equal to H, indicating a hardware error.
`Report`	Equal to TRUE, indicating this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating an error log entry should be created when this error occurs.
`Alert`	Equal to FALSE, indicating this error is not alertable.
`Err_Type`	Equal to PERM, indicating a permanent failure.
`Err_Desc`	Equal to 1332, indicating a tape operation failure.
`Prob_Causes`	Equal to 5003, indicating tape media.
`User_Causes`	Equal to 5100 and 7401, indicating a cause originating with the tape and defective media, respectively.
`User_Actions`	Equal to 1601 and 0000, indicating respectively that the removable media should be replaced and the operation retried, and that problem determination procedures should be performed.
`Inst_Causes`	None.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 5003, indicating tape media.
`Fail_Actions`	Equal to 1601 and 0000, indicating respectively that the removable media should be replaced and the operation retried and that problem determination procedures should be performed.

The Detail_Data field contains the command type, device and adapter status, and the request-sense information from the particular device in error. The Detail_Data field is contained in the err_rec structure. This structure is defined in the /usr/include/sys/errids.h file. The sc_error_log_df structure, which describes information contained in the Detail_Data field, is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Error-Record Values for Tape or Hardware Aborted Command Errors

The fields in the err_hdr structure, as defined in the /usr/include/sys/erec.h file for hardware errors and aborted command errors, are:

Field	Description
`Comment`	Equal to a tape hardware or aborted command error.
`Class`	Equal to H, indicating a hardware error.
`Report`	Equal to TRUE, indicating this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating an error log entry should be created when this error occurs.
`Alert`	FALSE, indicating this error is not alertable.
`Err_Type`	Equal to PERM, indicating a permanent failure.
`Err_Desc`	Equal to 1331, indicating a tape drive failure.
`Prob_Causes`	Equal to 6314, indicating a tape drive error.
`User_Causes`	None.
`User_Actions`	Equal to 0000, indicating that problem determination procedures should be performed.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 5003 and 6314, indicating the failure cause is the tape and the tape drive, respectively.
`Fail_Actions`	Equal to 0000 to perform problem determination procedures.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Error-Record Values for Tape-Recovered Error Threshold Exceeded

The fields defined in the err_hdr structure, as defined in the /usr/include/sys/erec.h file for recovered errors that have exceeded the threshold counter, are:

Field	Description
`Comment`	Indicates the tape-recovered error threshold has been exceeded.
`Class`	Equal to H, indicating a hardware error.
`Report`	Equal to TRUE, indicating this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating an error log entry should be created when this error occurs.
`Alert`	Equal to FALSE, indicating this error is not alertable.
`Err_Type`	Equal to PERM, indicating a permanent failure.
`Err_Desc`	Equal to 1331, indicating a tape drive failure.
`Prob_Causes`	Equal to 5003 and 6314, indicating the probable cause is the tape and tape drive, respectively.
`User_Causes`	Equal to 5100 and 7401, indicating that the media is defective and the read/write head is dirty, respectively.
`User_Actions`	Equal to 1601 and 0000, indicating that removable media should be replaced and the operation retried and that problem-determination procedures should be performed, respectively.
`Inst_Causes`	None.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 5003 and 6314, indicating the cause is the tape and tape drive, respectively.
`Fail_Actions`	Equal to 0000, to perform problem determination procedures.

The Detail_Data field contains the command type, device and adapter status, and the request-sense information from the particular device in error. This field is contained in the err_rec structure. The err_rec structure is defined in the /usr/include/sys/errids.h file. The Detail_Data field also specifies the error type of the threshold exceeded. The sc_error_log_df structure, which describes information contained in the Detail_Data field, is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Error Record Values for Tape SCSI Adapter-Detected Errors

The fields in the err_hdr structure, as defined in the /usr/include/sys/erec.h file for adapter-detected errors, are:

Field	Description
`Comment`	Equal to a tape SCSI adapter-detected error.
`Class`	Equal to H, indicating a hardware error.
`Report`	Equal to TRUE, indicating this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating an error log entry should be created when this error occurs.
`Alert`	Equal to FALSE, indicating this error is not alertable.
`Err_Type`	Equal to PERM, indicating a permanent failure.
`Err_Desc`	Equal to 1331, indicating a tape drive failure.
`Prob_Causes`	Equal to 3300 and 6314, indicating an adapter and tape drive failure, respectively.
`User_Causes`	None.
`User_Actions`	Equal to 0000, indicating that problem determination procedures should be performed.
`Inst_Causes`	None.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 3300 and 6314, indicating an adapter and tape drive failure, respectively.
`Fail_Actions`	Equal to 0000, to perform problem-determination procedures.

The Detail_Data field contains the command type and adapter status. This field is contained in the err_rec structure, which is defined by the /usr/include/sys/err_rec.h file. Request-sense information is not available with this type of error. The sc_error_log_df structure describes information contained in the Detail_Data field and is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Error-Record Values for Tape Drive Cleaning Errors

Some tape drives return errors when they need cleaning. Errors that occur when the drive needs cleaning are grouped under this class.

Field	Description
`Comment`	Indicates that the tape drive needs cleaning.
`Class`	Equal to H, indicating a hardware error.
`Report`	Equal to TRUE, indicating that this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating that an error-log entry should be created when this error occurs.
`Alert`	Equal to FALSE, indicating this error is not alertable.
`Err_Type`	Equal to TEMP, indicating a temporary failure.
`Err_Desc`	Equal to 1332, indicating a tape operation error.
`Prob_Causes`	Equal to 6314, indicating that the probable cause is the tape drive.
`User_Causes`	Equal to 7401, indicating a dirty read/write head.
`User_Actions`	Equal to 0000, indicating that problem determination procedures should be performed.
`Inst_Causes`	None.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 6314, indicating that the cause is the tape drive.
`Fail_Actions`	Equal to 0000, indicating to perform problem-determination procedures.

The Detail_Data field contains the command type and adapter status and also the request-sense information from the particular device in error. This field is contained in the err_rec structure, which is defined by the /usr/include/sys/errids.h file. The sc_error_log_df structure describes information contained in the Detail_Data field and is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Error-Record Values for Unknown Errors

Errors that occur for unknown reasons are grouped in this class. Data-protect errors fall into this class. These errors, detected by the tape device driver, are never seen at the tape drive.

The err_hdr structure for unknown errors describes the following fields:

Field	Description
`Comment`	Equal to tape unknown error.
`Class`	Equal to all error classes.
`Report`	Equal to TRUE, indicating this error should be included when an error report is generated.
`Log`	Equal to TRUE, indicating an error-log entry should be created when this error occurs.
`Alert`	Equal to FALSE, indicating this error is not alertable.
`Err_Type`	Equal to UNKN, indicating the error type is unknown.
`Err_Desc`	Equal to 0xFE00, indicating the error description is unknown.
`Prob_Causes`	None.
`User_Causes`	None.
`User_Actions`	None.
`Inst_Causes`	None.
`Inst_Actions`	None.
`Fail_Causes`	Equal to 0xFFFF, indicating the failure cause is unknown.
`Fail_Actions`	Equal to 0000, indicating that problem-determination procedures should be performed.

The Detail_Data field contains the command type and adapter status, and the request- sense information from the particular device in error. The Detail_Data field is contained in the err_rec structure. This field is contained in the /usr/include/sys/errids.h file. The sc_error_log_df structure describes information contained in the Detail_Data field and is defined in the /usr/include/sys/scsi.h file.

Refer to the Small Computer System Interface (SCSI) Specification for the applicable device for the format of the particular request-sense information.

Files

/dev/rmt0, /dev/rmt0.1, /dev/rmt0.2, ..., /dev/rmt0.7,

/dev/rmt1, /dev/rmt1.1, /dev/rmt1.2, ..., /dev/rmt1.7,...,

/dev/rmt255, /dev/rmt255.1, /dev/rmt255.2, ..., /dev/rmt255.7

Provide an interface to allow SCSI device drivers to access SCSI tape drives.

Related Information

The rhdisk special file, rmt special file.

The close subroutine, ioctl subroutine, open subroutine, openx subroutine, read subroutine, write subroutine.

A Typical Initiator-Mode SCSI Driver Transaction Sequence in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.

Required SCSI Adapter Device Driver ioctl Commands in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.

Understanding the Execution of Initiator I/O Requests in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.

SCSI Error Recovery in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.

Understanding the sc_buf Structure in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.

SCSI Adapter Device Driver.